3ERNSBACK SPECIALTY SERIES Q3 49604 …americanradiohistory.com/Archive-Hobbyist-Specials/...XK-500 Digital / Analog Trainer A complete mini -lab for building, testing, prototyping

Projects you can build! 3ERNSBACK SPECIALTY SERIES Q3 49604

1993 ELEC RONICSPopular HOBBYISTS

Electronics°han ook TM

29 GOOF -PROOFPROJECTS

For you to buildat home in the evenings

TALKING COMPASSIt tells you where you're going

TINY TUNERPassive front end for a receiver

BABY MONITORLet your ears do the watching

SOLDERING IRON CONTROLLERTone down the excess heat

VOICE DISGUISERLet a knob change your tone

MESSAGE RECORDERNo tape, just solid-state

8 -CHANNEL AUDIO SWITCHEFor your audio/visual syste

0 12 7

32

$3.95 U.S.$4.50 CANADA

z

Miniature Tracking

..-.Transmitter

Takes one evening to build!

NEGATIVE ION GENERATORMake the air you breathe safer

ELECTRONIC PIANO TUNERPull strings for better sound

HOT CANARIES

e. Tweets that don't need a cage

DARKROOM LIGHT METERGet a perfect print first try

ELEPHONE RING CONVERTERCreate a smooth warble

VOICE MAIL ALERTA blink keeps you informed

GEIGER RADIATION COUNTERCheck out the house and job

Vt.,*-11.111111111111

48 HOURSHIPPING

OR

ELENCO & HITACHI & B+ K PRODUCTS CALLO TOLDERL FREE1-800-292-7711

1-800-445-3201 (Can.)AT DISCOUNT PRICESELENCO OSCILLOSCOPES

S-1325 25MHz $349Dual Trace Oscilloscope

S-1340 40MHz $495Dual Trace Oscilloscope

S-1360 60MHzDual Trace, Delayed Sweep

Automatic beam finder Built-in component tester 1mV sensitivity Dual time base

$775

B+K OSCILLOSCOPES2120 - 20MHz Dual Trace $3952125 - 20MHz Delayed Sweep $5391541B - 40MHz Dual Trace $7492160 - 60MHz Dual Trace, Delayed Sweep,

Dual Time Base $9492190 - 100MHz Three Trace Dual Time Base,

Delayed Sweep $1,3952522 - 20MHz / 1 OMS/s Storage $8951442 - 20MHz Portable $1,2291443 - 40MHz Battery / AC operated with

Cursor & Readouts $1,439

1.0GHz PORTABLESPECTRUM ANALYZERModel 2610 $2,595.95

AC/DC operation (battery included) 70dB dynamic rangeIN Resolution bandwidth of 10kHzII 500 and 7552 input impedance (switch selec-table)II Fixed bandwidth setting for viewing TV signals Field calibratible with internally generated100MHz, 80dB signal

Hitachi Compact Series ScopesV-212 - 20MHz Dual Trace $409V-525 - 50MHz, Cursors $975V-523 - 50MHz, Delayed Sweep $949V-522 - 50MHz, DC Offset $849V-422 - 40MHz, DC Offset $749V-222 - 20MHz, DC Offset $625V-660 - 60MHz, Dual Trace $1,095V -665A - 60MHz,DT, w/cursor $1 325V-1060 - 100MHz, Dual Trace $1,375V -1065A - 100MHz, DT, w/cursor $1,649V-1085 - 100MHz, QT, w/cursor $1,995V -1100A - 100MHz, Quad Trace $2 195V-1150 - 150MHz, Quad Trace $2 695

Hitachi RSO SeriesRSO's feature; roll mode, averaging, savememory, smoothing, interpolation, pretrigger-ing, cursor measurements.

VC -6023 - 20MHz, 20MS/s $1 650VC -6024 - 50MHz, 2OMS/s $1,950VC -6025A - 50MHz, 2OMS/s $2,350VC -6045A - 100MHz, 4OMS/s CallVC -6145 - 100MHz, 100MS/s Call

Digital Capacitance MeterCM -1550B

$58.959 Ranges

.1p1-20,000ufd.5% basic accy.

Zero control w/ CaseBig 1' Display

Digital LCR MeterLC -1801

$125Measures:

Coils 1uH-200HCaps .1pf-200uf

Res .01-20M

Big r Display

Multimeter withDuo- Capacitance &

Transistor Tester

$55 CM -15008Reads Volts, Ohms

Current, Capacitors,''-":" Transistors and

Diodes / with case

FLUKE MULTIMETERSScopemeters (All Models Available Call)Model 93 $1,225.00Model 95 1,549.00Model 9710 SeriesModel 10Model 12

1,795.00

$62.95$79.95

70 SeriesModel 7011 $65.00Model 7711 $145.00Model 7911 $169.0080 SeriesModel 87 $289.00

Quad Power Supply XP -580

$69.952-20V @ 2A

12V @ to5V @ 3A

-5V @ .5A

Fully regulated and short circuit protected

Triple Power Supply XP -620Assembled $75

Kit $502 to 15V @ 1A,

-2 to -15V @ IA(or 4 to 30V @ 1A)

and 5V @ 3AAll the desired features for doing experiments.

Features short circuit protection, all supplies

AM/FM TransistorRadio Kit

with Training Course

Model AM/FM 108

$27.9514 Transistors 5 Diodes

Makes a great school project

True RMS 41/2Digit Multimeter

M -700T

$135.05% DC Accuracy.1% Resistancewith Freq. CounterData Hold

Sweep/Function Generatorwith Freq. Counter

$259Elenco

Model GF-8026Sine, Square, Triangle, Pulse, Ramp.2 to 2MHz, Freq Counter .1-10MHz

Internal Linear & Logic Sweep

Function Generator

Biox

#9600

$28.95

Provides sine, triangle, squareKit wave from 1Hz to 1MHz

$26.95 AM or FM capability

Learn to Build and ProgramComputers with this Kit

Includes: All Parts, Assembly and Lesson Manual

Model

MM -8000

$129.00

Smiling from scratch you build a complete system. OurMicro -Master trainer teaches you to write into RAMS,ROMs and run a 8085 microprocessor, which usessimilar machine language as IBM PC.

Elenco Wide BandSignal Generators

SG -9000 $129RF Freq 100K-450MHz AM Modula-

tion of 1KHz Variable RF output

SG -9500 w/ Digital Display &150 MHz built -In Counter $249

XK-500 Digital / Analog TrainerA complete mini -lab for building, testing, prototyping analog and digital circuitsElenco's Digital/Analog Trainer is specially designed for school projects, with 5 built-in powersupplies. Includes a function generator with continously variable, sine, triangular, square waveforms. All power supplies are regulated and protected against shorts.

Power Suppliese Variable Power SupplyIII +125 to 20VDC @ .5 Amp

(+1.25 to 15VDC @ I Amp)II -1.25 to -20VDC @ .5 Amp

(-1.25 to -15VDC @ 1 Amp) +12VDC @ 1 Amp -12VOC @ I AmpII +5VDC @ 1 Amp 30VAC Center tapped

@ 15VAC at 1 Amp

Analog - Section Function Generator Sine,

Triangular, Square wave forms Frequency adjustable in five

ranges from 1 to 100KHzII Fine frequency adjust Amplitude adjust DC offsetII Modulation FM -AM

Digital - SectionIII Eight data swiches Two no bounce logic switches 8 LED readouts TTL buffered Clock frequency 1 to 100KHz Clock amplitude 5VPP square wave

Breadboards $159.95 2 breadboards, each contain:

840 tie points (total 1,680) Assembled

WE WILL NOT BE UNDERSOLD C&S SALES INC.UPS SHIPPING 48 STATES 5'

1245 ROSEWOOD, DEERFIELD. IL 60015IL RES 7 5 TAX ,S3 min 510 max

FAX 708-520-0085 (708) 541-0710PROBES INCL ALL SCOPES & METERS

15 DAY MONEY BACK GUARANTEEFULL FACTORY WARRANTYWRITE FOR FREE CATALOG

CIRCLE 8 ON FREE INFORMATION CARD

ASAP JIT MRPOUR DISTRIBUTORS HELPABBREVIATE YOURPROCUREMENT CYCLE!

_fiery A4 Inc AerovacAluminum Llectrolytk Capauturs for DC

Applicsnons and AL Mom, Swung

AMPLietantal,11cctrunit Connectors,

IC sockets tWA Switches

CAROLElectronic and Cecina' Etre and Cable

and Power Sappls Cauds

A COMPANY OP

Dale Electronics, loc.St es. stassorks. Oscillators, Displays,

& Thermistors

DC Film and REI Suppression Capacitors.AC Oil Capacitors. EMI Filters

/MX CORPORATIONMLC, Tantalum and Thin Film

Capacitors, Resistors,Networks, Trimmers,

Oscillators. Resonators, Filtersand Piero Devices

Typing. rondos. Hose Sleevings, Splices,Insu:an,1 and Cable Dunes+ Products

,C.44.WyCcotattiINDUSTRIES. INC.

BATTERIES: Computer, CordlessPhone. Scanner & It/C.

ANTENNAS. Girdle, Phone (metal &rubber t. Scanner Bumpers,Grommets and Stik -On Feet

MAN SPEER ELECTRONICS, INC.Resistors. SNIT Tantalum Capauton Inductor.

Resistor Networks. SMT Thermistors

KEMETElectronics CorporationSolid Tantalum. Multt- LayerCeramic. and Surface Mount

Capacitors

Tantalum Capacitors, Wel & FoilCapacitors. Resistor Networks,

Resistor Capacitors Networks, Filters

MALLORY

wire. Cable. rsbing. Fiedronicintermiinect 'radix a

e BURNDYan FCI Company

(i»tnectvwa

BussmannFuses, Fuseholde.s. Fuse Blocks.

and Fuse Accessories

niCATIBCXEIZATnranua AMis [Mr

WialionsWire, Cable and Tubing

E'TNEaton Corporation, Commercial& Military Controls Operation

Switches. Relays. Displays id Keyboards

North American Capacitor CompanyTantalums, Aluminum. Sun:alerts

Ceramics, Films. AC's and RFI Filters

Philips ECGA North American Philips Company

semiconductors. Test Equipment.Re 12)1 AA Parts and

Chemicals

SwdollacraftA Moollhooss Company

Swathes Gnomon Jacks. Plugs.JackDelds a Audio ftexessories

C E CORNELLOUBILIER

Capacitors - AluminumElectrolytics, MICA. Al: o.: K.:nand

Da Pont Connector Systems

11P0

An expanding line of reliableInterconnections. Packaging, and

Subsystems

A

GERNSBACKPuBi iCA7 ON

Popular Electrodes Wovenlectonay sioy Magazine

- ManhattanElectrical and t lectron, St ire

Cable and Connectors

1111MEMI/RATA EFIE NORTH AMERICA

Monolithics, Discs, Variable Capacitors,Oscillators Potentiometers. III/EMI Filters.

Microwave. Su -face Mount Capacitors

t. GENERALo' DEVICES

Electronic tiara...sue

t,des, (bans, CAW Carriers. Shelves.lacks. Cabinets. Enclosures

NTE aFrTRONICS,WORUNNOt inane., FOR WARN RPM IMO Oa

Semiconductors, Resistors.Capacitors. Relays

m Roedersteintent and all Suppressi..n (Apac,, rsAluminum and Tantalum EletAn.tsut

Loudspeakers and Commensal Sound Carpzul,45 and Ite,siorsRodin:is

Thomson Consumer Electronics, Inc.

Cleaners Deur:sets S webs i Wipes.Brush, and Wick

Distnbutur and Special Productsleptacenierit pans for EA and GEconsumer electrootcs products

Whenever you need electronic products, makeyour initial call to a distributor. Distributorshelp speed up your time to market, providingthe convenience, the economy, the value, andabove all, the service that helps make youcompetitive.

The sponsors of this message know howimportant it is - to us and to your MRP - toget product ASAP or JIT. Another importantabbreviation is EIA. Our participation in theElectronic Industries Association's ComponentsGroup makes us all more competitive, through

fostering better working relations and coherentindustry standards, and through the sharing ofideas to help both buyers and sellers.

In choosing your component supplier, look forthe marks of leadership - availability throughdistr_bution and membership in the EIA.

Electronic IndustriesAssociation/Components Group2001 Pennsylvania Avenue, N.W. 11th FloorWashington, D.C. 20006Phone: (202) 457-4930 Fax: (202) 457-4985

Committed to the competitiveness of theAmerican electronics producer

Get your phone to warble your way(See page 55)

You won't recognize your own voice(See page 73)

Spare the heat and save the part!(See page 92)

The play transmitterthat can do a loto/ work.(See page 51)

2

Elect ronics®

1993Popular

Contents

Editorial 4

New Products 6

Electronics Library 10

Negative -ion Generator 13Make the air you breathe safer!

How to Electronically Tune Pianos 15Let electronics lend a helping hand.

Voltage Adapter for Your Car 21Your car can power your boombox or Discman.

Miniature Tracking Transmitter 23Track down your dog wherever he roams.

Universal RS -232 Connector 25Solves problems and saves hours of toil.

Voice Mail Alert 27Know at a blink there's Voice Mail for you!

The Incredible Hot Canaries 29Enjoy the songs without newspaper liner.

The Electromagnetic Ring Launcher 32A pipsqueak electro-propulsion launcher.

Personal Message Recorder 35No tape, just solid state.

Geiger Counter 38Check your house out-you never know!

An Enlarger Light -meter for Photographic Printing 42Get a perfect print on the first try.

Portable 2 -MHz Frequency Counter 45Go for it! You can't beat the price.

49-MHZ FM Transmitter 51Could be a toy or working tool.

Telephone Ring Converter 55Have your phone warble as you like it.

As a service to readers, Popular Electronics 1993 Electronics Hobbyists Handbook publishes available plans orinformation relating to newsworthy products. techniques and scientific and technological developments. Because ofpossible variances in the quality and condition of materials and workmanship used by readers, we disclaim ant.responsibility for the safe and proper functioning of reader -built protects based upon or from plans or information publishedin this magazine.

ELECTRONICSHOBBYISTShandbook

Baby Monitor 57Let your ears do the 'watching' when you're not there.

Automatic Porch -Light Control 63Let of Sol do the switching.

Wire Beams: Gain on the Cheap 66Get more bangs per buck out of your rig.

Holiday Light Tester 70Don't curse the dark, build this tester.

Voice Disguiser 73Let a knob change your voice.

One -Amp Current Injector 77How low can you get in ohms? Very low.

Talking Compass 80It's nice that a voice is with you when you're lost.

Automatic Power Switch for your TV 83Power up and down with your VCR remote control.

Electronic Fishing Lure 86Catch the big one with a little LED

Tiny Tuner 88A tunable, passive front end for your receiver

3X3 Visual Continuity Tester 90You find the connection and the resistance.

Soldering Iron Controller 92Tone down the heat when you don't need it.

Eight -Channel Audio Switcher 94And more inputs to your audio-visual system.

A "Quick & Dirty" Quad 98It goes up quickly and pulls 'em in!

Bass and Treble Booster Controls 100An add-on that's a plus!

Classified Advertising 111

Advertising Index and Sales Offices 112

Since some of the equipment and circuitry described in Popular Electronics 1993 Electronics Hobbyists Handbookmay relate to or be covered by U.S. patents, we disclaim any liability for the infringement of such patents by the making.using, or selling of any such equipment or circuitry, and suggests that anyone interested in such projects consult a patentattorneyPopular Electronics 1993 Electronics Hobbyists Handbook is published annually by Gernsback Publications Inc. All-ights reserved. Printed in U.S.A. Single copy price $3.95. Canadian G.S.T. Registration No. 125166280. Canada $4.50.c.Copyright Gernsback Publications Inc., 1993.

You don't needperfect pitch for perfect tuning(See page 15)

Check your local's radiation pulsesto keep your pulse going

(See page 38)

Tune in h,1.')\: zaul tune out anxiety(See page 57)

Counting pulses and Cvclesup to two 'nation is no problem

(See page 45r. 3

4

1993 ELECTRONICSropmhz HOBBYISTS

handbook ,r

Larry StecklerENE CET

Editor -In -Chief and Publisher

Juliam S. MartinHandbook Editor

Byron G. Weis, K2AVBAssociate Editor

POPULAR ELECTRONICSEDITORIAL DEPARTMENT

Carl LaronEditor

Robert A. YoungAssociate Editor

John J. YaconoAssociate Editor

Ted ScedutoAssociate Editor

Kathy TerenziEditorial Assistant

Marc SpiwakEditorial Associate

PRODUCTION DEPARTMENT

Ruby M. YeeProduction Director

Karen S. BrownProduction Manager

Marcella AmorosoProduction Assistant

Lisa RachowitzEditorial Production

ART DEPARTMENT

Andre DuzantArt Director

Inlae LeeIllustrator

Russell C. TrueIsonIllustrator

Jacqueline P. CheeseboroCirculation Director

Michele TorrilloP -E Bookstore

BUSINESS AND EDITORIAL OFFICES

Gernsback Publications, Inc.500-B Bi-County Blvd.

Farmingdale, NY 117351-516-293-3000

Fax: 1-516-293-3115President: Larry Steckler

Advertising Sales offices listed on page 112

Cover photography by Diversified Photo Services

Composition byMates Graphics

18 ABCMEMBER

Since some of the equipment and circuitry described in1993 ELECTRONICS HOBBYIST HANDBOOK may relateto or be covered by U.S. patents, 1993 ELECTRONICSHOBBYIST HANDBOOK disclaims any liability for the in-fringement of such patents by the making, using, or selling ofany such equipment or circuitry, and suggests that anyoneinterested in such projects consult a patent attorney.

Editorial

You're holding in your hands thelatest issue of the PopularElectronics' ElectronicsExperimenter Handbook. Theeditorial staff knows that you willenjoy it more than we did whenwe put it together. Our task was alabor of love. We selected thebest of the projects that appearedin Popular Electronics during1992 and put them in one tightlypacked handbook. We say theprojects are the best-based notonly on what we believe to betrue, but we also evaluated ourreader& responses to reinforceour decisions.

The projects are time rated andyou should know somethingabout the time rating system. Forexample, for some of us withamply -packed spare partssupplies and ready access tocommercial parts suppliers,obtaining project parts is noproblem at all. Not so for manyhobbyists and the novice. In fact,the most grueling part of projectbuilding could very well be thewait for mail -ordered parts toarrive. Thus, you would expect usnot to consider the acquisition -of -parts time as a factor of theproject's construction time,because of the variables involved.

We consider the project'sconstruction time to begin after allthe parts are available, and thatincludes the printed -circuit board.Although there are modernmethods for adding resist

patterns to the copper -cladsurface of a board, even that timeis an indeterminate quantity. So,the gun fires to start the clockwhen all the parts are on theworkbench and you plug in thesoldering iron.

Projects that require tuning,alignment or adjustment have thetime interval thus required addedto the total time. The making ofsimple boxes, cabinets, etc., andother minimal cosmetic taskssuch as nameplates, dialmarkings, paint jobs, etc., areincluded in the total time. Asbefore with the parts, materialsand equipment necessary for thetask to be completed, they mustbe on the workbench or availablenearby so as not to interrupt theflow of work.

We assume that most of the workwill be done in the evenings afteryour normal work day, so that atypical one -evening project takesabout three hours. Expect a giveor take of one hour dependingupon your skill and the qualityand availability of tools andequipment on your workbench.For example, we consider that atleast one solder connection mustbe redone for whatever reason. Ifyou have a "suction -tip" de -soldering iron, add 30 seconds tothe task. If you use a copperbraid to sap off the solder, addtwo minutes. If you let the tip ofthe iron do the job, add fiveminutes. (Of course, the latter

technique should not be used!)

A small drill press, power jig saw,desk -top illuminated magnifyinglens, electric screw -nut driver, andother convenient hand toolsspeed up most hobbyist'sprojects. Also, what many readersfail to do is study the text carefullybefore they begin to build aproject. Know what you have todo, then do it. Don't look for shortcuts or redesigning efforts as youassemble the project. It's best tostop all work and seriously thinkout and plot out what you want todo and how to do it. In mostcases, it is wiser to complete theproject, get it working, thenredesign for a specific purpose.

Now you know the time -evaluation system, look for the"Project Time" lable for eacharticle. (See above.) The editorswould like to know if this systemwas of value to you, so drop us aline and tell us what you think andwhat you experienced.Remember, your views are oureyes. Happy project building.

AfaJulian S. MartinHandbook Editor

peototessMotion!

Build BORIS the miniature motoriess walling

machine with Muscle Wires.elhey contract up to

five percent when powered. Remove power and

they relax, ready for maroons more cycles.Create &erect Timor action without heavy gem,

coils, or motors. Use Muscle Wires in robots,models, planes, radroods - anywhere you need

smalL strong all -electric motion.

What Are Muscle Wires?Muscle Wires are highly processed strands of a

nickel-titanium alloy called nitinol. At roomtemperature they are easily stretched by up to 5%of their length. When conducting an electriccurrent they return to their original -un.stretchecrshape with a force thousands of times their weight.

How strong are Muscle Wires?The force a wire pulls with varies with size, from

35 to 330 grams. For more strength, use severalwires in parallel.

How fast can Muscle Wires activate?They cost' a as fast as they are heated - as

quickly as 1/1000 of a second. To relax, the wiremust cool again. Rates of many cycles per secondare possible with active cooling.

Q&A

Flexinol Muscle Wire S ecIfications

Wire Diameter 50 prIl 100 pm 150 µmResistance 510 S2/m 150 Dim 50 Wm

Contract Force 35 grams 150 grams 330 gramsTypical Current 50 mA 180 mA 400 mA

How much power do Muscle Wires need?Power vanes with wire diameter, length, and

surrounding conditions. Once the wire has fullyshortened, power should be reduced to preventoverheating.

What are the advantages of Muscle Wires?Small size, light weight, low power, very high

strength -to -weight ratio, precise control, AC or DCactivation, long life and direct linear action andmuch more!

Get our new 112 page Book and DeluxeSample Kit with plans for BORIS and 14other motorless motion projects. Includesone meter each of 50, 100 and 150 pindiameter Muscle Wire - everything youneed to get moving today!

Ask for our FREE Muscle Wires Technical Brodivre

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New ProductsFANNYPAK TOOL CASE

For hands -free carrying of those few selecttools that you just can't do without, theToolpak Fannypak from Paktek can be wornaround your wasit. The compact tool casefeatures a fold -out tool panel and threeinternal compartments, all designed to holda variety of tools in a way that is both

convenient and well -organized. The Fanny-pak is made of 1000-dernier Cordura, amaterial that is strong enough to withstandthe day-to-day rigors of field -service work,yet soft enough to protect tools and to wearcomfortably around the waist.

The Toolpak Fanypak costs $24.95. Formore information, contact Paktek Inc., 730782nd St. Ct. SW, Tacoma, WA 98498; Tel:800-258-8458.


"TOOL KIT" COMPACTMULTIMETERS

Four compact, budget -priced digital multi -meters from B K Precision offer 0.5% DCaccuracy. The Tool Kit DMM's offer usefulfunctions for technicians, installers, andhomeowners. All measure current to 10amps, voltage, and resistance; check di-odes; and have a continuity checker, large31/2 -digit LCD readouts, and transient andoverload protection. The basic unit is the

OLIO

M/[' TOOL OR 2103A

Model 2703A. Model 2704A adds AC cur-rent, capacitance, and transistor tests. TheModel 2706 adds a temperature -measure-ment function. Similar to the 2704A, the

Model 2707 has a built-in frequency counterand logic -probe functions.

Models 2703A, 2704A, 2706, and 2707DMM's have list prices of $39, $59, $79,and $89, respectively. For additional infor-mation, contact B + K Precision, Division ofMaxtec International Corporation, 6470West Cortland Street, Chicago, IL 60635;Tel: 312-889-1448; Fax: 312-804-9425.


SOLDERING -IRON CONTROLLER

A compact accessory from M.M. NewmanCorporation makes fixed -temperature sol-dering irons adjustable. When it is desirableto lower their full operating temperature, theDial -Temp soldering -iron controller lets theuser adjust the tip temperature based uponthe job at hand. The Dial -Temp is equippedwith a three -prong grounded plug and re-ceptacle. It gets plugged into any 117 -VACoutlet and the soldering iron is then pluggedinto the controller. Once connected, a knobon top of the unit is used to adjust thetemperature from 150°F to full heat. Com-patible with soldering irons from 15 to 1600watts and other devices that use heatingelements, the Dial -Temp has a 15 -amp

capacity. Besides controlling soldering -irontemperature, it can be used to moderate hotplates and to adjust wood -burning tools.

The Dial -Temp soldering -iron controllerhas a list price of $31.95. For additionalinformation, contact M.M. Newman Corpo-ration, 24 Tioga Way, P.O. Box 615,Marblehead, MA 01945; Tel: 617-631-7100;Fax: 617-631-8887.


TRI-FIELD METER

The Tri-Field Meter from AlphaLab indepen-dently reads AC electric fields, AC magneticfields, and radio/microwaves with multi -di-rectional sensors that read field strengths inall directions simultaneously. The meterreads all three types of fields both numer-ically and with a safe/borderline/high scalethat is weighted proportionally to the field'seffect on the human body. Thresholds arebased on epidemiological and laboratory

studies; although no absolute hazard levelshave been established, reduction of relativeexposure levels is recommended. The com-pact meter comes ready -to -use with battery,instructions, and a one-year limited warran-ty.

The Tri-Field Meter costs $144 postpaid($154 for Canadian orders). For furtherinformation, contact Alphalab, 1272 EastAlameda Avenue, Salt Lake City, UT84102-1703; Tel: 503-621-9701.


MINIATURE SOLDERING IRON

Designed for thermal efficiency, the AntexModel G/3U miniature soldering iron fromM.M. Newman Corporation features a heat-ing element placed directly under the tip.Because of that design, the 18 -watt unitperforms like a 30 -watt soldering iron. It isready to solder quickly by reaching 725°F inonly 45 seconds, the handle always stayscool, and the tip recovers instantly aftersoldering. The unit is positively groundedfrom the tip to protect sensitive electroniccomponents. It is available with more than

40 different styles of slide -on tips, rangingfrom a 0.012 -inch tapered needle point to a3/16 -inch diameter chisel. The tips are totallyinterchangeable and will not stick or bind.

The Antex Model G/3U miniature solder-ing iron, including a standard tip, costs$24.95. Replacement tips are priced from$1.55 each. For further information, contactM.M. Newman Corporation, 24 Tioga Way,P.O. Box 615, Marblehead, MA 01945; Tel:617-631-7100; Fax: 617-631-8887.


New ProductsWIRELESS MICROPHONE

Aimed at professional and serious amateurvideographers, Azden WHX-PRO micro-phone system has both the transmitter andthe antenna built into the microphone, mak-ing it completely wire -free. Its powerfulminiature receiver measures 3 x 21/2 inchesand can be attached to the camera with thesupplied shoe mount or with Velcro. Thetelescoping antenna features a shorter de-sign, allowing it to be placed in a shirtpocket. The WHX-PRO has two switchable

frequencies -169.445 and 170.245 MHz-and a range of more that 250 feet. Its three -position ON/STANDBY/OFF Switch reducesnoise when the microphone is passed fromperson to person during recording. Anoctagonal ring surrounding the windscreenprevents the microphone from rolling whenit is set down.

The WHX-PRO wireless microphone sys-tem has a suggested retail price of $275.For further information, contact Azden Cor-poration, 147 New Hyde Park Road,Franklin Square, NY 11010; Tel:516-328-7500; Fax: 516-328-7506.


FREQUENCYDETECTOR/COUNTER

Intended for use in counter -surveillance,police tactical situations, private investiga-tions, and secure installations,Optoelectronics Handi-Counter model 2300can also be used inexpensively in two-wayradio, ham radio, frequency monitoring ap-

plications. The counter features full eight -place readout resolution up to 2.4 GHZ; 10 -mV sensitivity for signal detection at max-imum distance from the transmitter, all theway through 900 MHz for cellular phoneuse; and a convenient display -hold switchso that the user won't have to remember orwrite down the detected frequency. Anoptional 600-mAH Ni-Cd battery pack isavailable.

The Handi-Counter model 2300 costs$99; the battery pack costs $29. For addi-tional information, contact Optoelectronics,Inc., 5821 NE 14th Avenue, Fort Lauderdale,FL 33334; Tel: 800-327-5912 or305-771-2050; Fax: 305-771-2052.


ONE -KNOB METAL DETECTOR

Hunting for treasure couldn't be easier thanwith Fisher Research Laboratory's model1212-X metal detector. Providing high perfor-mance with no extras, the unit has only one

knob (to set the trash -rejection level); notuning or meters are required. The 1212-Xoffers a deep search range, a cushioned"S" -shaped handle, a headphone jack, abuilt-in speaker, automatic VLF -ground re-jection, and automatic tuning. The metaldetector operates on just one 9 -volt battery,and has an eight -inch coil that is ESI(electro-static insulated) shielded to reducefalse signals.

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New Boolismonitors have entered a newera in radio -monitoring efficien-cy by interfacing their radioswith their computers. That ar-rangement allows them to tune,search, scan, log, analyze, de-code, and even do remotemonitoring, right from the com-puter keyboard. This book,which assumes that the readerhas some knowledge of com-puters, details the ins and outsof computerized radio monitor-ing, from scanning frequency

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one way or the other it has an effect onbiological systems.

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Build aNegative -IonGenerator

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To summarize a few points from hisbook, negative ions help elevatemood, enhance physical performanceand training, and sterilize harmful air-borne bacteria. An abundance ofpositive ions on the other hand can beheld responsible for a number of lowgradetigue, headaches, and anxiety.

There are detractors to this point ofview. So before I started to design anegative -ion generator, I did some re-search to find out if it would be worth-while. I surveyed approximately 100world-wide scientific reports on theeffects of negative ions from 1973through the present. I can report thatout of my survey approximately 80% ofthe citing's note the beneficial effects of

negative ions. Greater than 19% of thereports described no effect, and a few(less than 1%) detailed some detrimen-tal effect. Since the preponderance ofthe evidence supports the beneficialeffects of negative ions, I felt that build-ing an ion generator was a worthwhileproject. A summary of some of the ben-eficial effects reported by some re-searchers are listed in the boxed textentitled "The Positive Effects of NegativeIons." It is by no means an exhaustive list,it's just a sampling of the scientific bene-fits noted. But if this is the case it wouldbe to our benefit to improve the qualityof air that we breathe with a negativeion generator.

Despite the numerous scientific re-ports supporting the health benefits of

The Positive Effects of NegativeIons

Learning enhancement in normal andlearning -disabled children. The task usedto test the children was a dichotic listeningtest. Negative Ions can be used to decreaseamounts of radon in a building atmo-sphere.

In one animal study 1279 calves werebroken into two groups, one of 649 headand the other of 630 head, negative airionization was used to test for a prophylac-tic effectiveness against respiratory dis-eases. The results were remarkable: In thetreated group (649 head) 45 calves be-came sick and 3 died. In the control group(630 head) 621 became sick and 33 died. A 40-50% reduction of microbial air pol-lution in dental clinics. A test using college students showedimproved performance on a visual vig-ilance task.

In 1983 it was reported that chickensraised in a negatively ionized atmosphereshowed improved anabolic processes. Thechickens raised in negatively ionized airhad an overall greater weight than a controlgroup fed the same quality and quantity offeed. The meat of the treated group hadhigher protein and essential amino -acidcontent. In addition, higher concentrationsof vitamins E and A were found in theirlivers.

Bibliography

Negative Air Ion Effects on Learning Dis-abled and Normal Achieving Children, L.L.Morton and J.R. Kershner, University ofWindsor, Faculty of Education, Ontario,Canada, 1990

Effect of Negative Ion Generators in a SickBuilding, M.J. Finnegan, C.A. Pickering,F.S. Gill, I. Aston, and D. Froese, Depart-ment of Thoracic Medicine, WythenshaweHospital, Manchester, England, 1987

Aeroionization in Prophylaxis & Treatmentof Respiratory Disease in Calves., T.I. Sol-ogub, N.F. Borzenko, V.P. Zemlyanskiy. andK.F. Plakhotnyy, Russia 1984

Effect of Ionization on Microbial Air Pollu-tion in the Dental Clinic, J. Gabby, 0.Bergerson, N. Levi, S. Brenner, and I. Eli,Research Institute for Environment Health,Sackler School of Medicine, Tel Aviv, Isreal,1990

Effects of Ionized Air on the Performance ofa Vigilance Task, G.C. Brown and R.E. Kirk,Systems research Laboratories, Inc.,Brooks AFB, TX, 1987

-Negative Ions," J.E. Wright, Muscle & Fit-ness Magazine, January 1991

Effect of Artificial Air Ionization on Broilers,P. Stoianov, G. Petkov, and B.D. Baikov, VetMed Nauki. Bulgaria, 1983

PL1

Ti12V

R21K

Al15K

C1

1000

U1

555

DISCHARGEPOINT

DI 0IMD5210

L m

laT2

12V: 8KV

01TP120

C2T .047

R32.2K

R447053

C3

.002

C4.002

022N3055

Fig. I. This is the simple schemat'c for the Negative -Jon Generator. Note that it isbasically a timer that induces a high voltage in the windings of 77.

ionized air, no manufacturer of nega-tive -ion generators can make anyhealth -benefit claims without runningafoul of the FDA. For that reason I alsowill make no such claims. Instead, the

PARTS LIST FOR THENEGATIVE -ION GENERATOR

SEMICONDUCTORSU1-555 timer, integrated circuitQl-TIPI20 NPN Darlington transistorQ2 -2N3055 power transistorD1 -10,000 -volt, 10-mA silicon rectifier

diode (see text)BRI-4-amp, 50 -Ply bridge rectifier

RESISTORS(All resistors are Vi -watt 5% units.)R1 -15.000 -ohm R3-2200-ohniR2-I000-ohm R4-470 ohm

CAPACITORSCI -1000-µF, I5-WVDC electrolyticC2 -0.047-µF, polyester -filmC3, C4-.002 -µF, 6.000-WVDC,

ceramic -disc

ADDITIONAL PARTS AND MATERIALS11 -12 -volt, I.2 -amp power transfornierT2-12 volt to 8 kilovolt autotransformerFANI-12-volt DC fanEnclosure, line cord, switch. TO -3

socket and heat sink, perfboard, wire,solder, etc.

The following are available from ImagesCompany (P.O. Box 140742 StatenIsland, NY 10314-0024; Tel.718/698-8305): Dl ($1.50). C3 and C4($1.50 ea.), and 12 ($17.95). Includean additional $2.50 for shipping andhandling. NY residents must addappropiate sales tax.

NOTE: The above prices are subject tochange.

research papers supporting this articleare listed in the text entitled "Bibliogra-phy' so you can do the research onyour own and make your own decision.

The Ion Generator. The design of theNegative -Ion Generator is fairlystraighfforward (see Fig. 1). The circuit isa high voltage generator, It contains astandard 555 timer that's used to gener-ate square -wave pulses. The pulses areapplied to the base of the 11P120 NPNDarlington transistor. The Darlingtonprovides sufficient current to the baseof the 2N3055 power transistor to turn Iton. Each time that happens, currentflows through the high voltage auto -

transformer, T2. The high voltage lead ofthe transformer is connected to a 10kilovolt high voltage diode. Notice thepolarity of the diode. It is biased toplace a negative charge on C3 andC4, leaving the discharge point nega-tively charged. The voltage at the dis-charge point negatively charges theair forced past it by the fan.

The authors prototype was built onsections of perfboard using point-to-point wiring. ft is a suitable method thatyou can use in your own ion generatorprovided you follow some precautions:Make sure you place C3, 04, D1, andthe discharge point (which we'll de-scribe momentarily) on a piece of per-fboard all their own. The junctionsbetween those components should beat least a centimeter apart. Both thislittle high voltage board and the auto -

transformer should also be kept at leas'1 centimeter away from the perfboardcontaining the other components, thefan, and the power transformer.

(Continued on page 108)

Traditionally, piano -tuning has been theexclusive domain of

craftsmen who've spentyears perfecting their skills.Having to discern pitchesby ear, they were as muchpractitioners of art as of sci-ence, with accompanyingfees for their services rang-ing as high as $60. But thePrecision Audio -FrequencyGenerator described in thisarticle will change all ofthat.

Coupled with an os-cilloscope and a digital fre-quency counter, the gen-erator allows you to tune apiano or another instru-ment (say a violin) to an ac-curacy of 0.01 Hz, or better,throughout most of itsrange.

Just the Basics. A blockdiagram of the PrecisionAudio Frequency Gener-ator, which consists of sev-eral sub -circuits an au-dio-amplifier/filter circuit,an automatic level control,a variable voltage -con-trolled oscillator, a frequen-cy divider circuit, an inte-grator, and an audio output amp-isshown in Fig. 1.

An electret microphone element isused to pick up the audio tone pro-duced by the instrument. That signal isthen fed to an amplifier/fitter/level-con-trolled circuit and output via channel 1(cm) to an oscilloscope for display.

The variable voltage -controlled -os-cillator (VCO) is used to produce a sig-nal of from less than 10 kHz to more than99 kHz. The VCO output is fed to a digitalfrequency counter for display, and isalso routed to a chain of frequency di-viders, where the signal is divided by io.ioo, or Too, depending on the setting ofa selector switch.

From there, the selected signal fre-

How ToElectronicallyTune Pianos

And OtherInstruments

BY STEVEN A. BROWN

This circuit will let you use your oscilloscopeand digital frequency counter to tune pianos

and more to an accuracy of .01 Hz.

quency divides along two paths; onegoing to CH2 (which feeds the os-cilloscope's sweep synchronization in-put) and to an integrator that convertsthe squarewave output of the dividerinto a triangular waveform. The outputof the integrator is then amplified andfed to a set of stereo headphones viaan audio output jack.

A Closer Look. A complete sche-matic diagram of the Precision AudioFrequency Generator is shown in Fig. 2.An electret microphone element(which has a flat frequency response towithin 3 dB down to 20 Hz) is used to pickup audio from the piano or other instru-ment. The microphone element, con-

nected to J2, converts theaudio to an electrical stg-nal, which is fed to the non -inverting input of U2 -a (halfof an LM358 dual op -amphat is configured as a uni-ty -gain voltage follower).

At the same time, about4 volts DC is also deliv-

ered to U2-a's non -invert-ing input at input pin 3 via01 and R3, so that the mi-crophone signal rides onthe DC voltage. The outputor U2 -a is then fed to U2 -b,wnich is configured as aninverting amplifier. That op -amp provides a gain 40 dBwhen S1 is in the FLATposition. Capacitor C6 is in-cILded in the circuit to rolloft frequencies above4400 Hz. Those frequenciesare not wanted in this ap-plication.

When S1 is placed in theLP position, C7 rolls off fre-quencies above 13.5 Hz,which is an octave belowthe lowest note on the key-board, so that the rolloff is6 -dB -per -octave from thatnote upward. Placing S1 inLP position permits tuning ofthe ,owest two octaves of

the piano, where overtones would oth-erwise make the fundamental of thewaveform difficult to see.

The output of U2 -b at pin 7 is fed to acompander (U3). The compander,which is used as an automatic levelcontrol, provides a variable gain offrom 0 to 20 dB, depending on the inputlevel. Thus, U3 maintains a more con-stant output amplitude over a 10:1range for a rapidly -decaying note. Theoutput of U3 is fed via J3 (cH 1) to anoscilloscope.

The VCO portion of a CMOS phase -locked loop (U5) is used as the oscillatorin the circuit. The frequency of the VCOis adjustable via R10 (FINE) and R11(caapsE). For stability, a separate voltage 15

regulator, U4, is used to power U5 and itsassociated circuitry. Devices with a low -temperature coefficient were selectedfor the frequency -determining compo-nents, C15, R12, and R13, in the VCO.

The VCO's output is attenuated by a10:1 voltage divider, comprised of R15and R16 before being routed to J4,which is the output to an external fre-quency counter. The VCO output is alsofed through R14, which is used as a cur-rent limiter, to a chain of cascaded4017 CMOS decade counter/dividers(U6 -U8). Each counter/divider output isrouted via its associated resistor(R17 -R19, respectively) to rotary switchS2.

The squarewave output selected byS2 travels along two paths; in one path,the signal is routed to J5 (cH 2); in theother path, the signal is fed to an audiooutput circuit consisting of U9, Q2, andQ3. The portion of that signal that goesto the audio circuit is applied acrossC16 to the input of U9 -a (half of a sec-ond LM358 dual op -amp) through R20.Capacitor C16 is used to extend the risetime of the selected squarewave-out-put signal to 20 microseconds so that itdoesn't cause glitches to appear at CH 1,

The output of U9 -a can be adjustedvia R21, (in affect serving as a VOLUMEcontrol). The squarewave output of U9 -a is fed to U9 -b, which is configured as

MIC

FLAT

LP 0

AUDIOAMP. AND

FILTER oAUTOMATIC

LEVEL CH1

CONTROL

40dB

0-20 dB

VOLTAGE -

FREQUENCY CONTROLLED o CNTROSCILLATOR

DIGITALDIVIDERS

1000

1000

100

AUDIOAMPLIFIER

Fig. 1. The Precision Audio Frequency Generator is comprised of several sub -circuits-an audio amplifier/filter circuit, an automatic level control, a voltage -controlledoscillator, a frequency -divider circuit, an integrator, and an audio -output amp.

CH2

0 AUDIO

an integrator. The integrator transformsits squarewave input to a triangularwaveform, which approximates thewaveform of a vibrating string. The out-put of U9 -b is simultaneously fed to thebases of two transistors, Q2 and Q3, for

amplification. The output of that pair oftransistors is fed through C19 to J6. Con-necting a set of stereo headphones toJ6 allows that signal to be audibly com-pared to the pitch' of the note beingplayed.

PARTS LIST FOR THE PRECISION AUDIO- FREQUENCY GENERATOR

SEMICONDUCTORSUl, U4 -78L09, 9 -volt, 100-mA

voltage -regulator, integrated circuitU2, U9-LM358 dual op -amp,

integrated circuitU3-NE570 compander, integrated

circuitU5-CD4046 CMOS phase -locked loop,

integrated circuitU6, U7, U8-CD4017 CMOS decade

counter/divider. integrated circuitQI. Q2 -2N4401 (or similar) general-

purpose NPN silicon transistorQ3 --2N4403 (or similar) general-

purpose PNP silicon transistor

RESISTORS

(All fixed resistors are 1/4 -watt, 5% units,unless otherwise noted.)

R I -27,000 -ohmR2, R22 -47,000 -ohmR3, RI6, R20 -1000 -ohmR4, R5 -12,000 -ohmR6-I.2-megohmR7 -200,000 -ohm

R8, R9, R23, R24 -33,000 -ohmR10 -1000 -ohm linear -taper

potentiometerR11 -100,000 -ohm linear -taper

potentiometerR12 -12,000 -ohm, 1% metal -filmR13 -300,000 -ohm, I% metal -filmR14 -10,000 -ohmR15, R17 -R19 -9100 -ohmR21 -10,000 -ohm linear- or audio -taper

potentiometerR25470,000 -ohm

CAPACITORSCl, C4, C20 -47-µF, 16-WVDC,

electrolyticC2, C3, C13, C14 -0.22-µF, monolithic

ceramicC5-4.7-taF, 16-WVDC, electrolyticC6-27-pF, ceramic -discC7 -.01-µF, 10% polyesterC8 -C12, C17 -10-µF, 16-WVDC.

electrolyticC15 -0.001-µF, 5% polystyreneC16 -.01-µF. ceramic -disc

C18 -0.1-11F, 10% polyesterCI9-470 ILE 16-WVDC, electrolytic

ADDITIONAL PARTS AND MATERIALS11 -See textJ2 -1/H -inch mono phone jackJ3, J4, J5 -RCA or BNC jacks (see text)J6 -V8 -inch stereo headphone jackS1-SPST miniature toggle switchS2-SP3T rotary switch (see text)Perfboard materials, enclosure, electret

microphone element (Radio Shack270-090 or equivalent), knobs. 1/4 -inch heat -shrink, 12 -volt AC -to -DCadapter, Walkman -type stereoheadphones, shielded audio cablewire, solder, hardware, etc.

Note: The software described in the textfor the IBM or compatible PC isavailable for $10 postpaid fromAndromeda Electronics, 125 N.Prospect St., Washington. NJ 07882.NJ residents must add sales tax.Specify 5V4 -inch or 31/2 -inch disk.Check, money order, VISA, or M/Caccepted.

J1

+12V

+ 9V

9

Ul

J2

MIC

78L09

G

C2

47

C3.22

R1

27K

R247K

+ C4

T 47

01

2N4401

5V

R3

1K

2

4V 3

78L09

G

C13.22 M

C14.22

R101K

FINE

FRED. ADJ.

R11

100KCOARSE

C15.001

11

R1212K

R13300K

12

3 114 16

U54046

C7.01

FLAT

9 LPR6 S1

1.2MEG + 9V

R161K

R159.1K

1

NANR1410K

+ 9V

16

U64017

R201K

:4#*

C16.01

3

+ 9V

U9 a

R2110K

VOLUMER25

470K

C180.1

+4 5V

1/2 LM3584.5V

74- C1710

R2247K

5

R2333K

+9V a VA

U9 -b

4R2433K

1/2 LM358

C2047

)1+

124114

8 113 115

-0- +9V16

U74017

8

R179.1K

13

12 14

15

-o- +9V16

U84017

18 113

R18#9.1K

12

15

10010 0 1000--0 o ---

+4.5V 0 S2+4.0V

022N4401

*--e- + 9V

Fig. 2. One section of the Precision Audio Frequency Generator uses an electretmicrophone element to pick up audio from the piano. That signal is then processed andsent to one channel of a dual -trace oscilloscope. The other section of the circuit is usedto produce a variable frequency signal that is fed to a digital frequency counter andafter conditioning, is presented to the second channel of the scope and output to a set ofstereo headphones.

Construction. The author's prototypeof the Precision Audio Frequency Gen-erator was hard -wired on a section ofperfboard. Once you've collected all ofthe necessary components, begin as-sembling the circuit using Fig. 2 as aguide. It is suggested that you socketthe IC's. The benefit of using sockets isthat they help to avoid thermal andstatic -discharge damage to the IC's(especially the CMOS units, U5 -U8) dur-ing assembly.

Also, when assembling the board, at-tention should be paid to the partslayout. For example, to prevent feed-back from the output to the input, U2

and U3 should be positioned on theopposite side of the board from U9. Thecomponents that set the lower and up-per limits of the VCO frequency must betemperature -stable; capacitor C15should be a polystyrene unit, and bothR12 and R13 should be 1% metal -filmresistors.

Assemble the board -mountedportion of the project first, leaving theoff -board components (all of the jacksand controls) for last. Once that's done,label and solder over -sized lengths ofwire (which will be trimmed later) to theappropriate points on the board forconnection to the off -board compo-

032N4403

C19470

J4CNTR

R199.1K

J5CH2

J6AUDIO

nents. Note that Fig. 2 shielded audiocable is indicated for the connectionfrom J1 (the mic jack) to the circuit -board. Once you've completed the cir-cuit board assembly, check your workfor the usual construction errors: mis-connected components, improper po-larity, cold solder joints, etc.

Once you are reasonably sure thatthe circuit board has been properlywired, put the board to the side for awhile and begin preparing the en-closure that will house the board. Theauthor used a plastic enclosure with ametal lid to house the prototype. Pre-pare the enclosure by drilling several 17

PIANO SUPPLY HOUSES

American Piano Supply Co.Box 1005Clifton, NJ 07014

Ford Piano Supply166 East 82nd St.New York, NY 10028

Schaff Piano Supply Co.2009 N. Clybourn Ave.Chicago. IL 60614

Tuners Supply Co.94 Wheatland St.Somerville, MA 02145

1274 FolsomSan Fransisco, CA 94103

761 Piedmont Ave,Atlanta, GA 30308

holes in its lid-starting with four holesfor potentiometers R10, R11, and R21,and switch S2 across what will be theupper edge of the lid. Although S2 isshown as a single -pole, 3 -position rota-ry switch in Fig. 2, any single- or double -pole, multi -position switch will do.

Drill six more holes below the onespreviously drilled to accommodate allof the I/O jacks and controls, except J1.That jack should be mounted to theside of the enclosure. Note: Varioustypes of jacks were used for J1- J6. Forexample, J1 was selected to mate withan AC -to -DC adapter; for J2, the authorused a Ya-inch mono phone jack for J3and J5, he used RCA jacks (althoughBNC types are fine); for J4, a BNC jack(which might be replaced by an RCAunit); and for J6, a 1/8 -inch stereo head-phone jack. It will be necessary to drillappropriate size holes for each jacktype.

Once mounted, all of the jacks, ex-cept for J1, will be grounded via theenclosure lid. That means that it will notbe necessary to provide a ground wirefor each jack. However, the shield of themicrophone cable connected to J2should not be expected to serve as thesole ground -return for the outputs, es-pecially where the high -current audiooutput is concerned. To handle the ex-pected current, a separate wire shouldbe soldered between Q3's collectorand the ground terminal of J6. Theground terminal of J6 (which shouldcontact the lid of the enclosure), in turn,provides the necessary ground -returnpath. The remaining two terminals of J6should then be bridged and wired toC19.

Once the holes for the panel -

The author's prototype' circuit Kas hard -wired on a section of perfboard. Shown here isthe perfboard assembly wired to the' panel -mounted components prior to beinginstalled in its enclosure.

mounted components have beendrilled, drill a single hole in the side ofthe enclosure for J1. That jack requires aseparate connection to circuit ground.Mount the off -board components tothe enclosure and measure off the min-imum length of wire for each connec-tion that will be necessary to connectthe off -board components to theboard, and solder them in place. Keep-ing the wiring between the board andpanel -mounted controls and Jacksshort and direct helps to preventcrosstalk between channels. Once allof the off -board components havebeen wired to the board and the con-nections checked for accuracy, theboard should be rechecked for errorsbefore going on.

The final step before installing the cir-cuit into its enclosure is to insert the IC'sinto their sockets. Be very careful whenhandling the CMOS IC's; they're staticsensitive. Once the IC's have been in-stalled and properly seated, turn your

attention to the preparation of the mi-crophone element. Solder the micro-phone element to one end of a ten -

foot length of shielded audio cable orflexible coax. To the other end of thecable, solder a 1/8 -inch mono phoneplug. To provide strain relief, the micro-phone element should be slipped intoa 3/4 -inch length of 3/8 -inch diameterheat -shrink tubing. Afterward, fill thespace between the cable and the tub-ing with quick -setting two-part epoxy. Itisn't necessary to heat the tubing, anddoing so could damage the micro-phone element.

Before being placed into operation,the Precision Audio -Frequency Gener-ator should be checked out on your testbench. The DC adapter used to powerthe circuit should be capable of deliv-ering at least 11 volts DC into a 20 mAload, even at the lowest point in its out-put ripple. All but the smallest (100 mA)9 -volt adapters will suffice, and all 12 -

volt units con be used without excep-

The electret microphone element that's used to pick up audio from the piano is mountedto one end of a length of microphone cable and a phone jack is connected to the otherend.

Lion. Be sure the polarity is correct be-fore applying power.

Plug a set of stereo headphones intothe Auao jack: DO NOT use a mono-phonic set; the plug on mono sets willdestroy Q2 and Q3. Set S2 to the 103position, and advance the VOLUMEcontrol, R21, clockwise, You should heara tone whose pitch should changeslightly as you adjust R10, and noticea-bly as you adjust R11. The pitch will be-come ten times lower when you switchS2 to the Too position, and ten timeshigher when you switch to the 10position.

Connect a scope and a digital fre-quency counter to the output jacks,using 1:1 cables. If your scope has onlyone channel, connect J5 to the scope'sexternal trigger input. Set the gate timeof the counter to 1 second. Verify thatthe reading on the counter can be var-ied from less than 10,000 Hz to morethan 99,999 Hz by adjusting R11. If not,you can replace R12, which sets theupper frequency limit, with a smallervalue, or R13, which sets the lower limit,with a larger value.

Plug in the microphone and speakinto it, observing the output waveformon channel 1. The amplitude should beabout 2 volts peak -to -peak for a widerange of input amplitudes, althoughsome variation will occur. If the unitdoes not check out, go back and care-fully check all of the circuit connections,verifying that the voltages at variouspoints agree with those indicated onthe schematic. Correct any errors thatyou may find and verify that the prob-lem(s) have been solved, then move onto the phase of construction.

Operation. To tune a piano, the audiogenerator can be placed on thepiano, but the scope and frequencycounter need to be placed on a stand,within easy reach. I have found that aplatform of plywood, mounted to thetop of a camera tripod with a 1/4 -inchbolt, makes an excellent stand, The in-struments can be secured to the plat-form with a bolt, and adjusted to anyconvenient angle.

The microphone should be placed inclose proximity to the soundboard ofthe piano, in such a way so as to ex-clude ambient noise. A four -inchsquare of 2 -inch polyurethane foamserves that purpose well, if a hole isdrilled or punched through its centerand the microphone inserted nearly all

Aside from the audio generator, a few additional tools-a wrench (known in the trade asa tuning hammer ), and a pair of rubber wedges, or mutes, with wire handles --will beneeded to tune the piano. The mutes are inserted between the strings as necessary, sothat only one string at a time will sound when a key is struck.

the way through. The essential tools re-quired to adjust the tension of thestrings are a wrench (known in the tradeas a tuning hammer), and a pair ofrubber wedges, or mutes, with wirehandles. The mutes are inserted be-tween the strings as necessary, so thatonly one string at a time will soundwhen a key is struck. Those and otheruseful tools can be obtained from yourlocal piano supply house, which will belisted in the yellow pages. If there arenone in your area, you can order toolsfrom one of the supply houses listedelsewhere in this article under theheading of "Piano Supply Houses."

Before you attempt to tune yourpiano, you are urged to do some fur-ther reading. It is beyond the scope ofthis article to provide a course in piano -tuning. Many excellent books on pianotuning and repair have been written byskilled craftsmen, some of which canbe found in practically any library. (Seethe listing entitled "Suggested Read-ing").

Basically, the procedure to follow isfirst to set the audio generator to thefrequency of the note that you wish to

SUGGESTED READING

Electronic Piano TuningFloyd A. Stevens, Ph.D.Nelson -Hall, 1974

Piano Servicing, Tuning and RebuildingArthur A. ReblitzThe Vestal Press, 1976

Piano Tuning and Allied ArtsWilliam B. WhiteTuners Supply Co , 1978

tune. As an example, let's start with thenote on the keyboard that provides thereference pitch for all the other keys: Aabove middle C, which is the 49th keyon the keyboard, counting from key 1 atthe extreme left of the keyboard, and isdenoted A49. All the other keys aretuned relative to the pitch to which M9is tuned. The international standard forM9 is 440.00 Hz.

When settirg the pitch of the audiogenerator, switch S2 must be set for thecorrect range. For keys between G23and C64, S2 should be set to To. For keysC64 and above, S2 is set to the ioposition. For keys G23 and below, set S2to the icoo position. Once the correctrange is selected, adjust the COARSE andFINE frequency controls until the correctreading is displayed.

Once that is done, check channel 2of the scope for the presence of a 440Hz squarewave. and trigger the sweepto that waveform. Now switch to chan-nel 1, but leave the sweep locked tochannel 2. Mute two of the strings forthis note, so that only one string will vi-brate when the note is struck. Strike thekey, and observe the waveform onchannel 1. If the note is flat, or lowerthan 440 Hz, the waveform will move tothe right. If it is sharp, or higher than 440Hz, it will move to the left. The speed ofmotion will correspond to the degreeof sharpness or flatness.

As the tension of the string is adjustedto bring the note in tune, the waveformwill drift more slowly across the screen.For the best resolution, the sweepperiod should be adjusted to displaytwo or three complete cycles. Whenthe waveform is arrested, the string is in

tune. The mute can now be reposi-tioned, and the other two strings tunedthe same way.

The VCO will drift slightly during oper-ation. That is to be expected, and ismore noticeable during the first 30 min-utes. it isn't necessary to readjust theoscillator every time the least -signifi-cant -digit of the display drifts up ordown by a few counts, as that digit rep-resents more precision than is required.The least -significant -digit can be al-lowed to drift 4 before readjustmentis necessary.

if the pitch of the string is far removedfrom the setting of the VCO, the wave-form will move across the screen toorapidly for its direction of motion to beseen. In that case, adjust the frequencyof the VCO up or down as required toarrest the motion of the waveform. Thatwill tell you whether the pitch is sharp orflat. If M9 is flat by more than 20 cents(an explanation of this term follows), thepitch should not be adjusted to 440 Hz.

The 88 keys of the piano keyboardcomprise a little more than seven oc-taves, an octave being a doubling offrequency. See Table 1. In the Equal -Tempered Scale, each octave is divid-ed into 12 steps, called semitones, thatprogress upward in a geometric scale.Unlike channels in a radio band, whichare spaced in a linear scale an equalnumber of hertz apart, each semitoneis higher than the preceding one by afixed ratio. Since it takes twelve steps todouble the frequency, the ratio be-tween adjacent semitones is the twelfthroot of 2, or 1.0594631... --an irrationalnumber. Multiply 440 by that number,and you get 466,16, the pitch of the nextkey higher than 449. Multiply 440 by theinverse of this number (1/1.0594631),and you get 415.30, the pitch of the nextkey lower than 449 Notice that as yougo up the scale, the difference in hertzbetween adjacent keys becomes geo-metrically wider.

If the ratio between two pitches isother than an integer multiple of semi-tones, the cents unit is used. The cent isone -hundredth (1/1J0) of a semitone. It isalso a ratio, being the twelve -hun-dredth root of 2, or 1.000577807.... Thepitch of any key on the keyboard, rela-tive to A49, can be calculated from theratio

2 01200

where equals the absolute value in

TABLE 1 -THE EQUAL -TEMPERED SCALE

Note/Octave

Key# Hertz Stretchin Cents

Note/Octave

Key# Hertz Stretchin Cents

AJO 1 27.184 -20 F/4 45 349.03 - 1

Bb/O 2 28.817 -19 Gb/4 46 369.78 - 1

B/0 3 30.548 -18 G/4 47 391.77 - 1

C/1 4 32.384 -17 Ab/4 48 415.07 - 1

Db/1 5 34.329 -16 A/4 49 440.00 0D/1 6 36.391 -15 Bb/4 50 466.16 0Eb/1 7 38.578 -14 B/4 51 493.88 0E/1 8 40.895 -13 C/5 52 523.25 0F/1 9 43.352 -12 Db/5 53 554.37 0Gb/1 10 45.956 -11 D/5 54 587.33 0G/1 11 48.717 -10 Eb/5 55 622.61 + 1

Ab/1 12 51.644 - 9 E/5 56 659.64 + 1

A/1 13 54.746 8 F'5 57 698.86 + 1

Bb/1 14 58.035 - 7 Gb/5 58 740.42 + 1

B/1 15 61.522 - 6 G/5 59 784.44 + 1

C/2 16 65.180 - 6 Ab/5 60 831.57 + 2Db/2 17 69.096 5 A/5 61 881.02 + 2D/2 18 73.204 - 5 Bb/5 62 933.41 + 2E0/2 19 77.602 - 4 B/5 63 988.91 + 2E/2 20 82.217 4 C/6 64 1047.7 + 2F/2 21 87.106 4 Db/6 65 1110.7 + 3Gb/2 22 92.285 4 0/6 66 1176.7 + 3G/2 23 97.773 4 Eb/6 67 1246.7 + 3Ab/2 24 103.65 3 E/6 68 1321.6 + 4A/2 25 109.81 - 3 F/6 69 1400.1 + 4Bb/2 26 116.34 3 Gb/6 70 1484.3 + 5B/2 27 123.26 - 3 G/6 71 1572.5 + 5C/3 28 130.59 - 3 Ab/6 72 1667.0 + 6Db/3 29 138.35 3 A/6 73 1766.1 + 6D/3 30 146.58 3 Bb,'6 74 1872.2 + 7Eb/3 31 155.29 3 B/6 75 1984.7 + 8E/3 32 164.53 - 3 C/7 76 2103.9 + 9F/3 33 174.31 - 3 Db/7 77 2230.3 +10Gb/3 34 184.73 2.5 D/7 78 2230.2 +10G/3 35 195.71 - 2.5 Eb/7 79 2506.3 +12Ab/3 36 207.41 2 E/7 80 2656.9 +13A/3 37 219.75 - 2 F/7 81 2818.1 +15Bb/3 38 232.81 2 Gb/7 82 2989.2 +178/3 39 246.66 - 2 G/7 83 3170.6 +19C/4 40 261.32 2 Ab/7 84 3363.0 +21D b/4 41 276.86 2 AT7 85 3567.1 +23D/4 42 293.33 - 2 Bb/7 86 3783.6 +25Eb/4 43 310.86 - 1.5 B/7 87 4013.2 +27E/4 44 329.44 1 C/8 88 4259.2 +30

Standard pitch, A49= 440 HzValues shown are stretched for the average piano

tween A49 and the key in question.That's always the ratio of the higherpitch to the lower, so to calculate thepitch of a key higher than 449, simplymultiply the pitch of A49 by the calculated ratio. To calculate the pitch of anote lower than 449, multiply A49 bythe inverse of That ratio. For example, tocalculate the pitch of middle C (040).which is 9 semitones, or 900 cents,down from 449, multiply the value of449 (we'll use 440 Hz) by the inverse of 2to the 900/1200 power, or:

C40 - (440) 1/(2 900/1200) - 261,63 Hz

The calculated value would, of20 cents of the difference in pitch be- course, have been different for any val-

ue of M9 other than 440 Hz. Manypianos do not have 449 tuned to 440Hz. The reason for that is that when theyare first tuned at the factory, they areusually tuned a semitone lower, so thatthey will stay in tune longer during ship-ment and in the store. It takes a mini-mum of five tunings to bring the pianoup to standard pitch, each tuningbringing all the keys up by 20 cents, ifstep greater than 20 cents is at-tempted, the piano will not stay in tunefor long. Therefore, if you find a pianothat is still a semitone lower than stan-dard pitch, it is best to tune it to thatpitch, unless the owner wants it raised I

(Continued on page 11:)

VOLTAGEADAPTERfor your carIn just one evening, you can build a device to power your Discman, boombox,portable fridge, laptop computer, or any other device that requires 3, 6, or 9 volts,right from your car's cigarette lighter. It can even provide almost any DC voltage!

If you've got an older car without atape player or, more commonly,without a compact -disc player,

you might feel that you're missing outon something. And even if you've gotthose gizmos in your car now, yourtastes in music might not be the sameas those of your passengers. The mostcost-effective and diplomatic answerto both dilemmas is to use a portable,perhaps personal, sound system inyour car for you or your passenger. (Ofcourse a driver should not use head-phones; there are speakers on themarket that can plug into a personalaudio system and I strongly recom-mend using them in such circum-stances.)

By now you're probably saying"Cost effective? Batteries for porta-bles aren't cost effective." That's verytrue, and that's where the Car -PowerAdapter described in this articlecomes in. It's a small, unobtrusive de-vice that converts the 12 volts avail-able via your car's cigarette lighterinto 3, 6, or 9 volts. I'll also show youhow to modify the device to provideany DC voltage up to almost 12 volts.

The Car -Power Adapter can beused for many more things. My favor-ite use is as a power supply for mygarage -door opener transmitter. (I'll

never get stuck opening my garagedoor in the rain because the little bat-tery went dead.)

Of course there are devices like theCar -Power Adapter on the market,but they're pretty noticable in thedashboard and can get in the way ofother stuff there. They're also more ex-pensive and, of course, not configura-ble.

What's in It?. The Car -Power Adapt-er contains an LM317 adjustable -volt-age regulator. Its output voltage isdetermined by the resistor networkaccompanying it. Take a look at theexample circuit in Fig. 1. Resistors RAand 12, set the regulator's output volt-age according to the following equa-tion:

VOUT = Vref (1 RB/RA) + lacijRA

In most applications, Vref (which is thevoltage across RA) is 1.25 volts and 101is about 50 pA. Those values make theequation:

Vow = 1.25(1 + RB/RA)

which is the equation that you shoulduse if you want different output volt-ages than the ones presented here.

The Car -Power Adapter circuit isshown in Fig. 2. In the circuit, the role ofRA is played by R2. Resistors R1, R3, andR4 perform the function of RB and actas follows: If the single -pole double -throw center -off switch (S1) is in thecenter position, only R2 and R1 are inthe circuit. They program the reg-

ulator to output 9 volts. Switching S1 toput R3 in the circuit causes the resis-tance between the adjust terminaland ground to drop. The effective re-sistance of the R1/R3 parallel com-bination sets he regulator to output 3volts. Similarly, with R4 in parallel withR1, the output voltage is 6 volts.

Circuit Construction. Although theCar -Power Adapter is not a critical cir-cuit, you should pay special attentionto the following instructions becauseof the compactness required. Oneother thing that deserves mention isthat the instructions are for negative -ground car wiring. If you've got apositive -ground vehicle, switch all theconnections between the lighterplug's ground clip (mentioned later)and its center contact.

Start by sawing the heat sink off ofthe LM317 regulator. The heat sink willnot be necessary because of the lowcurrents required by most low -voltagedevices. The heat sink will only makethe device impossible to fit in the light-er plug, so carefully get rid of it.

For the rest of the assembly take alook at Fig. 3 (which, with the excep-tion of the plugs and the switch, repre-sents the physical, layout of thecircuit). Wrap one lead of R2 aroundthe LM317's center terminal as shown.Lay the resistor directly on the reg-ulator leaving rocm for R1 as shown.

INPUTVOLTAGE

OUTPUTVOLTAGE

Vow;

Fig. I. This is the standard way ofwiring an LM3I7 adjustable -voltageregulator. The output voltage isdetermined by the values of RA and R8.

PL1

ADJ

OUTPUT

INPUT

LM317

LM317

Wrap a piece of electrical tapeover resistors R2, R3, R4, and the longlead of R2. The tape will insulate R2'slong lead from R1. Now place R1 nextto R2. Wrap another piece of tapeover the end of the regulator wherethe heat sink was to cover that sawed-off terminal. Now its time to bundle upthe assembly with some wide heat -shrink tubing. Make sure that ifs longenough to wrap around the edges of

R2

240f2 PL2

R1

R3 R4

470i29V

2.4K

3V 6V

1.5K S1

Fig. 2. In the schematic diagram for the Car -Power Adapter, note how the value of RB(which is RI with SI in the center position) is changed by putting R3 or R4 in parallelwith RI.

Wrap the remaining lead around theadjust terminal leaving no slack in thelead. Solder both ends of R2 to theirrespective terminals.

Take six pieces of stranded wireabout 5/8 -inch long, strip off 3/46 -inch ofinsulation from one end of each, andtin that end. I suggest you use differentcolors for easy identification. Solderone of them to the LM317's center ter-minal, close to the regulator's body,and trim the terminal as short as possi-ble. Use a small piece of heat -shrinktubing to insulate the connection.(Don't worry if you do not have a heat-shrink gun; a blow dryer will do.) Takeanother piece of prepared wire andsolder it to the input terminal, againtrimming the terminal short and usingheat -shrink tubing.

Take another piece of tinned wireand solder it close to the body of R3.Use a piece of heat -shrink tubing toinsulate the connection, but don't slipit over the end of the resistor-that willmake it too bulky. Repeat the pro-cedure for R1 and R4, but use twopieces of wire on one end of R1.

Lay R3 next to R2, wrap its free leadaround the lead of R2 as shown, andsolder the connection. Follow thesame procedure to connect R4 to R3.Now connect the free end of R1 toR2, but don't lay it next to R2 just yet.

the regulator. Shrink the tubing andtrim the excess. You should have acompact package with wires comingout one side.

Strip 3/46 -inch of insulation off theends of the wires from R3, R4, and oneof the wires from R1. Strip Y8 -inch offthe remaining ends of the other threewires and tin them all.

Final Assembly. Before putting ev-erything together, you must first pre-pare the switch and case (which is thecigarette -lighter plug). You have to ex-pand the hole in the back end of thecigarette -lighter plug for the switch tofit through it. You can do that easily bytwisting a triangular hand file aroundin the hole until it's large enough toaccommodate the switch's threads.

You also have to grind down theplastic sides of the switch to fit it in thecigarette -lighter plug. You can use ahand file or power grinder. If you use apower grinder, go slow-the plasticturns to powder very quickly. Your goalis to take enough off of the sides of theswitch to allow it to enter the plug andseat firmly against the rear. Be sure toleave enough plastic around the out-side terminals to prevent them frombreaking off.

Now you must determine where todrill the hole for the power cord, which

PARTS LIST FOR THECAR -POWER ADAPTER

RESISTORS ( All resistors are 1/4 -watt,5% units.)

RI -1500 -ohmR2 -240 -ohmR3---470-ohmR4--2400-ohm

ADDITIONAL PARTS ANDMATERIALS

U I ---LM 3 l 7 I -amp adjustable -voltageregulator, integrated circuit

PLI-Cigarette-lighter plugPL2-See textHeat -shrink tubing, stranded wire,

coax, electrical tape, solder, etc.

should be a coax type to prevent in-ductive pickup of noise. Put the switchin position inside the cigarette -lighterplug and measure the distance fromthe front of the case (the end that isinserted into the dashboard) to theterminals on the switch. Use the mea-surement to help you drill a hole forthe power cord so the cord can enterwithout interference from the switch.About 1/2 -inch from the end with theswitch worked well for me. Removethe switch and drill the hole for thepower cord large enough to looselyaccommodate the coax power linethat you use.

Connect the wire with the'/,6-inchlead from R1 to the spring clip thatconnects the cigarette -lighter plug toground. Connect the remaining wirefrom R1 to the center contact of S1.Connect the wires from R3 and R4 tothe remaining terminals on the switch,as indicated in Fig. 3.

Solder the wire from the regulator'sinput terminal to the center terminalon the cigarette -lighter plug. Run thepower -cord coax through the holeyou made for it and solder its shieldingto the ground clip. Slip a small pieceof heat -shrink tubing over the wirefrom the regulator's center terminaland solder the coax's center conduc-tor to the wire. Position the tubing ovethe joint and shrink it.

Position the ground clip so that itsurrounds the regulator. As a fincltouch, you might want to slip someheat -shrink tubing over the wires so:-dered to the clip to provide somestrain relief. The tubing should be pod-tioned to hold a bit of the wire's insula-tion tightly against the clip.


hen weneed to lo-cate an ob-

ject, the first sense that weuse is sight. Well, with theTracking Transmitter de-scribed in this article, you canalso use your hearing. TheTracking Transmitter outputsa series of short, tone -modu-lated pulses that can bepicked up on almost any FM re-ceiver, as a recognizable beep.Using an FM receiver (eithermobile or portable), one can scoutareas where you might expect theobject to be located.

When the transmitted signal isdetected, simply varying the posi-tion of the receiver will cause the re-ceived signal strength to increase ordecrease, enabling you to determinethe general direction of the signal. Bycontinuing to scan the area, youshould soon be able to pinpoint thelocation of the object.

Circuit Description. The TrackingTransmitter (see the block diagram inFig. 1) is a fairly simple circuit consistingof four distinct sub -assemblies; a free -running multivibrator, a transmitswitch, an audio -tone generator, andan FM transmitter. The multivibrator isused to control the transmit switch,which turns both the audio generatorand the transmitter on and off at agiven rate. That helps to reducepower consumption to a bare mini-mum. The output of the audio gener-ator is fed to the FM transmitter, whichputs out a periodic beep in the 88- to108 -MHz range that can be detectedusing an ordinary FM receiver.

A schematic diagram of the Track-ing Transmitter is shown in Fig. 2. Themultivibrator is comprised of compo-nents 01, 02, C1, C2, and R1 throughR4. The values of R2 and R3 havebeen chosen to produce a pulsewidth of 300 milliseconds with a pulseseparation of 1500 milliseconds. Theoutput of the multivibrator, which istaken from the collector of 02, is cou-pled through R5 to the base of 03. Theoutput of Q3, taken at its emitter, isused to drive Q4. Together those two

This little circuit can helpyou to find your car in a

packed parking lot; locatea child who has

disappeared in a crowd; orreunite you with a dog thathas escaped the confinesand safety of your yard.

BY VINCENT VOLLONO

transistors (03 and 04) form the trans-mit switch.

When the output of the multi -vibrator swings positive, 03 turns on,which then turns Q4 on. With Q4 on,the emitter of Q6 is pulled to ground,causing it to conduct. With 06 con-ducting, any signal applied to its baseis transferred to the antenna, which isconnected to the junction formed byC8 and C9. Components Q5, R6, R7,R8, and C3 make up the audio -tonegenerator, whose output is coupled tothe base of Q6 through C4 and R8.

During the negative alternation of

the multivibrator output,03 and 04 turn off,

which also turns offthe transmitter. Com-

ponents Q6, R10, R11,R12, L1, L2, and C5

through C9 comprise thecircuit's transmitter section,which operates from below 88MHz to above 108 MHz.Capacitor C7 is used to

coarse tune the transmitter, whileC6 (which is optional and can beleff out of the circuit) is used to fine

tune it. The antenna for this project isnothing more than a 6- to 12 -inch

length of stranded insulated wire at-tached to the appropriate point inthe circuit.

The Tracking Transmitter is de-signed to operate from a 9 -

volt battery; however, it willalso operate from voltagesranging from 5 to 18 volts.

The higher voltages wouldproduce the, most powerful output

signals.

Circuit Construction. The layout forthe Tracking Transmitter is fairly com-pact. The circuit board measures only21/2 -inches long by 13/16 -inches wide(see Fig. 3). Wnen building the Track-ing Transmitter, it is important that allleads be kept as short as possible toavoid any unwanted capacitances.You must also avoid any looping of thecomponent leads to limit unwantedinductances.

All of the components, with the ex-ception of the battery supply, aremounted on the printed -circuitboard. Install all of the board -mounted components using Fig. 4 asa guide. Be sure to double-check alltransistor pinouts before mountingthose units.

Note that all of the axial -lead com-ponents (R1 thrcugh R12 and L1) arevertically mounted. The electrolyticcapacitors should be miniature radi-al -lead units. If axial -lead electrolyticsare used, they must also be mountedvertically and be miniature types.

Note that inductor L2 is a hand -wound, air -core coil, consisting ofseven turns of #22 solid magnet wire.

ANTENNA

MULTIVIBRATOR h SWITCHTRANSMIT

01 02 '-VAUDIO

TONE GENERATOR

05-1122121111

88 TO 108 MHzFM TRANSMITTER

O6

Fig. I. The Tracking Transmitter consists of four distinct subassemblies; a free -runningmultivibrator, a transmit switch, an audio -tone generator, and an FM transmitter.

B11+9V

100KR6 $ R7 R10

1K 330R81K

L1 G6 C7 R112.2pH 1.5 -3pF 1 0- 50pF 10K

C5 T L2.01 SEE TEXT

R91K

R2 R1

180K 6.8K

C1

10

R3 R4391( 6.8K

03R5 PN2222

10K

C2

PN2222 10 1%

Q2PN2222 CiO

PN222204

06PN2222

R124.7K

C8

C927pF

Fig. 2. The multivibrator (which produces a pulsewidth of 300 milliseconds with apulse separation of 1500 milliseconds) is built around QI and Q2. The multivibratoroutput is coupled through R5 to the base of Q3, whose emitter feeds Q4, whichcontrols the circuit's transmitter section.

21/2 INCHES

Fig. 3. The Tracking Transmitter was assembled on a small printed -circuit board,measuring only 21/2 -inches long by13/16-inches wide. Because of its size, the axial -leadcomponents (all resistors and LI) must be mounted vertically.

B1 I

ANTI

-L1- -C8- -C9--R12-

R51

-05 -C1 \ G3

R31 1R4 UV R6 R11L2

E)C6

C7

Fig. 4. All of the components, with the exception of the battery supply are mounted onthe board. Install all of the board -mounted components using this diagram as a guide.

PARTS LIST FOR THETRACKING TRANSMITTER

SEMICONDUCTORSQI-Q4. Q6-PN2222 general-

purpose NPN silicon transistorQ5 -2N2646 N -channel unijunction

transistor

RESISTORS(All resistors are 1/4 -watt. 5%. units.)RI, R4 -6800 -ohmR2 -180,000 -ohmR3 -39,000 -ohmR5, R I I -10,000 -ohmR6 -100,000 -ohmR7 -R9 -1000 -ohmR10 -33 -ohmR12 -4700 -ohm

CAPACITORSCl, C2, C4 -10 -)LE 16-WVDC,

miniature radial -lead ElectrolyticC3, C5-.01 -µF, ceramic -discC6-1.5- to 3-pF miniature variableC7-I0- to 50-pF miniature variableC8, C9-27-pF, ceramic -disc


LI-2.2-µ,H coilL2-See textANTI-See textPrinted -circuit board materials, #22

magnet wire, '/.12 -inch drill bit (seetext). 9 -volt transistor -radio battery,battery connector, enclosure(optional), on/off switch (optional)wire. solder, hardware. etc.

Note: The following items areavailable from Xandi Electronics,PO. 25647, Tempe. AR85285-5647; Tel. 602-829-8152(catalogs and general information)or 800-336-7389 (orders only). Acomplete parts kit (#XTRIOOKB)for $28.90 + $3.00 Sill,containing an etched and drilledprinted -circuit hoard, all resistors,capacitors. inductors, transistors,and battery snap. COD orders, add$6.00. Arizona residents add 6.7%sales tax.

That coil is made by carefully wrap-ping 7 turns of the specified wire on a5/32 -inch drill bit. Once wound, scrapethe insulation off of each end of thecoil and insert the ends into the ap-propriate holes in the printed -circuitboard, and solder it into place; makesure that you have a good electricalconnection. Once the coil is formedand installed on the circuit board, youmust be careful not to move the coil,or the windings may accidentally


UNIVERSAL RS-232CONNECTORBY JAMES E. TARCHINSKI

The RS -232 serial communica-tions standard is the electronicequivalent of Rubik's Cube.

When you set out on a venture to con-nect two RS -232 devices, there is noobvious path to get from your startingpoint to where you want to be. But justlike that insidious little cube, if you fid-dle around with the devices longenough, you can generally arrive atyour objective. Armed with the Univer-sal RS -232 Connector described inthis article, a little knowledge, and alittle patience, you should be able togreatly shorten your journeys downthe often bumpy RS -232 road.

The Universal Connector is a simple,one -evening project. It is essentially adedicated break-out board thatmakes the important RS -232 signalseasily accessible and reconfigurea-ble. With it, you can debug a commu-nications link by testing a multitude ofdifferent pin configurations veryquickly. It saves you the time and trou-ble of wiring numerous "permanent'cables before you find the magicalcombination that will allow the twodevices to talk to one another. Beforediscussing the Universal Connectorand its construction in detail, however,let's first look at some of the causes ofRS -232 -phobia.

The Root of the RS -232 Problem.There are many reasons why con-necting two devices by the RS -232

This inexpensive one -eveningproject can save you hours of labor

spent connecting RS -232 devices.

protocol can be such a headache.First of all, no computer or peripheralmanufacturer follows the true andcomplete standard! Of the 25 pins inthe protocol's standard D -type con-nector, only three are not assignedfunctions. And of the 22 pins that dohave assignments, in five years ofsearching the author has yet to en-counter a piece of equipment thatuses any more than eight of them. Thisis, of course, the reason why the indus-try is now moving to a 9 -pin, D -con-nector version of the RS -232 stan-dard-the complexity detailed in theoriginal specification is not neededwith today's electronics.

Another main source of RS -232 ag-gravation is the generally poor docu-mentation that comes with moderncomputers and peripherals. Mostmanuals now days are written fornon -technical usdrs, people who nei-ther know nor care to know the dif-ference between a transmit signaland a receive signal. Those who docare about such things are forced tofind other reservoirs of information be-sides the owner's manuals. Or, moreoften, they simply resort to the time -proven method of trial -and -error wir-ing.

A third cause of RS -232 connectionproblems, one that is really more ablessing than it is a curse, is the shearnumber of devices that have the abil-ity to communicate via RS -232. Be-

cause there is such a vast assortmentof computers, printers, plotters, scan-ners, and such on the market today,there would be no way to fully docu-ment all the possible interconnec-tions. People are therefore often leftto fend for themselves. This situation isfurther complicated by the fact thatdifferent software packages some-times require different signals to bepresent on the RS -232 cable beforethey will operate properly.

The Universal Connector. Figure 1 isa schematic diagram of the unit. It

consists of two 25 -pin, D connectors,each wired to a series of small sol-derless circuit board sections. To test aprototype cable design with the Uni-versal Connector, all you need to do isconnect one device to each side ofthe Universal Connector and then usesmall jumper wires to test different pinlinkages. You'll no longer need to sol-der and unsolder countless pins to de-bug an RS -232 junction.

Note that not all of the 25 pins areused for the unit, this being a result ofthe market's trend to the "abbrevi-ated' RS -232 standard mentionedpreviously. Table 1 lists the names ofthe eight RS -232 lines that are used inthis project. Although some of theolder devices may use some of theother 17 pins, the vast majority of to-day's devices can be connected withsome combination of the eight lines

PL1

14

2 0 0 0 0-15

0 0 0 0TB1

16

4 0 0 0 017 TB2

0 0 0 018

6 0 0 0 019

0 0 0 0 TB3

20

8 0 0 0 021

0 0 0 0TB4

TB5

TB6

TB7

TB8

0 0 0 00 0 0 0

14

,S01O

2

0 0 0 00 0 0 0

15

3

16

4

0 0 0 00 0 0 0

17

00

Oo

O0

5

18

6

0 0 0 00 0 0 0

19

7

20

OO

o-c)

Oo

8

21

OOO

Fig. 1. The schematic for the Universal Connector reveals the simplicity of the project,but not its usefulness in debugging RS -232 interfaces.

TABLE 1-IMPORTANT SIGNALS

Signal Name Abrevlation Pin

Transmit Data TX 2Receive Data RX 3

Request To Send RTS 4

Clear To Send CTS 5Data Set Ready DSR 6Signal Ground GND 7

Data -Carrier Detect OCD 8Data Terminal Ready DTR 20

used by the universal connector. If youthink you'll need to interface with anyof those older devices, you may wantto wire in some additional solderlesscircuit -board sections in your versionof the project.

Construction. Being fairly simple,

a

a

this is an excellent project to learn touse the "iron -on PC pattern method"of board construction detailed in theJuly, 1990 issue of Popular Elec-tronics. Another reason this project isan ideal candidate for the iron -onmethod has to do with the circuit'ssymmetry. Because of its inherent sym-metry, the foil pattern given in Fig. 2 isthe same as its mirror image-sothere is no need to photocopy thepattern twice to obtain an invertedimage.

Before you stuff the board, though,you should decide whether or notyou'll want to install the finished unit inan enclosure. To facilitate easy accessto all the tie -blocks, no enclosure wasused for the author's prototype. In-stead, rubber feet were placed on the

t71=lii

11:71_7°O

a

41/4 INCHES

Fig. 2. This artwork can be copied onto translucent plastic for photographic boardfabrication, or it can be easily duplicated directly on the PCB for the direct etchmethod.

bottom of the PC board to preventany accidental shorting of the boardtraces.

If you would like a more finishedversion of the Universal Connector, anenclosure would certainly be in order.One method worth considering is touse the "bottom" of a polystyrene en-closure. Such an enclosure could beconfigured so that the two D -con-nectors stick out through holes in op-posing ends of the case, and the topcould be quickly removed for accessto the tie -block array.

PL1

TB1

TB2

TB3

TB5

TB6

TB7

TB8

SO1

Fig. 3. The only important thing to keepin mind when stuffing the board is to placethe male connector .11 (and thus the femaleconnector J2) into the right set of holes onthe board.

PARTS LIST FOR THERS -232 UNIVERSAL

CONNECTOR

TBI-TB8--2 x 4 -hole solderlesscircuit -board sections

Jl-25-pin, male D -connector12 -25 -pin, female D -connectorPrinted -circuit board materials,

project enclosure, labeling kit,solder, etc.

Another important point to bemade about the circuit is that oneconnector of each gender is used,and their placement is important.That may sound like a trivial point, butit could cost you hours of frustration itnot attended to. Suppose, for exam-ple, you were to install Iwo male con-nectors from your scrap box on aboard made with the foil patterngiven. Because the same genderswere used, the pin numbers from thetwo connectors would not be aligned,and you would not be connecting thepins you thought you were.

With these simple considerations,you should be able to build your ownUniversal Connector easily enough.Once completed, it should simplifyyour next RS -232 job so you can moveon to better things.

Here is a circuit that

leaves no doubt as to

whether someone

has been trying

to reach

you

BY STEVEN M. O'KELLEY

Recently, telephone com-panies began offering anew type of service; Elec-

tronic Voice Mail. Intended as areplacement for the answeringmachine, the service leaves agreeting and records messagesfrom callers when a subscriber isunable to answer the phone. Typ-ically, Voice Mail is activated aftera preset number of rings to allowsubscribers time to answer a callwhen they are at home.

Instead of using magnetic record-ng tape, the service records andstores the caller's message in digitalform at the telephone -switching of-fice. The user can then retrieve mes-sages using any Touch Tone tele-phone.

Even though Voice Mail has somenice advantages over its mechanicalcounterpart, there is still some roomfor ;mprovement, For example, whena message has been left, the systemlets you know by pulsing the first fewseconds of dial tone when you pickup the handset. That means thatsomeone who is in and out severaltimes a day has to pick up the phone'each time to check for messages.

Wniie a device that automaticallydoes this would be complex, the nextbest thing is easy. The simple circuitdubbed the Tel described inthis article will detect when someonehas called and flash an LED to alertyou to check for messages.

How it Works. A schematic diagramof the Tel -Tale is shown in Fig. 1. Thecircuit is built around a couple of low-cost IC's, an H11C4 optoisolatoricou-pler with an SCR output (U1) and anLM39C9 LED flasher (U2). The circuit is

Voice -Mail Alertconnected to the phone line's tip(green) and ring (red) wires in thesame manner as any extensionphone.

When the phone is on hook, there isabout 48 volts DC across the line. Aneon lamp (NE1) is connected in se-ries with the tip conductor. BecauseNE1 requires about 60 volts to con-duct, the circuit represents a high im-pedance to the line and no currentflows. When a call is made to the cov-ered line, a ring voltage- -about 90volts AC at 20 Hz is applied to thetelephone line by the telephone -switching office. During half of the cy-cle, current flows from the ring linethrough R1, D1, NE1, and C1 to the tipline. During the other half cycle, thecurrent reverses and the LED portionof U1 conducts, triggering its internalSCR, allowing a small amount of cur-rent to flow through the SCR and R2.That current flow causes capacitor C2to begin charging.

Integrated circuit U2 and capacitorC3 form a simple LED -flasher circuitthat will operate on just over a volt,When the charge on C2 reaches the1 -volt level, U2 flashes LED1 and thecharging cycle of C2 starts over. TheLED continues to flash until S1 (reset) ispressed, Closing S1 deprives the SCRof holding current, thereby turning it

off. The Tel -Tale remains in that stateuntil re -triggered by the next in -com-ing phone ca:..

Construction. The prototype of theTel -Tale was assembled on a smallprintedcircu t board, measuringabout 1% inches square. A templateof the author's PC pattern is shown inFig. 2. Note that in that diagram, onlyone set of IC pads (near the center ofthe board) are shown; the reason forthat will become apparent in a mo-ment.

Once you've etched your boardand gathered at the parts listed in theParts List, construction can begin. Aparts -placement diagram for the Tel -Tale's printed -circuit board is shown inFig. 3. In the author's prototype, a sin-gle 16 -pin IC socket is used for both U1and U2 (6- and 8-oin devices, respec-tively). You can do the same thing, or, ifyou happen to have 6- and 8 -pinsockets on hand, you can use individ-ual sockets. In any event, using socketsprevents damage to the 1C's duringsoldering, and makes replacing ei Cher IC (should the need arise) simpler

Once the IC socket (or sockets) is inplace, install the rest of the compo-nents as shown in Fig. 3. Note thatbecause of tight spacing R1, R2. andD1 were vertically mounted to the cir-

TO

TEL

LINE

R1

4.7KR 0- -MN -D1

1N4007

NE1NE -2

U1

H11C4

6

NC

C2220

R2 B1

56K 9V

S1 C3220

LM3909

ft

Fig. I. The Tel -Tale is built around a couple of low-cost IC's: an HI/C4 optoisolatorlcoupler with an SCR output (UI) and an LM3909 LED flasher (U2), and is connectedto the phone line in the same manner as any extension phone.

15/8

Fig. 2. The prototype of the Tel -Tale wasassembled on a small printed -circuitboard, measuring about Ns inchessquare, a full-size template of which isshown here.

TO

TELEPHONELINE

T () R

F11

Y00co D1

o -14-zQ

cnI O.

NE1

R2

U1C1

LED1

U2

-C3- -4-

d2

Fig. 3. Once you've etched your boardco and gathered all the parts listed in the

Parts List, construction can begin,cn guided by this parts -placement diagram.

In the author's prototype, a single /6 -pinIC socket is used for both UI and U2 (6-=and 8 -pin devices, respectively).

w-JL1J cult board. When installing LED1, leave

the leads long enough so that its lenswill stick through a hole in the circuit's

28 enclosure.

Here's the author's completed prototype.

The author's prototype was housedin a plastic Radio Shack enclosure(catalog number 270-293), whichprovides ample room for the circuitboard and also has a built in batterycompartment. The circuit board canbe mounted using a small piece ofdouble -sided tape. Switch S1 (either apushbutton- or a toggle -type mo-mentary single -pole unit) mounts tothe case. Because the battery drain islow (about 0.3 mA), the authorelected not to use an on/off switch inthe design of this circuit

If you have one of the older desk- orwall -type telephones, you may findthat there is ample room to mount the

The circuit can be mounted in a plasticproject box or even within sometelephones.

PARTS LIST FOR THETEL -TALE

SEMICONDUCTORSUI-H11C4 or NTE3046

optoisolator/coupler with SCRoutput, integrated circuit

U2-LM3909 or NTE876 LEDflasher, integrated circuit

DI-IN4007 I -amp, 1000 -Ply,rectifier diode

LEDI-Super-bright LED (RadioShack 276-087)

RESISTORS(All resistors are 1/4 -watt, 5% units.)R l -4700 -ohmR2 -56,000 -ohm

CAPACITORSCI -1-µF 200-WVDC, metallized -

filmC2, C3-220-ILF, l0-WVDC,

electrolytic


SI-SPST momentary -contact toggleor pushbutton switch

BI -9 -volt transistor -radio batteryNEI-NE-2 neon lampPrinted -circuit board materials,

enclosure, battery holder andconnector, telephone wire, solder,hardware, etc.

circuit board and battery inside.Mount LED1 to the case of the phoneand use a few inches of wire to con-nect it to the circuit. Most such phonesalso have a hook switch with unusedcontacts that can be used for S1. Byusing the hook -switch scheme, the cir-cuit will reset itself whenever you usethat phone.

Installation. With your circuit com-pleted, connect it to the phone lineusing standard quad telephone wireor a modular cord. The tip and ringinputs of the unit connect to the greenand red wires, respectively, inside thetelephone outlet. The Tel -Tale shouldbe mounted so that the LED can beeasily seen. The LED radiates most ofits light in a narrow pattern so youshould be looking into the top of theLED. The next time you are called, thecircuit will flash. Even if you don't haveVoice Mail, you may find this devicehandy. It will always let you know thatsomeone has tried to reach you.

The IncredibleHot Canaries

This novel circuit will emulate the sounds of two birds singing together in a way thatwill intrigue you. They start slowly and then sing rapidly increasing trills as they

compete with each other for virtuoso supremacy.

Do you love the song of birdsaround your home, but hate theidea of caging birds? Perhaps

you can't stand the thought of cleaningout the cage-birds can be messy littlecritters. Whatever the reason for not in-viting our feathered friends into yourhome, you can still enjoy their melodicsongs by building this electronic bird -song circuit. The dual -bird melody pro-duced by this project will both entertainand amaze your friends, and when youdon't feel like listening to them, you cansimply turn them off.

The idea of producing artificial birdsongs is not new; artificially producedbird song has been used in clocks dat-ing back several centuries. And manybird -song circuits have been devised inthe last decade or so. But it's been awhile since we've seen or heard of anynew arrivals, so we thought, "Why notbuild a new circuit'?"

We could have been really cleverand built the unit into a fancy gilt cage

This story first appeared in Silicon Chip, Aus-tralia (February, 1990); reprinted with permis-sion.

complete with an ornamental bird. In-stead, we built the circuit into a stan-dard project box, bedecked with acouple of ornamental birds-and dub-bed it Hot Canaries.

Using just two garden-variety IC's anda handful of resistors, capacitors, andother support components, our circuitcan emulate the sound of two canarieshappily chirping and trilling away. Theperiod of tilling and chirping, and thepitch of each bird is different, creatinga random effect as the birds come inand out of chorus.

One of the problems of producingsuch a bird -song circuit is that so manyparameters have to be controlled-the pitch, rate of chirps and trills, andthe duration of the trills. Such a circuittends to be very complicated becausecertain sections of the circuit will haveto perform more than one function. Ourapproach was to try and come up witha good compromise-produce an un-complicated circuit that would also bereasonably easy to build and trou-bleshoot if necessary, while beingpowered from a battery.

About the Circuit. Figure 1 is a com-plete schematic diagram of the circuit,which is built around two LM324 quadop -amps. Essentially, the circuit consistsof 7 oscillators connected in such amanner so as to emulate the sound ofIwo canaries singing. One oscillator(built around U' -a) serves as a switchingcontrol, which turns the canary soundsoff for a short while after a minute or soof chirping.

The remaining six oscillators make uptwo almost identical circuits-consist-ing of U1-d/U1-c/U2-c and U1-b/U2-a/U2-b-whose outputs are mixed to-gether and amplified by a single tran-sistor that is used to drive a smallspeaker. The circuits differ only in thevalues of two pairs of capacitors-C2/C3 and C8/C9.

Each op -amp is configured forSchmitt -trigger operation by the resistorconnected between its output and itsnon -inverting input. Each Schmitt trig-ger was then mode to operate as anoscillator by connecting a resistor/ca-pacitor network between its output andinverting input. Voltage -divider net - 29

R3668K 7'

+ 9V

+ 9V

R5

50K

12

Cl I 1N4148D1

100'.N R3

470K'AN

R37 t33K

+ 9V

U1 a

1/4 LM324

R4

100K

+ 9V

S1

POWERO 1

-:74rC10

B1 47+9V

I

+9V

R650K

BC328VIEWED FROM

BELOW

R7

47K

14

3

1/4 LM324R11

15K 33K

+9V

R1368K

10

- C31000

CHIRP CONTROLOSCILLATOR A

D2

1N4148

R847KAM

R19100K

1/4 LM324

U1 -c

47K

11

-zR17 R21 R25=. R14 3.3K 470K

8

C4

.001

+9V

R2468K

1/4 LM324 R915K4 R12

33K

33K

R23180K

4s1

C547

CHIRP OSCILLATOR A

L_ R3068K

C8

330pF T R1 t10K ?'

TONE OSCILLATOR A

+ 9V

R1568K 4

R20100K

--.~3 -

C2 -470 2

CHIRP CONTROL

OSCILLATOR B

+9V

41/4

LM324

U2 -a

47KR18

33K+ C7T 47

CHIRP OSCILLATOR B

11

Fig. 1. Hot Canaries is a combination of seven Schmitt -trigger oscillators (built from twoLM324 quad op -amps). One oscillator serves as an onloff control, the six other oscillatorsgenerate the sounds of two canaries.

PARTS LIST FOR HOT CANARIES

SEMICONDUCTORSUl, U2-LM324 quad low -power op -

amp, integrated circuitQl-BC328, ECC-159, or equivalent,

PNP silicon transistorDl, D2 -1N914, 1N4148, or equivalent

small -signal silicon diode

RESISTORS(All fixed resistors are 1/4 -watt, 5%

units.)RI, R2 -10,000 -ohmR3, R25, R28, R32, R34 -470,000 -

ohmR4, R19, R20, R31, R33 -100,000 -ohmR5, R6 -50.000 -ohm miniature PC

mount trimmer potentiometerR7, R8, R17, R18 -47,000 -ohmR9, R10 -15,000 -ohmR11, RI2, R14, R16, R37 -33,000 -ohmR13, R15, R24, R27, R29, R30, R36-

68,000 -ohm

R21, R22 -3300 -ohmR23, R26 -I80,000 -ohmR35 -33 -ohm

CAPACITORSC1 -100-µF, l6-WVDC, electrolyticC2 -470-µF, 16-WVDC, electrolyticC3 -1000µF, I6-WVDC, electrolyticC4, C6 -0.001-µF, metallized polyesterC5, C7, C10-47-10, I6-WVDC,

electrolyticC8-330-pF, ceramic or polystyreneC9-270-pF, ceramic or polystyrene

ADDMONAL PARTS AND MATERIALSSPKR1-8-ohm speakerS1--SPDT toggle switchB1 -9 -volt transistor -radio batteryPrinted -circuit board materials,

enclosure, 9 -volt battery holder andconnector, wire, solder, etc.

R223.3K

R31

100K146

1/4 LM324

U2 -c8

R32470K

4M

+ 9V

SPKR18i2

.001 180K 10KR2 01

8C328C6 R26

)1--AAN

+9V R33100K

R2768K

R28470K

-- 1/4 LM324

U2 -b7

Illar R34

=68K

470K

WsC9

270pF I TONE OSCILLATOR B

R353313

MIXEDOUTPUT

works, consisting of R13/R14 and R24/R30 for the upper half of the circuit, andR15/R16 and R27/R29 for the lower half,set the upper and lower thresholds ofthe chirp and tone oscillators.

Each oscillator then works as follows:When power is first applied, the capaci-tor at the inverting input has no voltageacross it and the op -amp's output ishigh. The capacitor starts to charge viaits associated resistor until it reaches thethreshold level set at the non -invertinginput.

When the charge on the capacitorequals the reference, the op -amp out-put goes low and the capacitor beginsto discharge until it reaches the lowerthreshold voltage. When the lowerthreshold is reached, the op -amp's out-put again swings high and the cyclebegins again, producing an approxi-mate square -wave at the oscillator'soutput. That signal is then fed across aresistor/capacitor network, producing a

41/4 INCHES

Fig. 2. Here's an actual -size foil pattern for Hot Canaries' printed -circuit board.

sawtooth waveform that is applied tothe inverting input.

Now that we've discussed the basicoperation of the individual oscillators,let's see how those oscillators interactwith each other to produce bird a song.

Oscillator Interaction. To understandthe interaction of the oscillators thatproduce the canary sounds, let's firstlook at U2-b-the last op -amp in thelower bird -song circuit-which is la-belled as a "tone oscillator." Its basicfrequency is set at around 2-3 kHz. Notethat if R26 and R34 (which tie the os-cillator output to other parts of the cir-cuit) were removed, U2 -b would justoscillate continuously at around 3 kHzor so. However, it wouldn't sound muchlike a canary.

To produce a chirping affect, U2 -b is

B1

-R10 ---F17----

131

"TO/4-

R3 I ciF17 I R4

-R36-

-R11 --

Lit

C2

C10

modulated at a rate that starts at about1 Hz and rises until U2 -b runs continu-ously. The "chirp" frequency is gener-ated by U2 -a. To get the chirpfrequency to rise, U2 -a is controlled by alower -frequency oscillator, U1 -b (thechirp -control oscillator). As the voltageacross C2 increases, the chirp frequen-cy rises. When the chirp oscillator risesto its highest value, an RC network, con-sisting of R26 and C6 connected be-tween pins 7 of U2 -b and 2 of U2 -a,causes the two oscillators to modulateeach other so that the output of U2 -b"warbles" just like a canary.

The circuit formed by op -amps U1 -c,U1 -d, and U2-c-which produces thesecond canary sound-is virtually iden-tical to the one formed by U1 -b, U2 -a,and U2 -b. The outputs of upper andlower halves of the circuit (at U2 -c and

R14 R19 -R17--I 1 I -R23-

R30 I c:8 I F44 I

R131 -R21-- C:4 R28 R1 R35+ 1 I I

R151C5 -R32-

R16-R31--- 1 EI

U2 1R27R29

-R20--R8- -R22--- R28 j R33 I

-R18- I R34 Ri2

912 ":" C9I

I c7

Ce

Fig. 3. Assemble the printed -circuit board using this parts -placement diagram as aguide. Take care to observe the proper orientation when installing the electrolyticcapacitors and the other polarized components.

SPKR1

J2 -b, respectively) are mixed via Iwo10k resistors (R1 and R2) and used todrive transistor Q1, which, in turn, drivesa miniature 8 -ohm speaker (SPKR1).

The 7th (and final) oscillator, builtaround U1 -a, is the control oscillatorand is used to turn the two sound -pro-ducing circuits on and off. Op -amp U1 -a initially has a low output for about 60seconds since the 100-µF capacitorhas to discharge from + 9 volts down to+ 2.3 volts. From then on, its output goeshigh for about 20 seconds, low for 20seconds, and so on. When the output ofU1 -a is low, the chirp -control oscillators(U1 -b and U1 -d) are enabled via diodesD1 and D2.

Construction. The Hot Canaries cir-cuit was built on a printed -circuit boardmeasuring 41/4 x 21/2 inches. A foil pat-tern for the printed -circuit board isshown in Fig. 2. Once you've etchedand drilled your board, and gatheredthe parts listed in the Parts List, con-struction can begin. Start by installing ICsockets at the locations indicated in theparts -placement diagram (Fig. 3). It is

suggested that you install the passivecomponents (resistors and capacitors)first, beginning with the resistors andthen the capacitors. Be sure to observethe proper orientation for the elec-trolytic capacitors.

Follow the passive components withthe semiconductors, beginning withthe two diodes; keep in mind that thoseunits must be properly orientated. Afterthat, install transistor Q1, but do notplace the IC's in their sockets at thispoint. Next install a 9 -volt, transistor -ra-dio -battery holder on the board whereindicated. Connect a 9 -volt batteryconnector to the board. Connect S1 tothe board through short lengths ofhook-up wire. Do the same for thespeaker. Now Icy the board to the sideand prepare the enclosure that willhouse the circuit.

The author chose to house the circuitin a plastic enclosure measuring about6 x 31/o x 11/2 inches. Prepare the en-closure by first marking the location ofthe speaker on the inside of the en-closure's lid using a permanent marker.Within that area, drill several holes in thelid to allow the sound to exit the en-closure. Also drill a hole in the lid awayfrom the speaker location for switch S1.Mount S1 and glue the speaker to theinside surface of the lid. Install the IC's in

(Continued on page 109) 31

TheElectromagneticRing ma

LauncherBY VINCENT VOLLONO

Explore the principles of electromagneticpropulsion with this simple ring launcher

Many methods,.such as gun-powder, spring action,water power, etc., have

been used to propel various objects.But has anyone given any thought topropelling objects by electromag-netic repulsion? The principle of elec-tromagnetic propulsion is a simpleone based on the fact that like -charged bodies tend to repel eachother; e.g., if a negatively (orpositively) charged body is broughtnear another negatively (or positively)charged body, they tend to pushagainst each other.

That principle (electromagnetic re-pulsion) is at the heart of theElectromatic Ring Launcher de-scribed in this article.

Circuit Description. Figure 1 is aschematic diagram of the Elec-tromagnetic Ring Launcher. Thelauncher circuit is comprised of foursub -circuits: a clock circuit, a count-down/display circuit, a trigger circuit,and a reset circuit.

The clock circuit is built around U5 (a555 oscillator/timer configured for as-table operation) and a few supportcomponents. The counter circuit isbuilt around U3 (a 74190 synchronousup/down counter with BCD outputsthat is configured for count -down op-eration), U4 (an ECG8368 seven -seg-ment latch/decoder/driver), and

DISP1 (a common -cathode seven -seg-ment display). The triggercircuit is comprised of U6 (anMOC3010 optoisolator/couplerwith a Triac-driver output), an SK3665Triac and a few support components.The reset circuit is composed of U1 (a7400 quad 2 -input NAND gate), U2 (asecond 555 oscillator/timer config-ured for monostable operation), anda few support components.

When power is first applied to thecircuit, the output of a flip-flop (com-prised of U1 -a and U1 -b) at U1 -b pin 6is low. That low is applied to pin 11 ofU3, disabling it so that the clock pulsesfrom U5 are ignored, and DISP1 dis-

WARNING!! This article deals with and in-volves subject matter and the use of materialsand substances that may be hazardous tohealth and life. Do not attempt to implement oruse the information contained herein unlessyou are experienced and skilled with respect tosuch subject matter, materials and sub-stances. Neither the publisher nor the authormake any representations as for the com-pleteness or the accuracy of the informationcontained herein and disclaim any liability fordamages or injuries, whether caused by orarising from the lack of completeness, inac-curacies of the information, misinterpretationsof the directions, misapplication of the infor-mation or otherwise.

plays a count of 9. When S1 is pressed,the output of the flip-flop goes high.That high enables U3, causing it tobegin its descending count, output-ting the count (in BCD form) to theseven -segment latch/decoder/driver,U4. The latch/decoder/driver de-codes the BCD data and activatesthe appropriate segments of DISP1 todisplay the descending count.

When the count on U3 reacheszero, pin 12 of U3 goes high. From U3,the high output divides along twopaths. In one path, that signal is fedthrough R5 (a 470 -ohm resistor) to pin1 of U6 (the optoisolator/coupler). Thatcauses U6's internal LED to turn on, ac-tivating its internal Triac driver. The Tri-ac driver, in turn, triggers TR1 (anSK3665 200-PIV 4 -amp Triac), sendinga burst of current through L1. The cur-rent going through L1 induces an op-posing current in the aluminum ring,causing the ring to be propelled intothe air.

At the same time, in the other path.the pin 12 output of U3 is fed to thebase of 01 through R4 (another 470 -ohm resistor), causing it to conduct.With 01 conducting, pin 2 of U2 ispulled low, triggering the monostable

timer. The output of the monostable atpin 3 goes high for about 11/2 seconds.That high is fed to pin 1 of U1 -a, caus-ing the flip-flop output at pin 6 to golow, once again disabling the counter,and resetting the display to 9. Potenti-ometer R8 is used control the clockfrequency which, in turn, controls thecounter rate.

The circuit is powered from a regu-lated 5 -volt power supply consistingof T1, BR1, U7, and C4. Transformer T1 (a12 -volt 2 -amp unit) reduces the 117 -volt AC line voltage to 12 -volts AC. Theoutput of the transformer is then ap-plied to BR1 (the fullwave-bridge rec-tifier), which provides a pulsating DCoutput. The output of the bridge rec-tifier is then filtered by capacitor C1,and fed to U7, which provides a regu-lated 5 -volt DC output.

+ 5V

R2100K

1Ak8

7

C214

PL1

117VAC

Construction. The author's pro-totype of the Electromagnetic RingLauncher was assembled on a singlesection of perfboard using point-to-point wiring. When assembling theproject, it is recommended that sock-ets be provided for all of the IC's, andthat Triac TR1 be mounted to a heatsink. It is further recommended that asocket be provided for the display;socketing the display allows you towire the socket to the display withoutrisking thermal damage to the unit it-self. Note that the display is notmounted to the circuit board alongwith the other components, but is in-stead mounted to the side of the en-closure (where it can be seen) alongwith S1 (the trigger or start switch).

Begin assembly by mounting thesockets for the IC's to the board; but

do not install the IC's in their socketsuntil the project is completely as-sembled and checked for cor-rectness. The sockets, in addition topreventing thermal destruction to theIC's, also allow easy parts substitutionshould that become necessary. Oncethe sockets are installed, wire the cir-cuittogether using Fig. 1 as a guide. Becareful when installing the polarizedcomponents (diodes, Triac, fuliwave-bridge rectifier, etc.). Installing one ormore of those components incor-rectly can, and probably will, result inan inoperative circuit and destroyedcomponents. In the worst -case sce-nario, incorrect wiring of the circuitcould also place you at greater shockhazard; remember, coil LI is fed di-rectly from the AC line, In short, a littlecare now can save a lot of aggrava-

R62.2Kw,

t R110K

U2 201555

C1

T.ot

T1

12V2A

R31K

L1*0 Ono-

MT1

TR1

SK3665

141/47400

U1 -a3

4

5 I U1 -b

7

S

6

915

11

1/4 7400

012N3904 R4

47011§

U6MOC3010

MT2

6

*SEE TEXT

5A50PIV

C4

4700

12

R547052

U77805

G

3-5 VOLT

SOURCE

10 8

U374190

3

7

2 6

2

7

6

U4EC68308

14 15 9 101

16

14

5

16

d

e

Fig. I. The Electromagnetic Ring Launcher is comprised of four sub -circuits: a clockcircuit (built around U5, a 555 oscillator/timer configured for astable operation), acount-down/display circuit (built around U3, a 74190 synchronous up/down counterwith BCD outputs that is configured for count -down operation; U4, an ECG8368BCD -to -seven -segment latch/decoder/display driver; and DISPI, a common -cathodeseven -segment display), a trigger circuit (comprised of U6, an MOC3010 optoisolatorlcoupler with Triac-driver output; TRI, an SK3665 200 -Ply, 4 -amp Triac; and a fewsupport components), and a reset circuit (composed of Ul , a 7400 quad 2 -input NANDgate; U2, a second 555 oscillator/timer configured for monostable operation; and afew support components).

R81MEG4is,

4

U5555

110.t R7

100K

DISP1

CC

CC

C310

PARTS LIST FOR THE ELECTROMAGNETIC RING LAUNCHER

SEMICONDUCTORS

U1-7400 quad 2 -input NAND gate.integrated circuit

U2, U5-555 oscillatoritimer,integrated circuit

U3-74190 synchronous up/downcounter with BCD outputs,integrated circuit

U4-ECG8368 BCD -to -7 -segmentlatch/decoder/display driver,integrated circuit

U6-MOC3010 optoisolator/couplerwith Triac driver output, integratedcircuit

U7-7805 5 -volt. I -amp voltageregulator, integrated circuit

Q1 -2N3904 general-purpose NPNsilicon transistor

TRI-SK3665 200 -Ply, 4 -amp Triac

DI -1N4001 50 -Ply, I -amp rectifierdiode

BRI-50-PIV, 5 -amp, fullwavebridge rectifier

DISP1-Common-cathode, 7 -segment LED display (see text)

RESISTORS(All fixed resistors are 1/4 -watt. 5%

units.)R1 -10,000 -ohmR2, R7 -100.000 -ohmR3-I000-ohmR4, R5 -470 -ohmsR6 -2200 -ohmR8-l-megohm, trimmer

potentiometer

CAPACITORSC1-0.01-p.F, ceramic -disc

C2 -14-µF, 10-WVDC, electrolytic10-WVDC, electrolytic

C4 4700-µE 35-WVDC,electrolytic


TI -12 -volt, 2 -amp powertransformer

PL1-117-volt molded AC power plugwith line cord

Pertboard materials, enclosure (seetext), aluminum ring (see text),#28 magnet wire, 3 -inch length of1/2 -inch diameter paper tubing, 1 -foot length of '/2 -inch diametersteel rod, heat -shrink tubing,heavy -gauge electrical wire, hook-up wire, electrical tape. solder,hardware, etc.

lion later.Coil LI is a hand -wound unit that

was made by winding 1/4 -pound of#28 magnet wire on a1 -inch diame-ter paper tube about 3 inches long,fitted onto a 1/2 -inch diameter 1 -footlength of steel rod that was first cov-ered with black heat -shrink tubing.

PRIMARY COIL

1/2 INCH IRON CORE

After winding the coil, heavy gaugeinsulated wire was connected to thecoil ends, and electrical tape waswrapped around the coil body tohold the windings in place.

The Electromagnetic Ring Launch-er was housed in a home-madewooden enclosure (which with its pro -

WOOD BLOCK

PLYWOOD BOX SWITCH

SEVEN SEGMENT DISPLAY

Fig. 2. When your project is completed, it should bare some remote resemblance tothis illustration, with its gun -turret like core support from which to launch the ring.The ring-which must be made of a non-magnetic metal-was cut from a length of 1/4 -

inch diameter aluminum tubing to 1/2 -inch in length.

truding metal rod resembles a bat-tleship gun turret, see Fig. 2), however,any non-metallic enclosure of suit-able size will do. The enclosure usedfor the author's prototype was madefrom 1/2 -inch plywood.

In any event, regardless of the typeof enclosure used, a cutout must bemade in the side of the enclosure forDISP1. Once the cutout was made, thedisplay was epoxied into place. You'llalso have to drill a hole in the en-closure for switch S1. When your proj-ect is completed, it should looksomething like the illustration in Fig. 2.

The ring was cut from a length of 3/4 -inch diameter aluminum tubing to'/2-inch in length. The ring must be madeof a non-magnetic metal such as alu-minum. If a magnetic metal is used, itwill be attracted to the core, nullifyingthe principle on which the project isbased.

Troubleshooting. While the circuit isso easy to build that it should work justfine the first time, construction errorsmay find their way into the circuit. Be-fore applying power to the circuit,thoroughly inspect the circuit boardfor construction errors-cold solderjoints, misconnected components,shorts, etc.-that may prevent the cir-cuit from operating. Caution: AC linevoltage Is used in transformerlessfashion in the trigger section of thecircuit to supply the necessary burstof AC current to 1.1, therefore, cau-tion must be exercised. Do not


If you are like manypeople, you probablyown a telephone -an-

swering machine so thatyou never miss an impor-tant phone message. Butwhat about those impor-tant messages at home orwork that don't come fromthe telephone? How oftendo you search for penciland paper just to leave afamily member or co-worker a short note? Orhow frequently, when driv-ing your automobile, doyou think of something im-portant that you need tobe reminded of later?Wouldn't it be great if youcould just press a button torecord your thoughts andinstantly recall them when-ever you desire?

You can do that andmore with the PersonalMessage Recorder, de-scribed in this article. Itworks like a conventionaltape recorder except thatit is completely solid state. Itfeatures instant playbackbecause there is nothing tore -wind. In addition, it willhold messages for morethan 10 years without anypower!

PERSONALMESSAGERECORDERThis state-of-the-art, solid-state recorderuses no tape and can store messages for

up to 10 years.How It Works. The projectis based on the new ana-log storage technology.Current techniques for recordinganalog signals involve several steps. Ingeneral, the signal is first compressed(or encoded) and then converted todigital values by an analog -to -digitalconverter. The converted values arestored in a large digital RAM area.That memory area requires a batteryto prevent data loss when power isremoved.

When the signal is to be playedback the digital data is clocked out ofthe RAM to a digital -to -analog con-verter. Finally, the restored signal pass-es through an expander (or decoder)circuit and an output amplifier, whichfeeds the signal to a speaker. That tra-ditional approach is very compli-cated. And even with sophisticatedcompression schemes, hugeamounts of memory are required to

BY DAVID WILLIAMS

store relatively small amounts ofspeech. Typically, a 32,000 -bit RAMholds less than 2 seconds of speech.

The Personal Message Recorder isbuilt around an ISD1016 CMOS voicemessaging system, which does awaywith the cumbersome and expensiveanalog -to -digital and digital -to -ana-log conversion circuits. The ISD1016made by Information Storage De-vices, Inc., of Austin, TX uses CMOSEEPROM technology to directly sam-ple, store, and playback analog sig-nals. And since EEPROM storage isnon-volatile, the ISD1016 holds its dataindefinitely without power.

A functional block diagram of theISD1016 is shown in Fig. 1. The ISD1016contains all of the functions necessaryfor a complete message -storage sys-tem. The pre -amplifier stage accepts

audio signals directly froman external microphoneand routes the signal to theAN.A our (analog out) termi-nal. An automatic -gaincontrol (AGC) dynamicallyadjusts the preamplifiergain to extend the inputsignal range. Together thepreamp and AGC circuitsprovide a maximum gainof 24 dB. The internal clocksamples the signal and, un-der the control of the ad-dress -decoding logic,writes the sampling to theanalog -storage array. Eightexternal input lines allowthe ISD1016's messagespace to be addressed in160 equal segments, eachwith a 100 -millisecond du-ration. When all addresslines are held low, the stor-age array can hold a sin-gle, continuous, 16 -secondmessage.

The ISD1016 also includescontrol signals for cascad-ing multiple chips in orderto achieve longer record-ing and playback times.Additionally, the ISD1016has an internal output am-plifier that can drive an ex-ternal speaker with up to50 mW of power.

Figure 2 shows the com-plete schematic of the Per-sonal Message Recorder.The circuit is very straight-

forward, since the ISD1016 takes careof most functions. However, there is aspecial addition to the POWER DOWNinput (pin 24) of U1. As mentioned ear-lier, the ISD1016 is designed to allowcascading multiple chips for longerrecording times. That's a useful fea-ture, but it causes a slight problem inour application. If the internal memo-ry becomes full during recording, anoverflow condition is generated inorder to trigger the next device. Oncean overflow occurs, pin 24 must betaken high and then low again beforea new playback or record operationcan be started.

A separate reset switch could beused to clear any overflows, but thatwould make the operation awkward.Instead, transistor Q1 along with com-ponents C3, R5, and R6 form a one-

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Fig. 1. This block diagram shows the internal structure of the 1SD1016 voice -messaging system integrated circuit.

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RFC/PLAYcr)a)'- Fig. 2. The Personal Message Recorder is comprised almost entirely of the 1SD1016,36 with a few additional components rounding out the system.

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shot pulse generator that automat-ically clears any overflow conditioneach time the START switch (S1) is

pressed. Switch S2 selects either theplayback or the record mode. SwitchS4-an 8 -position (a -h) DIP switch-is

SP+ included in the circuit to allow the cir-

SP-cuit's record/playback time to be var-ied from 0 to 16 seconds, themaximum time being available whenall 8 switch positions are close (or set

AUX IN to the on position). Resistor network R8(a -h) is included in the circuit to pro-vide a pull-up function for the addresslines, thereby controlling U1's record/playback time.

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Construction. Building the recorderis reasonably easy since the circuitcontains few parts. However, since theISD1016 has both analog and high -frequency digital signals within thesame package, several precautionsmust be taken to assure good voicequality. First the analog componentsshould be located close to U1, and allcomponents -lead lengths must bekept as short as possible.

Also note that the ISD1016 has sepa-rate digital and analog power andground pins. It is important to keep allfour paths separate when wiring thecircuit, and to tie the isolated powerand grounds together at only at the+V and ground sides of C1/C7 paral-lel combination, respectively. Lastly,the microphone ground must be tiedto analog ground (VssA) and never todigital ground (J).

The template of the circuit layout,shown half size in Fig. 3, incorporatesall of those guidelines and will fit nic-ely into a Unibox plastic enclosure. Be-gin construction by referring to theparts -placement diagram shown inFig. 4. Install the jumpers using 22 -gauge bus wire. Next mount all of theresistors and install a 28 -pin socket forU1. Then solder transistor Q1 and theSIP resistor network R8 (a -h), carefullyobserving the proper orientation ofeach. Install all of the capacitors andcheck the orientation of the polarizedelectrolylics.

The voltage regulator (U2) is

mounted vertically with the metal tabfacing away from U1. No heat sink isrequired in this application. Install the8 -position DIP switch (S4). The micro-phone (MIC1), switches (S1 -S3), andthe speaker (SPKR1) are mounted sep-arately from the circuit board and are

F3 .3 041,3

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Fig. 3. Here is a half-size template ofthe author's printed -circuit artwork,which incorporates all of the guidelines!restrictions outlined in the body of thearticle.

wired according to Fig 4. Use 26-28gauge hookup wire for the threeswitches and the speaker. Connectthe microphone to the board usingshielded wire only. Try to keep alllengths of wire between the boardand the off -board -mounted compo-nents as short as possible, while allow-ing enough for the parts to mount tothe cover of the enclosure withoutbeing pulled too taut. The wires of the9 -volt battery connector must bethreaded through the battery corn -

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Fig. 4. Assemble the Personal Message Recorder using this parts -placement diagramas a guide. Start with the jumpers, followed by the resistors and a 28 -pin socket forUI; then on to transistor Q1, the SIP resistor network R8, and the capacitors.

partrnent in the plastic case beforesoldering them to the circuit board.After attaching the battery con-nector. Mount the board in its case,

PARTS LIST FOR THE PERSONAL MESSAGE RECORDER

SEMICONDUCTORSU1 -1S1)1016 single -chip voice

messaging system, integratedcircuit (Information StorageDevices, Inc.)

U2-LM7805 5 -volt, 1 -amp, voltageregulator, integrated circuit

QI-2N4403 general-purpose PNPsilicon transistor

RESISTORS(All fixed resistors are VI -watt, 5%

units.)RI -1000 -ohmR2 -2200 -ohmR3 -10.000 -ohmR4, R5 -47,000 -ohmR6 -220,000 -ohmR7 -470,000 -ohmR8 -10.000 -ohm x 9 SIP resistor

network

CAPACITORSCI-C3 0.1-11F, ceramic -discC4 -1-µF, 16-WVDC, electrolytic

16-WVDC, electrolyticC6 -22-µF, 16-WVDC, electrolyticC7-220-uf, I6-WVDC, electrolytic

SWITCHESSI SPST momentary contact,

pushbutton switchS2_-SPOT toggle switchS3-SPST toggle switchS4 -8 -position DIP switch


MICI-Electret microphone elementSPKR1-8- or 16 -ohm speakerB1 -9 -volt transistor -radio batteryPrinted -circuit materials, Unibox

#188 plastic enclosure. 9 -voltbattery connector, shielded wiretsee text), hookup wire., solder,hardware, etc.

Note: The following items arcavailable from LNS Technologies,20993 Foothill Blvd., Suite 307,Hayward. CA 94541-1511: Tel.510-886-9296; A complete kit ofparts, including all components. aPC board, and plastic case, alongwith complete assemblyinstructions (order part #VMS -KIT) for $69.00; ISDI016 analogstorage system (UI) for $32.00.Add $3.00 for shipping andhanding to all orders. Californiaresidents please add appropriatesales tax.

and install U1 in its socket, making surethat the IC is properly oriented.

The Unibox case already hasmounting provisions for the speaker,but you will need to drill holes for themicrophone and switches S1 -S3.

Operation. Install a 9 -volt batteryand set all of the DIP switches to theiron positions. That sets the starting ad-dress to zero and gives you up to 16seconds of recording time. Flip S3 toON and switch S2 to RECORD. Hold downswitch S1, while speaking into the mi-crophone, and when finished releaseS1.

It is not necessary to shout or to getclose to the microphone while re-cording a message. The AGC circuitadjusts the gain of the preamp to pro-duce sufficient signal strength for therest of the circuit. Once a message isrecorded, it is stored indefinitely, untilchanged by the user, even when thepower is turned off, Subsequent press-ing of the sTART switch (S1) while speak-ing into the microphone will automat-ically record over the previousrecorded message.

To playback a message, flip S2 tothe PLAYBACK position and momentarilypress S1 (stAor). It is not necessary tohold S1 down during playback. In fact,pressing START during playback imme-diately re -starts the message from thebeginning.

We are surrounded byenergy that we can-not detect using our

senses. For instance, the elec-tromagnetic signals that comealive through the magic of ra-dio have been passing throughyou and your home completelyunnoticed. You are not aware ofthe electromagnetic radiationbecause the human body lacksthe capacity to detect thosesignals; you can't see, hear, feel,or taste electromagnetic radia-tion (unless it is in the visible -lightportion of the spectrum). Thesame is true of many otherforms of radioactivity.

Most people are concernedwith radioactivity and ionizingradiation due to its relationshipto atomic weapons and nu-clear power plants. When a nu-clear power plant has anaccident-such as the onesthat occurred at Three Mile Is-land and Chernobyl-the me-dia and a few anti-nucleargroups go into a feeding frenzy.That pushes public fears to thepoint where nuclear powerplants are forced to shut downbefore they have started pro-ducing power. That fear helpedprevent the opening of LILCO'sShoreham nuclear power sta-tion on Long Island, New York.

That fear, while well founded,overlooks the medical, scien-tific, and economic benefitsthat nuclear technology has of-fered humanity. No one is ad-vocating that anyone treatatomic radiation or nuclearmaterials lightly-you should not-butit is not a technological monster ei-ther, considering that life on this plan-et has evolved in a naturally -occurring, radiation -rich environ-ment. Yes, radiation permeates ourvery being. For example, radioactivematerial can be found in food we eat(potassium -40 and carbon-14) and inthe soil (uranium -238 and thor-ium -232).

Radioactivity. What is radioactivity?Radioactivity (a term coined by Pierreand Marie Curie) is defined as thespontaneous emission of energy and/or particles from the atomic nucleusof certain elements. The energy emit -

GeigerCounterThis project can be used to

detect and identify radiationsources in and around your home

BY JOHN !OVINE

ted can take the form of electromag-netic energy (called gamma rays),while the particles are typically alphaand beta particles.

Alpha particles are helium -4 nu -deli, consisting of two protons andtwo neutrons. When an atomic nu-cleus emits an alpha particle, itchanges into another nuclide with anatomic number of two units less and amass number of four units less.

Beta particles, which can be eitherelectrons or positrons (positive elec-trons), are more penetrating than al-pha particles. But they can bestopped by thin sheets of metal (suchas aluminum) or a few feet of air.

Gamma rays are typically deep -

penetrating emissions; i.e., theycan go through several inchesof metal. Gamma rays are pho-tons of energy (quanta) emit-ted from excited atoms. Whenan atom (such as Uranium 238)emits an alpha particle, it be-comes Thorium -234. The Thor-ium atom at this point hasexcess energy. it is said to be inan excited state. But by emittinga gamma ray, it drops to itsground (unexcited) state.

Measuring Radiation. Radia-tion is measured in curies, aquantity described as theamount of radiation given offby one gram of radium; aquantity that's equal to37,000,000,000 (3.7 x 1010)

atomic breakdowns per sec-ond. Because the curie is arather large number, many ra-dioactive sources are mea-sured in millicuries or microc-uries.

In order to detect radioac-tivity, you need an instrumentspecifically designed to detectsuch energy. There are anumber of ways to measure ra-dioactivity; scintillation, PN junc-tions, autoradiography, andgas -ionization. The Geiger -Muller (GM) tube, which workson the gas -ionization principal,can detect alpha, beta, andgamma radiation. If you areconcerned about possible ex-posure to radiation, then per-haps the Geiger Counter de-scribed in this article can helpto put your mind at rest.

Our Geiger Counter, which is basedon the gas -ionization method of de-tection, will give visual and audibleindications of local radioactivity. itcan be used to detect nuclear radia-tion or contamination in and aroundyour home, to prospect for uranium,and measure background radiation.In fact, it can even be used to detectlarge solar flares.

Figure 1A shows the basic operatingprincipal of the GM tube. The tubeconsists of a cylindrical electrode(cathode) surrounding a center elec-trode (anode). The tube is evacuatedand filled with a neon- and halogen -gas mixture. A voltage of 500 volts isapplied across the tube through a 10-

GM TUBE

RADIATION CATHODE

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GM TUBE VOLTAGELN-712

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Fig. 1. The Geiger -Muller tube consistsof a cylindrical electrode (cathode)surrounding a center electrode (anode).The tube is evacuated and filled with aneon- and halogen -gas mixture.

megohm, current -limiting resistor, R1.The tube has an extremely high resis-tance when it's not detecting radi-oactivity. When an atom of the gas isionized by the passage of radiation,the free electron and positivelyionized atom created move rapidlytowards the anode and cathode ofthe GM tube, respectively. In doing so,they collide with and ionize other gasatoms, thereby creating a small ava-lanche effect.

The ionization causes the resistanceof the tube to drop, passing a suddensurge of current that creates a volt-age pulse across R2. The halogen gasquickly quenches the ionization, re-turning the GM tube to its high initialresistance and enabling it to detectanother particle.

The number of pulses -per -minutethat the GM tube generates rises withthe voltage across its electrodes. (Fig.1B). By increasing the voltage, aplateau is reached where the pulserate stays pretty constant. The plateaurange for the GM tube used in ourGeiger Counter is between 400 and

600 volts with a recommended oper-ating voltage of 500 volts. If too muchvoltage is applied to the tube, whenthe tube detects a radioactive parti-cle the avalanche created will not bequenched, putting the tube in a stateof continuous discharge that candamage it.

A Look at the Circuit. Figure 2 is aschematic diagram of the GeigerCounter. The circuit is built around a4049 hex inverter (U1), a pair of 555oscillator/timers (U2 and U3), two tran-sistors, a Geiger -Muller tube, and afew additional support components.The first 555 (U2) is configured for asta-ble operation. The output of U2 (a se-ries of negative -going pulses) at pin 3is fed to three parallel -connected in-verters (U1 -a, U1 -b, and U1 -c). Thepositive -going output pulses of the in-verters are fed to the gate of Q1, caus-ing it to toggle on and off in cadencewith the applied signal.

The output of Q1, which is con-nected in series with the primary ofstep-up transformer T1, produces astepped -up series of pulses in T1's sec-ondary. The output of T1 (approxi-mately 300 volts) is fed through avoltage doubler (consisting of D1, D2,C3, and C4), producing a voltage ofaround 600 volts. Three series -con-nected Zener diodes (D3, D4, and D5)are placed across the output of thevoltage doubler to regulate the out-put to 500 volts. That voltage is fedthrough R4 (a 10-megohm current -limiting resistor) and J2 to the anodeof the GM tube. The limiting resistoralso allows the detection ionization tobe quenched.

The cathode side of the tube is con-nected to ground through a 100k re-sistor, R5. When a particle is detectedby the GM tube, the gases within thetube ionize, producing a pulse acrossR5. That pulse is also fed through C5and applied to the base of Q2 (a

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Fig. 2. The Geiger Counter is built around a 4049 hex inverter (U1), a pair of 555oscillator/timers (U2 and U3), two transistors, a Geiger -Muller tube, and a fewadditional support components.

TIP120 NPN transistor), where it is am-plified and clamped to 9 volts. Theoutput of Q2 is inverted by gate U1 -d,and then used to trigger U3 (the sec-ond 555, which is configured formonostable operation). The output ofU3 at pin 3 causes LED1 to flash, andproduces a click that can be heardthrough speaker SPKR1 or head-phones.

The circuit is powered by a 9 -voltalkaline battery and draws about 28mA when not detecting radiation.

Construction. There is nothing crit-ical about the circuit. In fact, if you aremore comfortable with point-to-pointwiring, there is no compelling argu-ment against you going that route.The author's prototype of the GeigerCounter, however, was assembled ona printed -circuit board. A full-size tem-plate of the foil pattern is shown clear-ly in Fig. 3.

Once you've etched your printed -circuit board and gathered the parts,construction can begin. It is recom-mended that all of the IC's be sock-eted. Start by first installing IC socketswhere indicated in Fig. 4. Then installthe jumper connections, followed bythe on -board components. After that,solder lengths of wire to the board forconnection to the off -board compo-nents. When that is done, check yourwork for errors. Once you are satisfiedthat the circuit contains no errors,place the board to one side and pre-pare the project's enclosure.

J2

J1

LED1 SPKR1

Fig. 4. Begin assembling the project by first installing the IC sockets where indicated,followed by the jumper connections, and then the on -board components. After that,connect lengths of wire to the board for connection to the off -board components.

Any plastic enclosure large enoughto hold the circuit board and othercomponents can be used to housethe project. Prepare the enclosure bydrilling holes for J1 and J2, LED1, andS1. Jack J1 is an enclosed, closed-cir-cuit type selected to mate with aheadphone plug. Jack J2 is a 1/8 -inchopen -frame, closed-circuit type. Thecenter contact of J2 should be con-nected to R4 and the outer contactconnects to R5. It will also be neces-sary to make an opening in the en-closure for the speaker, SPKR1. Mountall of the off -board components tothe enclosure, and connect the cir-

ea INCHES

Fig. 3. The author's prototype was assembled on a printed -circuit board. A full-sizetemplate of the foil pattern is shown here.

cuit-board wires to the appropriatecomponents. Once that's done,place that assembly to one side andprepare a housing for the Geiger -Muller tube.

Although the circuit is designedaround the LN-712 Geiger -Mullertube, it is possible to use other Geigertubes by altering the power -supplyoutput accordingly. The power supplyused in our circuit can be used topower any tube requiring up to 700volts by eliminating or substituting aZener diode of the proper rating. Forinstance, if you have a tube that re-quires a 300 -volt source, simply re-move one of the 200 -volt Zenerdiodes and replace it with a jumperwire. Or if the tube requires a 600 -voltsource, remove the 100 -volt Zener di-ode and replace it with another 200 -volt unit. In addition, using anothertube may require that the value of thecurrent -limiting resistor (R4 in the sche-matic diagram) be scaled accord-ingly.

The GM tube is delicate and shouldbe handled carefully. The GM tubehas a thin mica window on the frontend that allows alpha and beta parti-cles to penetrate and be detected.That window is easy to break, render-ing the tube useless. The authorhoused the GM tube in a plastic cointube. The coin tube was prepared bydrilling several tiny holes in the lid.Those holes allow alpha and betaparticles to get to the mica windowunimpeded.

In the bottom of the coin tube, theauthor drilled a hole just largeenough to pass the end of a 3 -footlength of two -conductor shielded ca-ble through. The conductors within thecable are color coded, greatly sim-plifying the proper wiring of the GMtube. One end of the shielded cablewas then connected to the GM tubeand the other end to a 1/8 -inch plugthat connects the GM tube to the cir-cuit board through J2.

Connect one conductor of the ca-ble to the anode (center lead) of theGM tube, and connect the other endof the same conductor to the centercontact of the plug. Connect theother conductor to the cathode (out-er lead) of the Geiger -Muller tube,and the other end of that conductorto the outer contact of the plug, sothat the cathode is tied to ground(through R5) when the GM tube isplugged in.

The GM tube was cushioned on thesides and bottom using soft non-con-ductive foam rubber. Note: If con-ductive foam is used, do not allow the

foam to touch the electrodes of theGM tube. That will put a short acrossthe GM tube, rendering the unit in-operative. A small amount of velcrowas then used to secure the GM hous-ing to the case.

Checkout and Troubleshooting.Before plugging in the GM tube, it's agood idea to see if the circuit is func-tioning properly. Turn on the circuitand measure the voltage from the D3/C3 junction to ground; it should beapproximately 500 volts DC.

If the voltage is too low, or you getnone at all, check the primary side ofT1; There should be a pulsating DCsignal across the primary of the trans-former. Also check the orientation ofthe Zener diodes. Continue back-tracking in that manner, checking thebase of Q1. You should be getting a 5 -kHz squarewave signal. Check pin 3 ofU2 using a scope.

Once the circuit is working, power itdown and plug in the GM tube. Thenturn it on again, and note whether itbegins to click. The author gets a

PARTS LIST FOR THE GEIGER COUNTER

SEMICONDUCTORSU1-4049 hex inverting -buffer,

integrated circuitU2, U3-555 oscillator/timer,

integrated circuitQ1 -112F511 N -channel enhancement

MOSFETQ2-TIP120 silicon NPN transistorDI, D2 -1N4007 general-purpose

silicon rectifier diodeD3, D4-1N5388B 200 -volt Zener

diodeD5-IN527IB 100 -volt Zener diodeLEDI-Light-emitting diode (red)

RESISTORS(All resistors are 14 -watt, 5% units.)R1 -22,000 -ohmR2 -1000 -ohmR3 -10 -ohmR4-10-megohmR5, R7 -100,000 -ohmR6 -10,000 -ohm

CAPACITORSCl, C2-.01-ILF, polyesterC3, C4-.01411, 2000-WVDC,

ceramic -discC5 -1-11.F. 16-WVDC, electrolyticC6-.047-p.F, polyesterC7, C8-220-1J.,F, electrolytic


SPKR1-8-ohm speakerT1 -6 -volt to 330 -volt, step-up

transformerB1 -9 -volt alkaline batterySI-SPST toggle switchJ1, 12-see textPrinted -circuit materials. LN-712

Geiger -Muller tube (see text),enclosure, battery clip, etc.

Note: The following items for theGeiger Counter are available fromthe following vendors: The step-uptransformer (T1), part # C -2B, isavailable from Allegro Electronics(3 Mine Mountain Road, CornwallBridge. CT 06754: Tel.203-672-01231 for $3.99, plus$2.00 shipping and handling.Connecticut residents, please addappropriate sales tax.

The LN-712 Geiger -Muller tube isavailable from Images Company(P.O. Box 140742, Staten Island,NY 10314-0024, Tel.718-698-8305) for $48.00, plus$3.00 shipping and handling. NewYork State residents, please addapplicable sales tax.

reading of approximately 11 pulsesper minute from background radia-tion. As each particle is detected, thespeaker will click and the LED will flash.If you have acquired some radioac-tive material (we'll present somesources shortly) bring the GM tubeclose to it to test for activity.

Radioactive Sources. An easysource of a radioactive material-approximately one microcurie ofAmericium 241-can be found in aionization -type smoke detector.Americium is a strong alpha -particlesource. To use the Americium as asource, it must be removed from thesmoke detector. The alpha particlesonly travel an inch or so through theair so you'll have to get pretty closewith the GM tube to detect anything.

To get to the radioactive source, firstremove the plastic top of the smokedetector. The Americium is inside asmall ventilated metal can. Removethe can with pliers. The Americium isembedded in a metal plate under-neath the can. Remove the entireplate with the Americium from the de-tector. Leave the radioactive materialattached to the plate, and use thematerial on the plate. Bringing theGM tube within 1/2 -inch of the source,the reaction of the Geiger Counterwill become furious.

A more reliable source of radioac-tive materials is the Nucleous Compa-ny (601 Oak Ridge Turnpike, OakRidge, TN 37830; Tel. 615-483-8405 or800-255-1978). The company sellscalibrated and uncalibrated radio-active materials for students, schools,and industry. (I purchased a Ce-sium -137 gamma -ray source for$25.00. The material is rated at 5 mi-crocuries with a 30 -year half life. It wasenlightening when I placed a 3/4 -inchsolid block of aluminum in front of theCesium -137, and found there was nonoticeable decrease in radiation.)

"CZ

"Do you like our new motivational sign?"

An Enfor

PhotographicPrinting

BY RUDOLF F. GRAF ANDWILLIAM SHEETS

Get perfect photographic printsevery time with this easy -to -assemble darkroom accessory.

Using an enlarger light meterin the darkroom makes pro-ducing prints (both mono-

chrome and color) easier. It also savestime, trouble, and money in otherwisewasted materials. While there are anumber of such meters on the market,electronics enthusiasts who also dab-ble in photography can build a sim-ple meter to do the job at very littlecost. In this article we'll describe howyou can build the Enlarger LightMeter, at a cost of $25 or less depend-ing on how well stocked your spare -parts bin is.

The light meter (whicn is essentiallya comparator circuit designed spe-cifically for photographic work) is notcalibrated against any special stan-dard. That makes it easy to build, setup, and use. All it does is compare theincident light striking a light -depen-dent resistor (LDR) with a level that hasformerly been established-via a po-tentiometer and a rotary switch-ascorrect based on previous experi-ence.

Circuit Description. A schematic di-agram for the Enlarger Light Meter isshown in Fig. 1. Meter M1, a +/-50zero center D'Arsonval meter move-ment is driven by U1, a TL081 FET op -amp, through R3. The gain of U1 is setat 11 by R1 and R2, while capacitor C1

is used to restrict the bandwidth of U1to 1.6 Hz. Power for the circuit is derivedfrom a simple dual -polarity 12 -voltpower supply (consisting of T1, D3, D4,C2, and C3).

A light -dependent resistor (LDR), R16(which is a semiconductor elementwhose resistance decreases as it is ex-posed to increasing illumination), isused as a light -sensing device. Oneend of R16 is connected to the nega-tive supply rail through R12, while theother end is connected to pin 3 of U1,applying a negative current to U1. Avariable (over a 4:1 range) positivecurrent determined by the settings ofR14 and S1 (and derived from thepositive supply rail) is also fed to pin 3of U1.

When the two currents (of oppositepolarities) are equal, they canceleach other out, so effectively no cur-rent is applied to pin 3 of U1. With nocurrent applied to pin 3, the output ofU1 is zero, and meter M1 registers ac-cordingly, indicating a null. However,when light striking R16 causes its resis-tance to decrease, the currentthrough the device increases, makingthe negative current greater than thepositive current. Under that condition,the negative current causes the out-put of U1 to swing negative, causingthe meter's pointer to swing in thenegative direction.

That indicates that the light intensitymust be reduced by using a smallerlens opening on the enlarger (smallerf/stop). The opposite occurs if the lightis too dim. Lamp 11, a 12 -volt 60-mA"grain of wheat" unit, is used to illumi-nate the meter scale, while R15 is usedto limit I1's illumination to a faint glowthat is just bright enough so that theface of M1 can be plainly seen in aphoto darkroom.

Resistors R3 and R4 should be se-lected for the meter used. With a dualsupply of + /-12 volts, U1 produces anoutput voltage of 10 volts peak -to -

peak. The resistance of R3 can befound by dividing the peak voltage(i.e., 10/2) by the full-scale meter cur-rent (in amps); i.e., R3 = (10/2)/0.00005= 100,000 ohms. Resistor R4, the shuntresistor, should be selected to have avalue equal to the meter's internal re-sistance-in our case, 220 ohms.

Building the Circuit. There is

nothing critical about the con-struction of the Enlarger Light Meter.Most of the circuit was assembled ona couple of terminal strips, usingpoint-to-point wiring techniques. Wirethe circuit together using Fig. 1 as aguide. Note that R16 (the LDR), S1, R14,and M1 are not mounted with theother circuit elements. The LDR (whichwe'll get to a bit later) will be mounted

in its own enclosure and connectedto the other circuit componentsthrough a length of twisted -pair wire.Meter M1, switch S1, and resistor R14are all mounted at some convenientpoint on the circuit's enclosure. Notethat the schematic diagram shows S1as a seven -position switch; if a seven -position unit can not be located, a 12 -position unit (with five positions leftblank) will work just as well. Resistors R5through R11 can be connected di-rectly to S1's terminals and their freeends tied together, and then broughtout to the appropriate point in thecircuit.

Be careful when connecting thepolarized components. Connectingthem backwards could render the cir-cuit inoperative at best, or in the worst -case scenario, destroy one or twocomponents. Lamp M should be posi-tioned somewhere behind the meterscale, and if possible, painted orangeor red to reduce blue -light compo-nents emitted by the device; photopaper is sensitive to those light wave-lengths. Transformer T1 is not critical;the only requirement is that the trans-former be a 12 -volt unit that is able tosupply sufficient current to operatethe circuit. The enclosure used tohouse this part of the circuit can be ofany type that you choose.

As for the light -dependent resistor,R16, it should be mounted in separatehousing; a plastic bottle cap with ahole drilled in its center is suitable. SeeFig. 2. Begin by drilling a hole in thecenter of the bottle cap (or similarhousing). Mount the LDR so that its lensis centered over the opening. Epoxythe LDR in place, clip off the excessleads so that they do not extendbeyond the enclosure, and connect atwo -foot length of twisted -pair wire tothe LDR's leads. Attach a cover to therear of the sensor enclosure and com-plete the project by connecting thetwisted -pair wires from the sensor tothe appropriate points in the circuit asshown in the schematic.

Checkout. Once the circuit is fullyassembled, check for the usual con-struction errors; shorts, cold -solderjoints, wiring mistakes, etc. If all looksokay, apply power to the circuit. Thencheck for + 12 volts at the junction ofC2 and D3 (a voltage between+ 10-+ 15 volts is okay) and for -12volts ( - 10 to - 15 volts) at the junction

VNR1

100K

D1

1N914B

14

D21N914B

R1212012

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R21MEGAAA .

2

R6 R51.2K 33011AM

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220K 820K

I MIN

SENSITIVITYRANGE 4 R14

1

S1K

AMAXNULL

c R13

C2220

D4 -1N4007

117VAC

Fig. 1. As revealed by this schematic diagram, the Enlarger Light Meter is nothingmore than a comparator, built around a TL081 op -amp.

1/8" HOLELDR

,

mii111111!

EPDXY TO HOLD LDR IN PLACE

EPDXY

LIGHTENTERS HERE

N.rSOLDER

BOTTLE CAP -HOUSING

DRILL HOLE TO PASS WIRES

PLASTIC DISCCEMENTED IN PLACE

A

2' CORD

SNUG FIT

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AND D1/D2

1111111111111111111100 ME.t.

B

Fig. 2. The sensor (light -dependent resistor or LDR), R16, is housed in its ownenclosure, and connected to the rest of the circuit via a two -foot length of twisted -pairwire. Shown here are the details for that assembly's preparation.

of C3 and D4. Next, with R16 shieldedfrom light, set S1 to its maximum -sen-sitivity position. It should be possible tonull, or a least move, the pointer of M1by varying R14. Next, expose R16 to adim light (a 7 -watt night light about 3 -feet away). Adjust S1 and vary R14. You

should find a setting of S1 and R14where the meter nulls. If not, checkyour wiring.

Grounding pin 3 of U1 should nullM1. That verifies that U1, the powersupply, and M1 are operating prop-erly. If that test works, but you cannot 43

PARTS LIST FOR THE ENLARGER LIGHT METER

SEMICONDUCTORS1_11-T1_081. NTE857M (or

equivalent) WET -input op -amp,integrated circuit

1)1, 1)2-----IN91413 or equivalent,general-purpose silicon diode

1)3, D4--IN4007. or equivalent l-amp. 1000-PIV general-purposesilicon rectifier diode

RESISTORS(All fixed resistors are 1/4 -watt, 5c;

units.)R I , R3 -100.000 -ohmR2-1-megohmR4 -220 -ohmR5, RI3-330-ohmR6 -1200 -ohmR7--4700-ohmR 8 -18,0(M -ohmR9 -68.0(X) -ohmR10 -220.000 -ohmRI I -820,(88) -ohmR I2 -120 -ohm

R14 -1000 -ohm panel -mountedlinear -taper potentiometer

R15 -150 -ohm, I/2 -wattR16-Light-dependent resistor (see

text)

CAPACITORSC1 -0.1-µF, Mylar or ceramic -discC2. C3-220-p.F. I6-WVDC,

electrolytic


T1 -12 -volt 3(X)-mA or more, powertransformer

Ml-+; -50-µA zero centerD'Arsonval meter

SI-SP7T rotary switch (see text)11 -12 -volt 60-mA "grain of wheat"

lampTerminal strip ( see text), enclosure,

AC molded power plug with linecord, bottle cap, wire, solder,hardware, etc.

All of the electronics for the Enlarger Light Meter. except for the LDR were housedin a small enclosure on whose front panel switch SI, potentiometer R14, and meter MIare mounted. The LDR was housed in a separate enclosure about the size of a bottlecap, and connected to the circuit by wire leads.

get the meter to null, check R16, itswiring, and the wiring of R14, R13, S1,and R5 through R12.

Use. Do not expose R16 to very brightlight before attempting to use thelight meter. Bright light reduces the re-

sistance of R16, and it will take severalminutes for it to recover, therebythrowing off your readings for the firstfew minutes.

Begin by first making a good print(monochrome or color) using yourconventional technique, and record

the enlarger settings (distance be-tween lens and paper, f/stop, and ex-posure time). Next, place the negativeused for the print in the enlarger, andduplicate the recorded settings.Place R16 on a part of the image thatcorresponds to a medium gray tone.

Use meter -range switch S1 tocoarse null the meter (pointer at zerocenter). Then, use R14 to exactly nullthe meter. Note the meter settingsand leave it that way. That calibratesthe meter for your paper and printdeveloping technique.

When you to make another print,simply insert the negative in the en-larger. Compose and sharply focusthe picture, using the enlarger lens atmaximum aperture, usually f/3.5 orlarger. Place the light sensor in a partof the image that is to be a mediumgray in the final print, preferably anarea somewhere in the centralportion of the picture. Try to avoid thecorners or extreme edges if you can.

Now, without adjusting the lightmeter settings from those obtainedfrom the first negative, adjust the en-larger lens aperture for a null on themeter. That will be the correct ex-posure setting. Use the same ex-posure time and developing methodas you used for the first negative. Inserta sheet of photographic paper intothe enlarger easel, and make the ex-posure. Develop the print. It should becorrectly exposed.

You may also use a lighter gray toneor even total black as a referencepoint. The trick is to be consistent. Amedium gray reference point wassuggested because it seems to be theeasiest to judge. Others prefer thedarkest area (lightest gray or white onfinal print), which works equally well. Itis simply a matter of preference.

While the meter is primarily intend-ed for B/W printing, it may be alsoused for color, although it will give onlythe correct exposure; color balance isnot measured. However, if you havepredetermined the filter pack, themeter will work well for color. Use anarea of the negative that is neutral ornear neutral in color. In our experi-ence, flesh tones work well. For land-scapes, you can get good results ifyou use the sky areas as a reference.

That's all there is to it. Once this proj-ect is complete and operating, youshould be able to obtain near perfectprints every time.

Here is a chance for you toadd an accurate, but inexpe-nsive, digital frequency counterto your electronics arsenal

Portable 2 -MHzFrequency CounterBY ANTHONY J. CARISTI

Frequency counters have beenavailable to electronics engi-neers and technicians for many

years. But for the electronics hobbyist,particularly the newcomer, the cost ofsuch frequency -measuring instru-ments-usually upwards of $100 for abasic unit-can be prohibitive. For-tunately, even those on a meagerbudget can afford the Portable Fre-quency Counter. The counter is aneasy -to -build, basic (no -frills) unit thatcan measure frequencies up to 2 MHzwith a resolution of 1 Hz. That makes it ahandy instrument for audio, ultrasonic,and low radio -frequency applica-tions.

About the Circuit. Figure 1 shows afunctional block diagram of the fre-quency counter. The counter is madeup of several subassemblies: a crystaloscillator, a pair of divide -by -10 coun-ters, a 16 -stage binary counter, a trig-ger circuit, a latching circuit (RS flip-flop), an analog amplifier, a counter/display -driver circuit, and, of course,an LCD readout.

The crystal oscillator, which pro-vides a timing reference, generates ahigh -frequency signal that is twice di-vided by ten to provide three selecta-ble frequencies. The selected fre-quency is fed to the 16 -stage binarycounter (which further divides the se-lected frequency by 216). The output

of that binary counter is fed to thelatching circuit as a stop (or reset) sig-nal.

A low -frequency trigger oscillatorperiodically generates a start (or set)signal, which is also fed to the latch.The latch, in turn, outputs a pulse ofknown width (called a gate), which isfed to the counter/display driver andis used to initiate the measurement.

The input to the circuit (a signal ofunknown frequency) is fed to an ana-log amplifier, which boosts the signalsufficiently to operate the input to thecounter/display driver. The counter/display driver counts the number ofpulses applied to its input during thetime that the gate is active. The totalnumber of pulses is then decodedand used to light the appropriate seg-ments of a large 31/2 -digit LCD read-out.

A Closer Look. Figure 2 is a com-plete schematic diagram of the fre-quency counter. The crystal oscillator,comprised of NOR gate U3 -c and itsassociated components, is biased lin-early by resistor R5, while crystal XTAL1(connected from U3-c's input to itsoutput), causes U3 -c to oscillate at thecrystal's series -resonant frequency.The output of U3 -c is buffered by U3 -dand divided along two paths. In onepath, the signal is delivered to oneterminal of S2 -b (half of a double -

pole, three -throw switch); in the otherpath, the signal is fed to U6 -a (1/2 of aCD4518 dual synchronous up coun-ter), which is configured for divide -by -10 operation.

The output U6 -a is also dividedalong two paths, with one path goingto a second terminal of S2 -b, and theother going to U6 -b (also configuredfor divide -by -10 operation). Together,the two halves of the synchronouscounter provide a total frequency di-vision of 100. The output of U6 -b is fedto a third terminal of S2 -b, providingthree selectable frequency ranges.Those selectable frequencies deter-mine the gate time of the counter (10,100, or 1000 milliseconds). The se-lected frequency is fed to U4, the firstof two CD4040B ripple -carry binarycounters. The output of U4 is fed to U5(the second CD4040B ripple -carrybinary counter). Together U4 and U5provide a frequency division of 216, or65,536.

The output of U5 is fed to pin 6 of U3 -b, which with U3 -a forms a bistablemultivibrator (RS flip-flop), that is usedto control the start/stop sequence ofthe counter. The RS flip-flop is reset bythe output of U5 and set by the outputof U1, a CMOS 555 oscillator/timer thatis configured for low -frequency, asta-ble operation. The set and reset inputsof the flip-flop are labeled "start" and"stop," respectively.

XTAL

OSCILLATOR

TRIGGEROSCILLATOR

START

DIVIDE -BY -10

STOP

LATCH

DIVIDE -BY -10

GATE

ANALOGAMPLIFIER

Ct-RANGE

16 -STAGE

BINARY DIVIDER

1888E1

COUNTER

Fig. 1. The frequency counter is made up of several subassemblies: a crystal oscillatora pair of divide -by -10 counters, a 16 -stage binary counter, a trigger circuit, a latchingcircuit (RS flip-flop), an analog amplifier, a counter/display driver circuit, and, ofcourse, an LCD readout.

The negative -going output of U1,which is used to initiate the count se-quence to periodically update thefrequency display, is inverted by U2 -dbefore application to U3 -a. (The inver-sion is accomplished by tying one in-put to U2 -d high, and applying a lowto the other pin. That forces the outputof U2 -d to go high, each time a U1outputs a low.) The resulting positive -going pulse drives the output of U3 -aat pin 3 low. That low, which is appliedto pin 11 of both U4 and U5, causes U4and U5 to begin the count sequence.The output of U3 -a remains in a lowstate until the flip-flop is reset at theend of the count (65,535).

At the end of the count, pin 5 of U5goes high. That high is applied to pin 6of U3 -b, forcing its output high, whichdivides along two paths. In one path,the signal is fed to pin 2 of U3 -a, forc-ing its output high. That inhibits U4 andU5, resetting them to zero to await thenext trigger pulse. In the other path,the signal (a positive -going pulse of

o precise width -10,100, or 1000 millise-co° conds, depending on the selectedz clock frequency) is fed to pin 31 of U8z as a gate -control signal.a") Switch S2 -a (the second half of the

DP3P switch) is used to set the decimal>-co point for the higher frequency rangeso (200 kHz and 2 MHz). Decimal -point0) activation is accomplished through52 two xoR gates (half of a CD4030Bo quad 2 -input xoR gate, U2 -a and U2 -

b), which are used as conditional in -w verters. (An xoR gate produces a logicw 1 output only when the logic levels at iscp Iwo inputs are different from eachother.) Depending upon the setting of46 S2 -a, the selected unit inverts the

no decimal point since the 41/2 -digitreadout will display frequency directlyin hertz. When the counter is set to the20 kHz range, S2 -a activates field-effect transistor (FET) 01. Activating 01places C3 in parallel with C4, therebylowering the operating frequency ofU1 to about 0.5 Hz to accommodatethe 1 -second gate time that is re-quired for the 20 -kHz range.

The input frequency is fed throughJ1 to an analog amplifier, built around02 and 03. Transistor Q2 (a FET thatprovides a high input impedance tothe signal source) is used to drive 03(which is configured as a common -source amplifier). The total gain pro-vided by 02 and 03 is sufficient to

PARTS LIST FOR THEPORTABLE FREQUENCY

COUNTER

SEMICONDUCTORSUI-LMC555CN CMOS oscillator/

timer, integrated circuitU2-CD4030B quad 2 -input XOR

gate, integrated circuitU3--CD4001B quad 2 -input NOR

gate, integrated circuitU4, U5-CD4040B 12 -stage ripple -

carry binary counter, integratedcircuit

U6-CD4518B dual decade counter/divider, integrated circuit

U7-AN78L05 5 -volt, 100-mA,voltage regulator, integrated circuit

U8-ICM72241PL counter/display-driver, integrated circuit

Ql-BS170 N -channel enhancementMOSFET

Q2-MPF102 (or SK9164) N -channelJFET

Q3 -2N3906 general-purpose PNPsilicon transistor

DISPI-41/2-digit LCD readout (Digi-Key LCD -004 or equivalent)

RESISTORS(All fixed resistors are 14 -watt. 5%

units.)RI. R2 -220,000 -ohmR3 -100.000 -ohmR4 -470,000 -ohmR5-10-megohmR6, R8-1-megohmR7-I0,000-ohmR9, R10 -1000 -ohm

R11 -470 -ohmR12 -4700 -ohmR13-47 .000 -ohm

CAPACITORSCI, C2. C5, C7 -0.1-µF, ceramic -

discC3 -2.2-µF, 10-WVDC, electrolyticC4 -1-µF, 10-WVDC, electrolyticC6-270-pE ceramic -discC8 -330-µF, 6-WVDC. electrolytic


B1 -9 -volt transistor radio batteryXTALI-3.2768-MHz crystalSl-SPST toggle or slide switchS2-DP3T rotary switch.11-Phono or BNC jackPrinted -circuit materials, enclosure

(Radio Shack 270-223 or simlar).9 -volt battery connector, #24 -gauge insulated stranded hook-upwire, solder, hardware, etc.

Note: The following parts areavailable from A. Caristi, 69 WhitePond Road, Waldwick, NJ 07463.Digital and counter boards, $11.95each; Ul, U2. U3, and U7. $2.00each; U4. U5, U6, $2.75 each;U8. $21.50. Please add $3.00postage/handling. New Jerseyresidents please add appropriatesales tax.

backplane signal, which is then fed toits connected decimal point when re-quired.

The lowest range, 20 kHz, requires

drive U8 (an ICM7224IPL high-perfor-mance 41/2 -digit counter) with inputsignals as low as .25 -volt rms.

Integrated circuit U8 contains a

W*4J- R1

220K

200kHz

20kHz 2MHz

64 DP 2MHz

1/4 CD40308 --7,,..-,\ ° . WR2* ± ...."

.... / 10

220K- -- -- S2 -b

S2 -a

FREQUENCY-- FREQUENCY

RANGE o 020kHz/ ..-

RANGE ----- '4_2MHz 200MHz

R3100K

C51

R61MEG

3

L14

CO40408

3 14

12

U1

LMC555CN

6

R710K

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J1

SIGNALINPUT

11

16 11

10

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U5CD4040B

16 11

1/4 CD403013

Ego 11 1

START 2 111)

STOP

1/4 CD4001B

1/4 CD4001B

GATE

14

10 U6 b1/2 CD451813

C7

.1

R81MEG

116-a

1/2 CD4518B

9 15 8

MA.R91K

02MPF102

R101K

C8

330 4

47052

16

RESET

C6

270pF "*"

R11

032N3908

R124.7K

32

R1347K

33 31

U8

ICM7224IPL

b d g c e f g abcd 9

29 134 35

BACKPLANE 1

27

3

20

35

21

34

22

7

23

6

24

5

26

36

25

37

13

30

14

29

15

11

16

10

17

9

19

31

18

32

6

25

7

24

8

15

9

14

10

13

12

26

11

27

37

21

38

20

39

19

40

18

2

17

4 3

22 23

DISP1LCD -004

16

12

Fig. 2. The circuit contains a crys al oscillator that's built around U3 -c and XTALI,which provides the primary timing -reference signal. That signal is then divided twiceto provide two additional timing references, giving the circuit three selectable timingreferences. 47

counter, decoders, output latches,and LCD display drivers. When thecount sequence is initiated by U1, U8 isreset to a count of zero by the narrow,differentiated, negative pulse fed toits reset terminal, pin 33. At the sametime, the positive gate pulse gener-ated by the flip-flop (U3 -a and U3 -b) isfed to pin 31, allowing U8 to accumu-late any pulses that appear at theclock input, pin 32.

The decoders and latch circuitswithin U8 are continuously enabled sothat the LCD readout provides an in-stantaneous indication of the accu-mulated count. That can easily bedemonstrated by applying a rela-tively low frequency, such as 100 Hz, tothe input of the counter. A steady dis-play of measured frequency is main-tained during the 1/2 to 1 -second timebetween trigger pulses, providing adigital readout similar to that of aDVM.

Counter U8 is capable of countingbeyond its full-scale display of 19999.That feature enables the circuit tomeasure frequencies aa high as 2 MHzwith a resolution of 1 Hz using thelowest scale of the circuit (1 secondgate time). That permits the four leastsignificant digits to properly indicatethe last four digits of the incoming fre-quency. If an overflow condition oc-curs, the most -significant digit of thedisplay remains 1.

The circuit is powered by a com-mon 9 -volt transistor -radio battery.Current consumption is about 7 milli-amperes, which allows 20 or morehours of operation using an alkalinebattery. A fixed 5 -volt regulator, U7, en-sures a constant power -supply volt-age to the entire circuit as theterminal voltage of the battery fallswith use.

Construction. The author's pro-totype of the frequency counter wasassembled on two printed -circuitboards, which the author refers to asthe digital board and the counter/dis-play board. Full-size templates of thecircuit -board patterns are shown inFig. 3 and Fig. 4, respectively. Partsplacement diagrams for the digitalboard and the counter/display boardare shown in Fig. 5 and Fig. 6, respec-tively,

When assembling the boards, besure that all parts are correctlyplaced, paying special attention to

2

19/is INCHES

Fig. 3. The author's prototype of thefrequency counter was assembled on twoprinted -circuit boards; the digital boardand the counter/display board. A full-size template of the digital board isshown here.

the polarized components. Doublecheck to be sure, since just one mis-placed component will result in aninoperative circuit and may causedamage to itself or other parts.

Assemble the digital board first,since it is the simplest of the twoboards. It is recommended that sock-ets be provided for all of the DIP IC's.Sockets are worth the small extra ex-pense should the circuit ever needservicing. Start by installing the appro-priate size IC sockets at the locations

indicated in Fig. 5. Do not install any ofthe IC's in their sockets until instructedto do so (which will be during thecheckout procedure). Don't forget toinstall the board's only jumper con-nection, which stretches from pin 6 ofU3 to pin 5 of U5. Figure 7 gives pinoutdiagrams for the three transistors andthe LCD readout listed in the Parts List.

After all the components havebeen installed on the digital board,connect a 9 -volt battery clip to theboard. Check the board for the usualconstruction errors; solder bridges,cold solder joints, misconnected ormisoriented components, etc. Oncethat is done, lay the digital board tothe side and go to work on the coun-ter/display board.

Turning your attenion to Fig. 6, notethat the counter/display board's as-sembly is a Iwo -part operation; com-ponent placement and jumperconnections. Separate placement di-agrams are provide for the two oper-ations; Fig. 6A for the componentplacements and off -board wiring,and 6B for the jumper connections.Socketing the LCD module is optional.If a socket is desired, one can be fab-ricated from a 40 -pin DIP socket bycutting it in half lengthwise. If you optto socket the display, use a wire -wraptype, since longer terminals will be re-quired to allow room for soldering thesocket to the copper side of theboard.

O0..

...

1- ......"0 scp0431

'/s INCHES

J

0

c. 0. .

Fig. 4. Here's the full-size template forthe counter/display board.

Begin the display -board assemblyby first installing a 40 -pin socket at theposition labeled U8. Then install all theboard -mounted components, asshown, with the exception of the dis-play (DISP1), which is indicated in Fig.6A by a dashed line. Because the dis-play (or a cut socket as mentioned) isto be mounted to the foil side of theboard, it must be installed last.

Once the board -mounted compo-nents (with the exception of DISP1)have been installed, connect thejumpers as shown in Fig. 6B. Be verycareful-there are 19 -jumper con-nections, making it very easy to mis-connect one or two. After installingthe jumpers, connect lengths of insu-lated hook-up wire (5- or 6 -inchlengths should be sufficient) to thepoints indicated for connection to thedigital board. Use shielded micro-phone wire (near C7) for connectionto the input jack, J1. Shielded micro-phone wire is specified for that con-nection to help prevent unwanted

B1

9V=MO

+5VTO

DISPLAYBOARD

- R6 -C1 I R7

C2

U7 I UI

C4

GROUNDTO

DISPLAYBOARD

C3

C5

as not to touch the component con-nections from the parts mounted tothe other side. It is necessary to han-dle things that way to provide suffi-cient room for soldering. Mountingthe display in that manner allows theboard assembly to be mounted di-rectly to the panel of the selected en-closure so that the readout can beviewed through a rectangular open-ing.

In any event, do not install the dis-play until the rest of the board hasbeen completely assembled, andchecked. Visually check your work,and then do a continuity check forpossible shorts, opens, bad solderjoints, and misconnected jumperwires. That precaution is necessarybecause if the display board has anassembly or wiring defect, it may benecessary to remove the LCD modulein order to repair the fault. If you findno defects in the assembly or the wir-ing, install the display.

Once that's done, begin preparing

BACKPLANERESET FROM

TO DISPLAY DISPLAYBOARD BOARD

-R3 --R4-

U2

200kHzDP TO ()-

DISPLAYBOARD

-R2-

2MHzDP TO

DISPLAYBOARD

XTAL I

- R5 -

U3 U4

GATE

-0 TODISPLAYBOARD

J

Fig. 5. Assemble the digital board first, guided by this parts placement diagram. It isrecommended that sockets be provided for all of the DIP IC's, and make sure that allparts are correctly placed, paying special attention to the polarized components.

pickup from the high -frequency cir-cuits in the unit. It's a good idea tolabel each wire as it's installed in orderto avoid confusion later when thewires are connected to the digitalboard.

Once all components, jumper con-nections, and lengths of wire are inplace, mount the display (or a cutsocket as mentioned) to the foil side ofthe board with enough elevation so

enclosure). The display board may beattached to the cover of the en-closure using suitable hardware.

In the author's protoytype, therange switch (S2) was mounted to thefront panel of the enclosure, just to theright side of the counter/displayboard. The power switch and inputjack were mounted to a side panel ofthe enclosure. It is best to mount J1 asclose to the board's input as possibleto reduce the length of the wire thatconnects J1 to the circuit board.

Once the project is completed, in-spect it thoroughly for any possiblewiring mistakes or bad solder joints. It isfar easier to correct a fault at this timerather than later on if you discoverthat your counter does not work.

Checkout. Checking out the counterwill require at least a digital voltmeteror VOM with an input resistance of 1megohm or more. A signal source,such as an audio or RF oscillator, or afunction generator, can be used to

200kHz

20k Hz

S2 -b

U5

the enclosure. The digital board wasdesigned to fit into the enclosure-which has molded PC slots-that isspecified in the Parts List. As for thedisplay board, it will be necessary tocut a 13/8- by 23/46 -inch rectangularopening into the cover through whichto view the readout. Try to keep thedisplay board more -or -less centered,top -to -bottom, to one side of the lid(which serves as the front panel of the

U6

provide an input signal to check theoperation of the counter on allranges. If necessary, a general-pur-pose oscilloscope may be required totroubleshoot the circuit in the eventthat it malfunctions.

At this point, there should be no IC'soccupying the DIP sockets. Connect afresh 9 -volt battery to the battery con-nector. Turn on the power and mea-sure the regulated DC voltage at the

GROUND

FROMDIGITAL 0-BOARD

R10 R12

RESETFROM 0DIGITAL

BOARD

J1

INPUT

BACKPLANE

o TO

DIGITALBOARD

GATE

FROMDIGITAL

BOARD

200kHzDP

FROM

DIGITAL

BOARD

2MHzDP

FROMDIGITAL

BOARD

I.C6

R13-C18+ I

R11

Cl1 I R9

R8 1

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DIGITALBOARD

DISP1*

U8

L

*SEE TEXT

A

J

J

J

-JJ

B

Fig. 6. Note that the counter/display board's assembly is a two-part operation;component placement (A) and jumper connections (B). Socketing the LCD module isoptional. If a socket is desired, one can be fabricated from a 40 -pin DIP socket bycutting it in half lengthwise.

output of U7. A reading of + 4.75 to+ 5.25 volts is normal. If an incorrectvoltage is indicated and the battery isdelivering at least 7 volts to the circuit,troubleshoot the circuit and repair thefault before proceeding with thecheckout.

Check the orientation of U7. Withthe battery disconnected, measurethe resistance between the + 5 -voltbus and ground to make certain thatthere is no short circuit in the wiring. A

normal indication is 1000 ohms ormore. Any reading that's much lowerthan that indicates a short or defec-tive component. After the fault hasbeen located and corrected, and the5 -volt regulated supply is operatingproperly, continue with the checkout.

Remove power from the circuit, andinsert the IC's into their respectivesockets. Be careful to orient eachproperly, and make sure that they areproperly seated. Set the range switch

to 2 MHz. With no signal applied to theinput jack, apply power to the circuitand observe the display. After thepower has been on for at least a sec-ond, you should get a 000.0 indica-tion. Set the range switch to 200 kHz.This time the display should read00.00. Set the range switch to 20 kHz,and the display should now show0000.

If the unit does not give the correctdisplays, troubleshoot the circuit be-fore proceeding. The display shouldindicate the probable area of fault.For example, if the digits are acti-vated, but do not form perfect zeros,the fault probably lies with the wiringof the associated segments that areincorrect. The same comment holdsfor the decimal points. If the display istotally blank, check that the LCD mod-ule is installed correctly.

A totally blank display can also becaused by lack of backplane signalgenerated at U8 pin 5. Check the wir-ing associated with pin 5 to be surethat it is not open, or shorted. An os-cilloscope may be used to verify thepresence of the backplane signal,which is a 5 volt peak -to peak square -

ofU5 for the proper 5 -volt input. Check

BOTTOMVIEW

DEVICEPIN FUNCTION

1 2 3

AN78L05 (U7) 0 G I

6S170(01) D G S

MPF102 (02) S D 0

0N3908 (03) E B C

40

A

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 21

innI 0 1_71n

11111111111111111111 20LCD -004

TOP VIEW

B

Fig. 7. Here are the pinout diagrams forthe three transistors and the LCDreadout listed in the Parts List.

(Continued on page 107}

Todays consumers are offeredan ever increasing variety ofwireless gadgets, many of

which operate in the 46- and 49 -MHzFM bands. Walkie-talkies and cordlesstelephones are but two examples ofthat. Operating those gizmos is usuallyvery easy. But simply operating themteaches you relatively little aboutwhat makes them tick. One way tolearn about how such devices work isto build, maintain, and repair a few ofthose wireless 'thingamajigs."

In this article, we are going to showyou how to build a low -power trans-mitter that can be used with any corn-patible receiver: cordless telephones,walkie-talkies, baby monitors, etc. The49 -MHz FM Transmitter described inthis article, which is powered from astandard 9 -volt battery, is capable ofoutputting 16 mW (milliwatts) of RFpower. The circuit contains a voltage -controlled crystal oscillator (VCXO) to

Build a49 -MHzFM Transmitter

Learn some of the principles behind wirelesscommunications by building this simpleFM transmitter

BY DAN BECKER

ensure RF-carrier stability. That helpsto prevent signal drift.

In a frequency -modulated (FM)transmission, the RF carrier frequency[49.890 MHz in our case) must deviate(vary) in direct proportion to the am-plitude of the audio or voice signal.

Circuit Description. Figure 1 is aschematic diagram of the 49 -MHz FMTransmitter. The circuit consists of anaudio amplifier, a low-pass filter, threeRF stages, and a regulated -DC powersupply.

The audio picked up by the micro-phone (MIC1) is fed to U2 -a (half of anLM358 dual op -amp), which is config-ured as a non -inverting audio ampli-fier, the gain of which (approximately500) is determined by R1 and R28. Ca-pacitor C6 modifies the gain of theaudio amplifier, effectively turning itinto a high-pass filter. That results in a13 -dB gain at 100 Hz that increases 6 -dB -per -octave to yield 33 dB at 1000Hz.

In order to keep the audio band-width below 20 kHz ( + /-10 kHz), theoutput of U2 -a is fed to a low-passfilter, consisting of R7/C9. Together thelow-pass filter and audio amplifieryield an overall cutoff frequency ofabout 4 kHz. The resulting signal is thencoupled through R8 and R9 to thebase of Q1 ---a buffer stage builtaround a 2N3904 general-purposeNPN transistor that's configured as aboot -strapped voltage follower. Theoutput Q1 is fed back via C11 to theR8/R9 junction; that prevents Q1 fromloading the low-pass filter.

The output of Q1 (taken from itsemitter) is fed through R10 (which pro-vides a means of adjusting the peakdeviation) to a crystal -controlled Col-pitts oscillator comprised of Q2, L1, D1,XTAL1, and several support compo-nents. Figure 2 shows a simplifiedschematic diagram of a Colpitts os-cillator. In that circuit, capacitors C16and C17 and inductor L provide feed-back to Q2's input. However, a feed-

back network made with a conven-tional inductor would have a Q(quality factor) well below 100, allow-ing oscillation over a wide band offrequencies. That would make theoutput signal very unstable. To in-crease the oscillator's tuning sharp-ness (Q) and, by extension, itsfrequency stability, a quartz -crystalresonator is used. Inductor L repre-sents the net result of three separatecomponents: crystal XTAL1, tuning coilL1, and varactor diode Dl.

The operation of a quartz crystal isbest explained by a simplified equiv-alent circuit, like the one shown in Fig.3. That model consists of a series -reso-nator network made up of Cm, Lm,and Rm, with a parallel capacitor, Co,shunting the crystal's terminals. At thecrystal's series -resonant frequency,the equal 'and opposite reactancesof Cm and Lm cancel each other out,leaving the equivalent series resis-tance Rm.

However, our Colpitts oscillator re-quires an inductor between C16 andC17. Therefore, as with any series -res-onant circuit, as the applied signalincreases in frequency, inductive re-actance dominates. Therefore, thecrystal resonator is manufactured sothat the desired operating frequencyis slightly above the crystal's series -res-onant frequency. That provides theneeded inductor, but one with a Q ofseveral thousand, which sharply tunesthe feedback network to a single fre-quency.

Refer back to Fig. 1. In order to gen-erate an FM signal, it is necessary tomodulate the oscillator's frequency.The audio signal from the micro-phone is used as the modulatingsource. Diode D1, with a junction ca-pacitance that's inversely propor-tional to the voltage between itsanode and cathode, provides a con-venient mechanism for varying the

+9V

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R112K

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16.630MHz-'IJF

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100KR2 $

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C5 R3100pF 100K1

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C24.001

Fig. 1. The 49 -MHz FM Transmitter consists of an audio amplifier, a low-pass filter,three RF stages, and a regulated -DC power supply.

Fig. 2. Shown here is a simplifiedschematic diagram of a Colpittsoscillator. In that circuit, capacitors CI6and C17 and inductor L providefeedback to Q2's input. Inductor Lrepresents the net result of three separatecomponents: crystal XTAL1, tuning coilLI, and varactor diode DI.

R245652

RF AMP (FINAL)

Fig. 3. The operation of a quartz crystalis best explained through this simplifiedequivalent circuit, consisting of a series -resonator network made up of Cm, Lm,and Rm, with a parallel capacitor, CO,shunting the crystal's terminals.

resonant frequency of the oscillatorsfeedback network.

However, since D1 lowers the netinductive reactance of the crystal, L1is included in the circuit to compen-sate for the loss. Inductor L1 can alsobe used to'adjust the oscillator to the

C27.001

C2818pF

desired center frequency. Resistor R27lowers the Q of Ll, preventing spuriousoscillations that may be caused by L1resonating with the crystal's shunt ca-pacitance.

Voltage divider R12/R13, along witha pair of low-pass filters (consisting ofR14 and C14, and R15 and C15), setDl's quiescent point to 3 volts; thatyields a junction capacitance (whichvaries by about 2-pF/volt of audio sig-nal) of approximately 16 pF. Thus theaudio -signal frequency modulatesthe oscillator. Because it is easier tovary the frequency of a 16 -MHz crystaloscillator than that of a 49 -MHz crystaloscillator, the circuit operates on thethird sub -harmonic of the output fre-

quency. For example, if a 49.890 -MHztransmitter signal is desired, a 16.630 -MHz crystal would be selected. Be-cause 02's output is rich in harmonics,the next stage is tuned so that it ampli-fies only the third harmonic (49.890MHz) and ignores the 16.630 -MHz fun-damental frequency.

Since the third harmonic producesthree times as much deviation as theoscillator's fundamental frequency,varying the fundamental frequencyby + /-1.67 kHz yields a + /-5 kHz devia-tion at 49.890 MHz. That greatly re-duces the demand on our reactancemodulator. The output of oscillator isfed to the emitter -base junction of 03(an RF driver stage) through C19. Bymaking C19 small (47 pF), 03's lowinput impedance does not load ordetune the oscillator. ResistorsR21-R23 set 03's quiescent DC emit-ter current to a fraction of a milliamp.However, drive from 02 automaticallyincreases that current to a few milli -amps, producing significant RF-power gain. Capacitors C20 and C21bypass RF current to prevent degen-erative feedback.

A resonant tank circuit, comprisedof T1 and C23, filters Q3's highly dis-torted collector current by creating ahigh impedance at 49 -MHz, but a lowimpedance at the oscillator's funda-mental and second harmonic. Thatallows Q3's collector to drive 04 with areasonably clean, 49.890 -MHz signalthrough C23. The next RF-outputstage, built around Q4, works prettymuch like the 03 driver stage. How-ever, DC bias resistors R24 --R26 arenoticeably smaller than their 03counterparts. That causes a larger DCemitter current, and results in greaterRF gain.

As with Q3, a resonant -tank circuit(consisting of T2 and C26) filters Q4'ssomewhat -distorted collector cur-rent. A reasonably clean output signalis taken from Q4's collector, and usedto drive the antenna. The antenna -loading coil, L2, is used to tune outcapacitive reactance, allowing 04 tosee a more resistive load. CapacitorC27 blocks Q4's DC collector voltage,while coupling its RF output to the an-tenna. Capacitor C28 improves theimpedance match between 04's out-put and the antenna, in addition tosuppressing any spurious VHF emis-sions.

Power for the circuit is supplied by a

PARTS LIST FOR THE49-MHZ FM TRANSMITTER

SEMICONDUCTORSU I-AN78L06 6 -volt, 100-mA, low -

power voltage regulator, integratedcircuit

U2-LM358N low -power dual op -amp, integrated circuit

Ql. Q2, Q3 -2N3904 general-purpose NPN silicon transistor

Q4-2SC1687 RF-amplifier, NPNsilicon transistor

Dl-MV2105, 15pF at 4 -volts,varactor tuning diode (Motorola)

RESISTORS(All fixed resistors are 1/4 -watt, 5'4

units, unless otherwise noted.)R1-1-megohmR2, R26 -220 -ohmR3, R4, R14, RI5, R25 -100,000 -

ohmR5, R6, RI I -20(X) -ohmR7 -22,000 -ohmR8 -82,000 -ohmR9 -47,(X)0 -ohmR10 -10.000 -ohm. trimmer

potentiometerR12. R13 -10.000 -ohm, V%RIO, R19--10,000-ohmRI7-680-ohmR18-16,000-ohniR20 -100 -ohmR21 -1000 -ohmR22 -330,000 -ohmR23 -560 -ohmR24 -56 -ohmR27-I2,000-ohmR28--2(XX)-ohm

CAPACITORSCI, C2, C14. C18. C2I, C25, C29-

0.01-p.E, ceramic -discC3, C13 -10 -RE 16-WVDC,

tantalumC4. C28-18-pE ceramic -discC5-100-pF, ceramic -discC6-0.0068-p.E metallized -filmC7. C12--0.l-p.F. metallized -filmC8 47-11E 16-WVDC, electrolyticC9 0.0039-pf, metallized -filmCIO, C16-150-pE ceramic -discCI I-0.00824LE metallized -filmC15. C20. C24, C27-0.001-p.F,

ceramic -discC17-120-pE ceramic -discC19, C23-47-pE ceramic -discC22. C26--24-pE ceramic -disc


LI-TK1414 3.3-0, 7.96 MHzToko coil

L2-TK1601 I.6-p.H, 25.2 -MHzToko antenna -loading coil

Ti. T2-TKI407 0.41-p.H, 49 -MHzToko RF transformer

MICI-Electret microphone elementXTAL1-16.630-MHz, 32-pF

parallel -resonant crystalBI -9 -volt alkaline transistor -radio

batterySI-SPST momentary contact

pushbutton switchPrinted -circuit materials. antenna (27 -

inch whip or length of #22 wire).enclosure, 8 -pin DIP socket, wire,solder, hardware, etc.

9 -volt battery (B1). Alternatively, the cir-cuit can be operated from any 9 -voltDC source that's capable of supplyingabout 20 mA or so.

When S1 is pressed, 9 -volts DC is ap-plied across C1 to voltage regulatorU1. Capacitor C1 protects U1's inputfrom stray RF and voltage spikes. Inte-grated -circuit U1 regulates its 9 -volt in-put to deliver 6 -volts DC to all of thecircuit except for the RF driver andfinal stages. If a regulator were notused, the RF carrier frequency coulddrift or change as the battery voltagedecreased with age. Capacitors C2and C3 minimize the noise and volt-age spikes that are often generatedby low-cost voltage regulators like U1.

Construction. The author's pro-totype was assembled on a printed -circuit board that measures about

115/16 by 2 inches. A full-size templateof the printed -circuit artwork is shownin Fig. 4. Once you've etched yourown board and gathered the partslisted in the Parts List, construction canbegin. Most of the specified compo-nent values are not critical; so if yourjunkbox contains a reasonably closevalue to the one specified, use it. If youhave a reasonably well -stocked partsbin, you probably already have morethan half (if not all) of the passivecomponents.

A parts -placement diagram for theprinted -circuit board is shown in Fig. 5.It is recommended that an IC socketbe provided for U2. Before you beginassembling the project, it is importantthat you decide at what frequencythe circuit is to operate. The frequen-cies shown in Table 1 correspond tothe 46- and 49 -MHz cordless-tele-

[4-115/11 INCHES

Fig. 4. The author's prototype wasassembled on a printed -circuit boardthat measures about 1"/IO by 2 inches.This full-size template of the printed -circuit artwork is provided so that youcan etch your own printed -circuit board.

phone channels. However, many ofthose frequencies are also used bywalkie-talkies, baby monitors, and nu-merous other wireless and experi-mental devices. To determine therequired crystal frequency for thetransmitter, divide the given channelfrequency by three.

Once you've decided on the fre-quency of operation for your transmit-ter and obtained the required crystal,assembly can begin. Start by installingan IC socket where U2 is indicated inFig. 5, and then install the passivecomponents surrounding the socket.When assembling the circuit, mountall of the components close to thecircuit board to keep lead length(and thus its reactance) to a mini -

O mum. Note: Because of the density in0co component placement, most of the

resistors are mounted vertically.Also note that except for the three

cn electrolytic and the two metallized -(1) film capacitors, all of the capacitors>-m are low -voltage ceramic -disc units.o Affer the passive components have

been installed, mount and solder thecnQ semiconductors in place. ConnectO the positive lead of the battery con-= nector in series with a SPST switch,

J making sure that that subassemblyw has sufficient (but not over abundant)cr) lead length to reach the switch'sCD

mounting location. Connect that sub -54 assembly to the points on the board

shown in Fig. 5. Finally, connectlengths of wire to the board whereMIC1 and ANTI are indicated.

The next step is to prepare the en-closure. Any enclosure of sufficient sizecan be used to house the 49 -MHz FMTransmitter; just remember that theenclosure should have sufficient roomto accommodate the circuit board aswell as the off -board components (S1,ANTI, B1, and MIC1).

The first step in preparing the en-closure is to select a site on or withinthe enclosure for the off -board com-

61I

T

S1

L2

028

1026

ANTI

T2

MIC1

-R24--C24-

R25 C25

RB R5 29

R3 -C7-

-05-C4 R1

R28

-06-

U2

023

T1

-C21--C18-

F04

R15

-C14--C15-

Cr

-R2-+

Cal -R7-

TABLE 1-FREQUENCY ALLOCATION

CHANNELBASE

TRANSMITTER(MHz)

HANDSETTRANSMITTER

(MHz)

1 46.610 49.6702 46.630 49.8453 46.670 49.8604 46.710 49.7705 46.730 49.8756 46.770 49.8307 46.830 49.8908 46.870 49.9309 46.930 49 99010 46.970 49.970

01

-C20- R21 LiCi9C16R17Ri8Q3D

C17

1122 3 R19

R20XIAL1

HOF-

Ll

-Rle

1

C11

H10

D. 010

-C9-

Fig. 5. Assemble the printed -circuit board using this parts -placement diagram as aguide. It is recommended that an IC socket be provided for U2. Before you beginassembling the project, however, it is important that you decide on what frequency thecircuit is to operate and to select a crystal accordingly.

ponents-S1, MIC1, and ANTI. Drillholes at the selected sites for the com-ponents that will be located there.Mount the off -board components tothe enclosure, and connect them tothe circuit using the previously in-stalled hook-up wire.

Note: If you intend to power the cir-cuit from an alternate power source

(a wall adapter, for example), install a10-0 miniature RF choke in serieswith each supply lead, and then con-nect the positive lead in series with anSPST switch.

If you intend to use a telescopingwhip antenna, be certain that it in-cludes mounting hardware. Most


Most companies use thesame type of telephone forall of their employees, all of

which sound the same when theyring. The result? Every time a phonerings, two or three people can beseen running back to their office tosee if it is theirs. You only have threerings to get the call, or it switches tothe department secretary. If it wasn'tso darn frustrating, it would be com-ical.

You can put a stop to all that undig-nified exercise by building the Tele-phone Ring Converter. It is a simpleone -evening project that will changethe ring of your telephone to an elec-tronic warble (usually found on ex-pensive multi -line telephones). Thepitch of the warble signal is adjusta-ble, so you can change the note ofyour telephone to make it sound dis-tinct from your neighbor's. The projectcan also be used to indicate thatthere is an incoming call in placeswhere you don't have a phone (suchas a workshop).

How it Works. The schematic di-agram for the ring converter is shownin Fig. 1. The circuit is based on theTCM1506 ring detector/driver inte-grated circuit. It is a monolithic IC spe-cifically designed to replace thetelephone's mechanical bell. Thechip is powered and activated by thetelephone -line ring voltage, whichmay vary from 40-150 volts rms at afrequency of from 15 to 68 Hz. Noother source of power is required.

Telephone RingConverter

BY DEAN F. POETH, II K8TM

This one -evening project alters the ringingsound of your phone so you can

distinguish it from any other phone in the room.

Again referring to Fig. 1, C1-05 areplaced in parallel to form a 0.5-1.LFcapacitor that conducts the AC ringvoltage to pin 1 of the TCM1506, butblocks any DC component. Of course,those capacitors can be replaced bya single 0.47-0.5-ILF capacitor pro-vided it has at least a 400-WVDC rat-ing. Resistor R1 is in series with thecapacitor network and is used to dissi-pate power from any high -voltagetransient that might appear acrossthe line. The diluted AC voltage thatreaches pin 1 on U1 powers the chip.

Capacitor C6 is used to prevent"bell tapping." That is an annoyingringing of the bell that occurs when aphone on the same line is used to dialan outgoing call. The capacitor pre-vents the short dial pulses from trig-gering the ring detector, but still allowsthe much longer ring signal to acti-vate it.

Potentiometer R2 is used to vary thetone of the ring signal from below 100Hz to over 15 kHz. Potentiometer R4 isthe volume control; adjusting that po-tentiometer to its lowest resistance willmute the piezo element (BZ1).

When a ring signal is present on thephone -line, it powers U1. The IC thengenerates a tone (with a frequencydetermined by R2 and an amplitudeset by R4) that is reproduced by BZ1.

Construction. Construction is

straightforward and the parts layout isnot critical. Any point-to-point wiring

technique will do. However, a printed -circuit board was used in the pro-totype to speed-up construction andto prevent wiring errors. If you wish tomake a printed -circuit board, use thefoil pattern shown in Fig. 2.

If you plan to use the foil pattern,take a look at the parts -placementdiagram shown in Fig. 3. As you cansee, to obtain the 0.5-RF capacitancefive 0.1-µF capacitors are wired inparallel; however, note that capaci-tors C2 and C4 are mounted on thefoil side of the board to save space.

Regardless of the wiring techniqueyou use, a socket is recommended forthe IC to prevent heat and staticdamage while soldering. It's also agood idea to leave the integrated cir-cuit in ifs conductive packing until youare ready to install it.

Once you've mounted all the on-board components, attach leads tothe off -board components asneeded and solder the leads to theappropriate points on the board.Those points are shown in Fig. 3.

You will now have to attach a mod-ular extension cord to the circuitboard. The one you use will dependon whether you wish to use the projectto change the pitch of a phone or justto act as an annunciator where thereis no phone.

To use the project along with aphone, you will need a telephone ex-tension cord with a dual -female end.That will permit you to connect it to the 55

C1

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C3

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BZ1

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C6VOLUMER2

1MEGA

R3

TONE 1MEG

Fig. I. The Ring Converter circuit is incredibly simple thanks to the ring detector/driver IC, which does all the work. It even runs off the ring signal making aseparate power supply unnecessary.

1* --13/16 INCHES

Fig. 2. If you wish to build a RingConverter on a piece of printed -circuitboard, use this pattern to etch the foil.

C1

C2'

R2

FI3

C3

C4*

C5

U1

J

C6

TOPHONELINE

H4

*LOCATED ON FOIL SIDE

Fig. 3. Use this parts -placementdiagram as a guide when mountingcomponents on the circuit board. Notethat you will need to attach leadsto the two potentiometers (R2 and R4) toconnect them to the board.

phone line and telephone as shownin Fig. 4A. Note that the set-up alsorequires a modular extension with amale connector on each end. Pro -

TELEPHONEWALL JACK

DOUBLEMODULAR

JACK END OFTELEPHONEEXTENSION MODULAR

CORD TELEPHONEPLUG

0 p 6THE RING CONVERTER

0 6THE RING CONVERTER

To minimize the surface area of the PCboard, capacitors C2 and C4 have beenplaced on the foil side of the board.Soldering them in is a little tricky, but itsaves a lot of space.

A

B

MODULAR LINE CORD

TELEPHONE

TELEPHONEWALL JACK

MODULAR TELEPHONEPLUG END OF TELEPHONE

EXTENSION CORD

Fig. 4. You will have to wire an appropriate cable to the Ring Converter dependingon whether you will use it with a nearby phone (A), or in a remote location as anannunciator (B).

vided you have a modular crimpingtool, you can kill two birds with onestone: Just buy a modular extensioncord that has a dual -female con-nector at one end and a male con-nector at the other. Cut the extensionin half, strip the cut end of the halfsporting the dual connector, and at-tach the green and red leads to thecircuit board. Take the half with themale connectot and add anothermale connector to the cut end. Onceyou've tested the unit (more on that

shortly) you can connect the projectfollowing Fig. 4A.

To use the project as a simple an-nunciator in a location without aphone, you just need a male plug onone end of a length of telephonewire. If you wish, you can use a tele-phone extension cord with one endsnipped of. Connect the leads at thefree end to the circuit, and onceyou've tested the unit, plug it into awall jack as shown in Fig. 4B.

(Continued from page 112)

BY ANTHONY J. CARISTI

Anyone who has been blessedwith a new infant knows howimportant it is to keep a con-

stant watch on your progeny. That'sespecially true when the baby is fastasleep in his or her crib; a time whenone must be particularly vigilant. Thecircuit described in this article-dub-bed the Baby Alert-is a simple elec-tronic project that allows you tomonitor the baby's room without hav-ing to be within earshot.

The project consists of a carrier -cur-rent transmitter and a receiver. Thetransmitter, which plugs into any ACoutlet in the baby's room, generatesan electronic signal when the babycries. That signal is sent through the ACline and is picked up by the receiver,which can be plugged into any outletwithin the home. Transmitter portionof the project is sensitive enough todetect sound that cannot easily beheard through a closed bedroomdoor, so even faint cries can be de-tected. It is also useful at night whenyou're asleep and may not easily hearthe baby cry. If desired, multiple re-ceivers can be placed at various lo-cations throughout your home andbe simultaneously active.

BABY MONITORKeep a constant "watch" on your progeny from any-where in your home with this carrier -current system

The Baby Alert can also be a valu-able aid to the hearing impaired. Or itmight be used to monitor an area forsound, perhaps as part of a securitysystem-any sound made by an in-truder would activate an alarm. Itmight also be used to extend therange of the doorbell (sort of a door-bell relay station).

Transmitter Operation. Figure 1shows a schematic diagram of thetransmitter portion of the project. Op-erating power for the circuit is deriveddirectly from the AC line. DC power tooperate the circuit is generated in twostages, one for an RF power -amplifierstage, and the second for the re-mainder of the circuit.

The AC line voltage is applied to D1,which half -wave rectifies the AC input.The resulting DC voltage (approxi-mately 30 volts under load) is fedacross an RC filter (comprised of R1and C1) and used to operate ampli-fier, Q1. The second stage of the

power supply (composed of LED1, R2,D2, D3, C2, and C3, which forms aregulated + 13.6 -volt, center -tappedsupply) feeds the remainder of thecircuit. LED1 is connected in series withR2 and is used as a visual power -onindicator for the transmitter.

An electret microphone element(MIC1) is used as the pick-up. The out-put of the microphone is AC coup:edthrough C5 to U1 -a (a non -invertingop -amp with a gain of about 100). Theoutput of U1 -a at pin 1 is AC coupledthrough C4 to the non -inverting inputof U1 -b (which provides an additionalgain of 48) at pin 5. The output of U1 -bat pin 7 is then fed through D4 andR10, and across R11 and C6 to theinverting input of U1 -c, which is config-ured as a voltage comparator. Thenon -inverting input of U1 -c is biased toa positive voltage that is set by SENSITMTY

-control R19. This represents a thresh-old voltage at which the output of U1 -c switches from high to low.

During standby, the output of U1 -c

.22

4 1 101

117 HOT D1

VAC 1N4004{NEUT.

+6.8V

R1

1K

3WATTA,

- C147

R2

3.3K3WATTAM

D21N4736A

6.8V

13.6V

R310K

2

R4

10K 3

{ R510K

MIC1 "=

R1920K

SENSITIVITY-L

U 1 -a

C501

R7wt. 10K 16_R6

C41MEG

.01

1/4 LM324N

D31N4736A

6.8V

C2 1.+470

C3

470 T

cos olso 0

10 2

I 1ND41448K 5

R9470K

U1 -b

1/4 LM324NR8

10Kt R10

22K

0

R11

100KC6

4

U1 -c8 2

4

R12100K

8

1/4 LM324N11

U2LMC555CN

3

7

6

C7

1% 10

U3

LMC555CN

WVR1310K

2 6

7

r0'131511rarcro,T1

TK1901

K

-L

C8

.033

R144.75K

WV

R164.7K

4/4/*

\AAR15

2.21K

Fig. I. The Baby Alert transmitter is built around an LM324 quad op -amp (UI), twoLMC555CN CMOS oscillator/timers (U2 and U3), and a few support components.

at pin 8 is held at about 12 volts whenthe voltage developed across C6 isless than the bias -voltage setting atpin 10. When a sound of sufficient in-tensity and duration is detected, thevoltage at pin 9 of U1 -c exceeds thethreshold level (set by R19), causingU1-c's output at pin 8 to go low. Thatlow is applied to pin 2 of U2 (a 555oscillator/timer that's configured as amonostable multivibrator). Thatcauses the output of U2 to go high forabout one second, as determined bythe time constant of R12 and C7. Theoutput of U2 at pin 3 is applied to pin 4of U3 (a second 555 oscillator/timerthat is configured for astable opera-tion, with a frequency of about 125kHz). That causes U3 to oscillate, pro-ducing a near squarewave outputthat is used to drive Q1 into con-duction. The output of Q1 is appliedacross a parallel -tuned circuit com-posed of TVs primary and C8. Thetuned circuit, in turn, reshapes the 125 -kHz signal, causing a sinewave-likesignal to appear across both the pri-mary and the secondary of T1.

The signal appearing at T1's sec-

ondary (about 1 or 2 volts peak -to -peak) is impressed across the ACpower line, and is then distributedthroughout the building without af-fecting other electrical appliancesconnected to the line. Transient sup-pressor D7 is included in the circuit tohelp protect Q1 from voltage spikesthat might appear across the powerline and be coupled to the circuitthrough T1.

Receiver Operation. Refer to Fig. 2,the schematic diagram of the BabyAlert receiver. Power for the receiver,as with the transmitter, is derived froma traditional half -wave rectifier (D5).The resulting DC voltage is regulatedto 27 volts by D6 and R20, and thenfiltered by C11 to provide a relativelyclean, DC power source for the circuit.A light -emitting diode, LED2, con-nected in series with R20 provides avisual indication that the circuit ispowered and ready to receive a sig-nal.

The 125 -kHz signal is plucked fromthe AC line and coupled through R21and C12 to a parallel -tuned LC circuit,

C9.001

R181000

tt R171000

(E) 01MPSA42

D7P7055

consisting of C13 and L1. That LC cir-cuit passes 125 -kHz signals while at-tenuating all others. The 125 -kHz signalis fed through C14 to the base of Q2(which is configured as a high -gainlinear amplifier), which boosts the rel-atively low amplitude of the 125 -kHzsignal. The RF output of Q2 is AC cou-pled to the base of Q3 through C15.Transistor Q3 acts as both an amplifierand detector. Since there is no biasvoltage applied to the base of Q3, itremains cut off until driven by the am-plified 125 -kHz signal. When Q3 is for-ward biased, its collector voltagerises.

Capacitor C16, connected acrossQ3's collector resistor, filters the 125 -kHz signal so that it is essentially DC.When the voltage at the collector ofQ3 rises, Q4 is driven into conduction.That causes current to flow into piezobuzzer BZ1, producing a distinctive au-dio tone that alerts anyone within ear-shot that the baby needs attention.

Construction. The author's pro-totype was assembled on a pair ofprinted -circuit boards. Full-size tem-

plates of the two circuit -board layoutsare shown in Figs. 3 (the transmitter)and 4 (the receiver). You may etchyour own boards using the templatesor obtain a set from the source givenin the Parts List, Once you have a set ofboards, assemble the transmitter andreceiver boards guided by Fig. 5 and6 (respectively).

It is recommended that sockets beused for all IC's; it is well worth theadditional cost should the circuit everrequire troubleshooting. Be very care-ful to orient all polarized compo-nents-such as transistors, diodes,integrated circuits, and electrolyticcapacitors as shown in the parts -placement diagram. A single mis-oriented component will render thecircuit inoperative and may causedamage to itself, or to other compo-nents

Resistors R1 and R2 in the transmitterand R20 in the receiver normally op-erate at temperatures that are verywarm to the touch. Be sure that thosecomponents are allowed sufficientclearance from all other compo-nents, the sides and top of the en-closure, and the board itself. Capaci-tors C8 and C9 in the transmitter andC13 in the receiver are tuning compo-nents (which are part of frequency -selective networks). Because of that,use only the component types spec-ified in the Parts List. Ordinary ceramiccapacitors are not temperature sta-ble and should not be used in placeof the specified parts. The same con-sideration holds true for R14 and R15 inthe transmitter. Use only metal -film re-sistors where directed; carbon typesare not stable with temperature andshould not be used in those locations.

Transistor Q1 and some of the ca-pacitors used in both the transmitterand the receiver have higher voltageratings than ordinarily found in solid-state circuits. Be sure to use parts thathave the specified voltage rating.Note that U2 and U3 (in the transmit-ter) are the CMOS version of the com-mon 555 oscillator/timer. Use only thespecified parts; the ordinary 555 maynot operate properly at the specifiedtransmitter frequency (125 kHz).

Before mounting T1 to the transmit-ter board, use an ohmmeter to identi-fy the primary, which is connected toterminals 3 and 4 and electrically iso-lated from the secondary. Secondaryterminals 1 and 5 are used in this cir-

117

VAC

HOT

NEUT.

WD5 R20

1N4004 3.3K3WATT

R21

10K

C12

''.001

C13001

C14.001

IE

D61N4750A

27V

C11

0- 470

=1=R22 t4.7K

R23470K

L1

4.

11 5mH

TK3203

R25100K

C152N3904

.01

02

C16±.01 t R24 C17

10052 2.2

032N3906

t R264.7K

R284.7K

41s01,

R2747K

BZ1

042N3904

R2910K

Fig. 2. The Baby Alert receiver is comprised of three transistors-Q2, which isconfigured as a high -gain linear amplifier; Q3, which serves as both an amplifier anddetector; and Q4, which is essentially used as a switch-and a few additionalcomponents.

Fig. 3. Here is a full-size template of the transmitter's printed -circuit board.

cult; 2 and 6 are not. When you havecompletely assembled the boards,examine them very carefully for coldsolder joints; they appear as dull blobsof solder. Correct any joint that is sus-pect. Also check for opens and inad-vertent short circuits between adja-cent traces. Most problems can beattributed to faults such as those; it isfar easier to correct them at this stagerather than later.

Both the transmitter and the re-ceiver are powered directly from theAC line without transformer isolation.AC power receptacles have twopower leads, one "hot" and the other"cold" (sometimes called neutral) thatare generally color -coded black andwhite, respectively. The cold lead isessentially at ground potential, while

the hot lead is 117 volts above ground.It is recommended that only polar-

ized power cords, either 2- or 3 -con-ductor types, be used for both circuits.The larger spade of a polarized plug isneutral and smaller one is hot; thesame hold true for three -conductorplugs, with the third terminal beingEarth ground. In any event, connectthe hot and neutral leads of thepower cord to the points indicated inthe parts -placement diagrams (Figs.5 and 6). Secure the cord so that theexposed ends cannot move and ac-cidentally touch your body or any-thing else.

Enclosure. Once the leads of thepower cords have been connectedto the transmitter and receiver, it is

Vile INCHES

1 time to consider the enclosures thatwill house the two circuit boards.WARNING: It is mandatory that themicrophone element be mountedcompletely inside the transmitter's en-closure so that there is absolutely nopossibility of anyone (including the in-fant) coming in contact with it. Themetal shell of the element is con-nected to one side of the power line,and could represent a shock hazard.

Since both transmitter and receiverare directly connected to the AC

Fig. 4. This is a full-size template of thereceiver's printed -circuit board.

MIC1

ILL ii117VAC {

C6

-R11-

05

R19 -R10-

18 .04U1

R5 -R6-

NEUT

HOT

power line with no isolation, it is rec-ommended that 100% plastic cab-inets be used to house bothassemblies, thereby eliminating a

-C10-

Fig. 5. Assembly the transmitter's printed -circuit board using this parts -placementdiagram as a guide. When assembling the transmitter, it is recommended that socketsbe used for the IC's.

NEUT.

{117VACHOT

-C13-

Cl2IR21 L1

olD6

D5

C1I4

C11

--- R22- C17

C16

Q3

R20

R27

Fig. 6. Use this parts -placement diagram as a guide to assembling the receiver'sprinted -circuit board. It is important that only polarized power cords, either 2- or 3 -conductor types, be used to connect either circuit board to the AC line. The largerspade of a polarized plug is neutral and smaller one is hot; in a three conductor plug,the third terminal is Earth ground.

PARTS LIST FOR THEBABY ALERT TRANSMITTER

SEMICONDUCTORSU1----LM324N quad op -amp.

integrated circuitU2, U3-LMC555CN CMOS

oscillator/timer, integrated circuitQI-MPSA42 or equivalent high -

voltage NPN silicon transistorDI-IN4004 I -amp, 400-PIV silicon

rectifier diodeD2, D3---IN4736A 6.8 -volt, I -watt,

"Loner diodeIN4148 general-purpose silicon

diodeD7 -P7055 transient suppressor

(Digi-Key)LEDI-Light-emitting diode, 2 -volt,

20-mA

RESISTORS(All fixed resistors are 1/4 -watt, 5C1c

carbon units, unless otherwisenoted.)

RI -1000 -ohm, 3 -watt, metal -oxideR2 -3300 -ohm, 3 -watt, metal -oxideR3 -R5, R7, R8, R13---10,000-ohmR6-1- megohmR9 -470,000 -ohmR10--22,000-ohmR 1 1 , R12--100,000-ohmR14 -4750 -ohm 'A -watt, I% metal -

filmR15 -2210 -ohm, 1/4 -watt, 1% metal -

filmR16--4700-ohmRI7, R18 -100 -ohmRI9--20,000-ohm, PC -mount

potentiometer

CAPACITORSCI -47-11F, 100- WV DC . electrolyticC2, C3--470-µF, 10-WVDC.

electrolyticC4, C5 0.01-µF, 50-WVDC,

ceramic -discC6 -1-11F, 10-WVDC. electrolyticC7-10-p.F. I6-WVDC. electrolyticC8 0.033 -RE 50-WVDC,

metallized -filmC9 0.001-µ,E 50-WVDC,

metallized -filmC10-0.22-p,F, 250-WVDC,

metallized-tilm


MIC1-Electret microphone element(Radio Shack 270-090)

TI -125 -kHz matching transformer(Toko Coil, Digi-Key catalog#TK1901 or equivalent)

Printed -circuit materials, enclosure.IC sockets, polarized AC powerplug with line cord, wire, solder,hardware, etc.

PARTS LIST FOR THE BABY ALERT RECEIVER

SEMICONDUCTORSQ2, Q.1 2N3904 general-purpose

NPN silicon transistorQ3 -2N3906 general-purpose PNP

silicon transistorD5 -1N4004 I -amp, 400 -Ply. silicon

receifier diodeD6-1N4750A 27 -volt. 1 -watt Zener

diodeLED2-Light-emitting diode, 2 -volt,

20-mA

RESISTORS(All fixed resistors are 1/4 -watt. 5%

carbon units, unless otherwisenoted.)

R20 -3300 -ohm, 3 -watt, metal -oxideR2I, R29 -10,000 -ohmR22, R26, R28 -4700 -ohmR23 -470,000 -ohmR24 -100 -ohmR25 -1(X),000 -ohm

R27 -47,000 -ohm

CAPACITORSC11 --470-µF, 35-WVDC,

electrolyticC12-0.001-iLE 200-WVDC.

ceramic -discC13--0.001-RE 50-WVDC,

polyester -filmC14--0.001-ILF, 50-WVDC, ceramic -

discC15, C16 0.01-1.tE 50-WVDC,

ceramic -discC17 -2.2-µF, 10-WVDC, electrolytic


LI-1.5-tnH inductor (Toko Coil,Digi-Key catalog #TK3203 orequivalent)

BZI-Piezo buzzer (Radio Shack

273-065 or similar)Printed -circuit materials, enclosure,

polarized AC power plug with linecord, wire, solder, hardware. etc.

Note: The following parts areavailable from A. Caristi, 69 WhitePond Road, Waldwick, N.J. 07463:

Transmitter: printed -circuit board,$9.95; LM324 quad op -amp (L11),$2.50 each; LMC555CNoscillator/timer (U2 and U3),$2.50 each; TK1901 125 -kHzmatching transtOrmer (T1), $8.75each: MPSA42 high voltagetransistor (QI), $2.25 each; set of2 metal -film resistors. $1.25

Receiver: printed -circuit board, $9.95each: TK3203 1.5-mH inductor(L1), $7.75 each. Please add $3.00per order for postage and handling.New Jersey residents please addappropriate sales tax.

possible shock hazard. Low-pricedplastic enclosures are readily avail-able from electronics parts supplierssuch as Radio Shack. Using a 100%plastic enclosure eliminates the needto ground the chassis, so a 3 -conduc-tor power cord is not necessary. If youuse a 3 -conductor cord and housethe circuits in plastic enclosures, tapethe ground conductors of the cords sothat they cannot short to anythingelse.

On the other hand, if you choose tohouse either unit in a metallic or par-tially metallic enclosure (somethingthat is not recommended), it will benecessary to use a 3 -conductor linecord and tie the metal chassis, or themetal portion of the enclosure, to Ear-th ground.

Prepare the transmitter enclosureby drilling a series of very small holes

TO

117VAC

PL1

117V3

a

Fig. 7. Using an isolation transformer is the best way to test the circuit, and one mustbe part of the test setup when checking the project with an oscilloscope. You can usethis simple, low-cost setup to obtain line isolation.

T

in the enclosure to allow sound toreach the element. It will also be nec-essary to drill holes in both enclosuresfor the LED indicators. Also you have todrill holes in the receiver enclosure toallow sound from the piezo buzzer toescape; keep in mind that no metalpart or wire of the piezo element maybe left exposed. No power switch isrequired for either unit, since currentdraw is extremely low. However, youalways have the option of installingswitches if desired.

Transmitter Checkout. Electricalcheckout will require the use of a DVMor VOM; an oscilloscope may be nec-essary for troubleshooting if the circuitis non-functional due to improper as-sembly or one or more defectivecomponents. The transmitter must bechecked first. Once its operation is

12V

GROUND

SO1

(SEE TEXT)

3'l

117V

L

verified, it can be used to check thereceiver's operation. For the initial testremove the IC's from their sockets be-fore powering the circuit. Caution: Aswith any electronic project that is con-nected directly to the power line,using an isolation transformer is thebest way to test the circuit, and onemust be part of the test setup whenchecking the project with an os-cilloscope.

A simple, low-cost way to obtain lineisolation is to use two step-down trans-formers, with equal ratings, con-nected back-to-back (the two sec-ondaries connected to each other)as shown in Fig. 7. If line isolation is notused, use only a voltmeter for testing;connect the meter to the circuit be-fore plugging the transmitter line cordinto the AC receptacle. Do not touchany part of the circuit or meter withyour body when power is on. Voltagemeasurements are made with thenegative or common lead of the volt-meter connected to circuit ground(the negative side of C1), unless other-wise specified.

With all IC's removed from the trans-mitter board, apply power to the cir-cuit. The LED should light. Measure thevoltage across C1. The voltage acrossC1 should be about 80 volts DC. Mea-sure the voltage across C2, andacross C3; about 6.8 volts DC acrosseach capacitor is the reading you

should get. Measure the voltage atpin 10 of the U1 socket. Adjust R19 for areading of about 1 volt DC.

If you do not get the correct read-ings across the capacitors or at pin 10of U1, disconnect the line cord andtroubleshoot the circuit until the fault isfound and corrected. Check the ori-entation of D1 -D3, C1 -C3, and LED1.Use an ohmmeter to verify that eachblade of the line cord plug is con-nected to the proper part of the cir-cuit as illustrated in the schematicdiagram and the parts -placement di-agram. Measure the resistance acrossC1 -C3 to be sure that there is no shortcircuit on either the high -voltage busor regulated -voltage bus.

When power -supply operation hasbeen verified, and R19 has been set to1 volt, disconnect power from thetransmitter and insert the IC's into theirrespective sockets, being careful toobserve proper orientation. Be surethat none of the IC pins are inadver-tently bent under the body of thechip. Connect the voltmeter acrossC1. Apply power to the circuit andnote the meter reading; again itshould be about 80 volts.

Speak loudly into the microphoneand observe that the reading de-creases to about 40 volts as long asthe microphone picks up sound, thenreturns to 80 volts when the room issilent. Note that LED brightness de-creases significantly when the circuitis activated, as Q1 diverts current fromthe rest of the circuit. Failure to obtainthe above results indicates that U1 -U3or Q1 is not operating. Isolate the faultby first measuring the voltage at pin 7of U1, while speaking into the micro-phone. A normal indication is a volt-age exceeding 1 volt that responds tothe intensity of the sound.

If that measurement is normal,measure the voltage at pin 8 of U1. Anormal indication is about 12 voltswhen the circuit is dormant, andabout zero when speaking into themicrophone.

The operation of U2 can be verifiedby measuring the voltage at its outputterminal, pin 3. A normal indication iszero volts when the circuit is dormantand about 12 volts when activatedduring the 1 -second pulse time of theone-shot multivibrator. An os-cilloscope (with line isolation) may beused to verify that U3 is operational byexamining its output waveform at pin

3. A normal indication is a nearsquarewave of about 13 volts peak -to -peak when the circuit is activatedby sound. If U3 is normal, check pin 1 ofT1 for a 125 -kHz sinewave of about 1 or2 volts peak -to -peak. Both top andbottom slugs of T1 may be adjusted formaximum amplitude.

When the transmitter is operatingproperly, the upper and lower slugs ofT1 may be adjusted for maximum am-plitude of the 125 -kHz sinewave ap-pearing at pin 1 of T1. Use the properplastic tuning tool to avoid damageto the slugs. An oscilloscope is best forthat adjustment. A normal indication isa 2 -volt peak -to -peak sinewave.

When you are satisfied that the cir-cuit performs properly, R19 may beadjusted for more or less sensitivity asdesired, Use the LED as an indicator ofcircuit operation as sound reachesthe microphone. The circuit is mostsensitive when the voltage at pin 10 ofU1 is near zero. It is best to use only asmuch sensitivity as necessary to avoidfalse alarms.

Receiver Checkout. Be sure to ob-serve all safety precautions as de-scribed previously.

Connect a DC voltmeter acrossC10, and apply power to the receiver.The LED should light. Note the meterreading; a normal indication is about26 to 28 volts DC. If you do not get theproper reading, disconnect thepower and troubleshoot the circuit.Start by checking D5, D6, LED2, andC11 for correct orientation. Using anohmmeter or continuity checker, ver-ify that each blade of the line cord isconnected to the proper points.

When the power supply is opera-tional, plug the receiver's power corddirectly into a duplex AC receptacle.Plug the transmitter's power cord di-rectly into the other side of the samereceptacle. Speak into the micro-phone. The receiver should emit ahigh-pitched sound, indicating that ithas detected the 125 -kHz signal gen-erated by the transmitter. If possible,use a line isolation setup (like that inFig. 7) for the receiver and adjust L1'stuning slug to obtain the highest am-plitude 125 -kHz voltage at the collec-tor of Q3 as indicated by anoscilloscope.

Note the audio level that is requiredto operate the receiver. If more or lesssensitivity is desired, adjust R19 in the

transmitter accordingly. Remember,use only as much sensitivity as neces-sary to avoid false alarms. If the re-ceiver does not operate as de-scribed, check Q2, Q3, Q4, and theirassociated components. Check BZ1to be sure that it's connected to thecircuit with the correct polarity. Thebest way to troubleshoot the receiveris to power both receiver and trans-mitter through the same line -isolationtransformer and use an oscilloscopeto trace the 125 -kHz signal from C13/L1through Q3's collector.

With both transmitter and receiverplugged into the same duplex recep-tacle, the signal at the junction of C13and L1 should be about a 1 -volt peak -to -peak, 125 -kHz sinewave riding on arelatively small 60 -Hz waveform. AtQ2's collector the signal should beamplified to about 6 volts peak -to -peak as Q2 saturates.

The tuning slug of L1 should be ad-justed to obtain the maximum ampli-tude signal voltage at Q2's collector.That adjustment is best performed ifthe transmitter is relocated to a re-mote location to attenuate the RF sig-nal through the AC -line wiring. Whenso attenuated, the RF input to the re-ceiver at the junction of C13 and L1may be only about 0.1 volt peak -to -peak.

With an RF amplitude of severalvolts peak -to -peak at Q2's collector,the output of Q3 at its collector shouldrise to 15 volts or more as Q3 respondsto the drive signal from Q2. Finally, Q4should be driven into conduction,causing the piezo buzzer to operate.

Final Checkout. To check the rangeof the Baby Alert, connect the trans-mitter to an AC -power receptacle atits permanent location. Have an as-sistant stand by the transmitter tospeak into the microphone at yourdirection. Take the receiver to any re-mote location where there is an ACreceptacle. Apply power to the re-ceiver and have your assistant speak.The receiver should emit a tone.

That test can be performed at anyremote location where an AC recep-tacle can be found to verify that thesignal strength is sufficient to activatethe receiver. If desired, several re-ceivers can be assembled andplaced inside and even outside yourhome so that you'll never be totallyout of touch with your offspring..

Automate the operation of any light so it turns itself off and saves you money.

The price of electricity has goneup yet again! Have you everknown it to come down? And

yet we waste so much. Why, only theother day I went out to get the morn-ing paper, and the porch light was stillon. Must have been on all night. I start-ed thinking "Why can't my wife re-member to turn it off after . . . ." andthen I remembered / left the light on. Itwas then I decided to build a circuitthat would automatically turn off thelight. Before presenting the circuit, let'slook at some of the design criteria I

dealt with.

Designing the Circuit. Of course Iwanted a circuit that could be turnedon manually, but would turn off auto-matically. For that reason I decidedthe circuit should replace the existingporch -light switch, so it had to besmall enough to fit in a standard junc-tion box. It would also have to draw itspower from the existing wiring. Thatpresented me with a problem: Theswitch junction box in question was

BY DAVID PONTING

not wired with both the hot and neu-tral powerlines. It just had an incominghot wire and a switched hot wire go-ing to the lamp. So my circuit wouldhave to operate without benefit of theneutral line.

My solution was to place a resistor inseries with the switch, and place theautomatic control circuit in parallelwith the resistor. With the switch in the"on" position and a good bulb in theporch -light fixture to complete the cir-cuit, current flows through the resistor.The voltage drop produced acrossthe resistor by the current providespower for the control circuit.

However, I had to determine theoptimum value for the resistor: If it wastoo large it would make the porchlight dim, if it was too small the voltagedrop would not be sufficient to powerthe circuit. Furthermore, I had to de-termine if a resistor with sufficient wat-tage to handle the bulb's currentwould be physically small enough to

fit in the junction box, but run coolenough to prevent damaging theother components.

The first task was to determine thecurrent flow through the bulb. To fig-ure that I assumed I'd be working withat most a 100-wcrt bulb operating offa 120 -volt supply. The current wouldequal the wattage divided by thevoltage, which comes out to 0.83amp. Now I needed to find the valueof resistance that will yield a voltagedrop sufficient enough to power thecontrol circuit. Taking a guess that I

needed about 12 volts and dividingthat by 0.83 amps yielded a resis-tance value of about 15 ohms. Now Iturned my attention to figuring out thewattage of the resistor. Multiplying thevoltage drop times the current indi-cated I'd need a 10 -watt resistor-asuitable size. The resistor would gener-ate some heat, but since it would onlybe on for a couple of minutes at atime, it would not harm the other com-ponents in the junction box.

An additional concern of mine was

if the resistor value would still be suit-able when operating with a smallerwattage bulb, say 40 watts. Let's gothrough the math again to see. Thewattage over the voltage equals thecurrent, so if we divide 40 by 120, weget 0.333 amp. Now, what voltage willbe dropped by the 15 -ohm resistorwhen it carries 0.333 -amps? Multiply-ing resistance times current, the an-swer is 5 volts-still a usable value. Ofcourse, at the reduced current levelthe resistor's 10 -watt rating is morethan sufficient.

Just to check out these theoreticalfigures, I ran a series of tests usingmock circuits. To summarize the testresults, I discovered that 40 -watt bulbsare not made with the same degreeof accuracy as the larger wattagebulbs. However, the circuit should workjust fine regardless of that variance.

The rather lengthy activation time(2 minutes) presented me with an-other hurdle to overcome. Two min-utes is pretty long in electronic terms.A resistor/capacitor-based timing cir-cuit would require a large, leaky ca-pacitor. The capacitor would waste alittle energy and may be too large tofit easily and safely into a standardjunction box. Obviously an RC circuitwouldn't do. Let's take a look at theactual circuit to see how I avoidedusing such a timing scheme.

The Control Circuit. The AutomaticPorch -Light Control circuit is shown inFig. 1. The hot lead in the switch box isconnected to one side of the push-button switch, S1. The switch runs to R1,the 15 -ohm, 10 -watt resistor that isconnected to the bulb via the housewiring. When the pushbutton ispressed it completes the circuit light-ing the bulb. The small voltage drop

O across R1 is full -wave rectified by theO bridge, BR1, and the pulsating DC out< of the bridge is smoothed by C1 andco limited to 6.2 volts by the Zener diode,cn Dl. That voltage acts as the supply forco" U1, a CMOS 4020 counter/divider.

0co That IC has two inputs, a clock input

(pin 10) and a master -reset input (pino 11). Let's consider the master -reset in -

0 put first. Counting only occurs whenthe master reset is low. When the mas-t ter reset is high, the counter is reset to

d zero, its outputs go high, and it will notcount. However, to ensure that thecounter starts at zero it is necessary to

64 reset the counter with a positive pulse.

TOHOT

LINE

R1

15f210W

0 0-.--'MTR1

400 -VOLT

4 -AMP

R2

27004

U2M0C3041

it,BR11A

100V

C1

1000

HOT TOBULB

R3

10MEG

16

10

D1

6.2V5W

U1

4020

C2-12- R62200

11

R55.6K

R4100K

012N2222

*SEE TEXT

Fig. I. The Automatic Porch -Light Control Circuit holds a Triac on until a 4020divider counts a number of 60 -Hz powerline pulses.

That pulse is produced by C2 andR4. Before the pushbutton is pressedthere is no voltage across C2 so it is

fully discharged and the master -resetpin is low. When the pushbutton ispressed, C2 pulls the master -reset pinhigh as it begins to charge. That resetsthe counter. Once C2 is mostlycharged there isn't much current flowthrough R4, so the resistor pulls themaster -reset pin low. At this point thecounter/divider begins to count.

What the counter/divider countsare the clock pulses into pin 10. Thesepulses are derived straight from theswitched side of the hot line, which, asyou know, operates at 60 Hz. The cur-rent flow into pin 10 is strongly attenu-ated by the 10-megohm resistor, R3.

The counter/divider contains anumber of different stages con-nected one after another and eachstage divides the pulses it receives byIwo. So the first stage divides the 60 -Hzsignal to produce a 30 -Hz square -wave. That signal is divided to pro-duce a 15 -Hz squarewave, and so on.The output of a number of thesestages are available via pins on the ICpackage. The control circuit uses theoutput at pin 3. The signal at that out-put has a period of about 1361/2seconds (i.e. a little bit over 2 minutes16 seconds).

If you think that leaves the light onfor too long, then use the output frompin 2, its period is half that of pin 3.Similarly, the output of pin 1, is half thatof pin 2.

Getting back to the circuit, whenthe counter/divider is counting it theoutput pin is low, which holds Q1 off.The LED in the optocoupler receivescurrent from R6, so the optocoupler

PARTS LIST FOR THEAUTOMATIC PORCH -LIGHT

CONTROL

RESISTORS(All resistors are 1/4 -watt, 5% units

unless otherwise noted.)RI-IS-ohm. 10 -wattR2 -270 -ohmR3-I0-megohmR4 -100.000 -ohmR5 -5600 -ohmR6 -220 -ohm

SEMICONDUCTORSU1-4020 14 -stage ripple counter,

integrated circuitU2-MOC3041 optocoupler,

integrated circuitQ1 -2N2222 NPN transistorTRI-4-amp, 400 -Ply, Triac

(isolated tab)BRI-1-amp, 100 -Ply, bridge

rectifierD1 -6.2 -volt, 5 -watt, Zener diode


10-WVDC, electrolytic50-WVDC, electrolytic

SI-Pushbutton switch (Radio Shack275-609)

One I6 -pin, and one modified 8 -pinIC socket (see text), 8-32hardware, switch -box fixingbracket (see text), blank switch -box panel, wire, solder, etc.

activates the Triac, TR1, completingthe circuit to the bulb so it remains litwhen S1 is released. When the timeperiod passes and pin 3 goes high,transistor Q1 switches fully on so its col-lector is grounded. That shorts the op-

tocoupler's LED, turning off the Triacand extinguishing the light.

Safety Tips. Before we get to theconstruction details a word or two ofcaution is in order. When building thecircuit keep in mind that when thecircuit is active both AC legs of thecircuit are hot. That is, of course, nodifferent from the switch inside anyswitch -box in the house: hot is alwayspresent on one side of the switch, andappears on the other side when theswitch is closed. Nevertheless, whentesting this circuit board, the utmostcare must be exercised to see thatno part of the board is touched.Once the device is in its switch -box, it isno more dangerous than the stan-dard switch it replaces, but until thenhandle it with caution.

On a different note, when you lookaround for a Triac try to get one withan isolated tab. That will prevent thetab from shorting the AC powerlineshould it come in contact with one ofthem. Also make sure the pushbuttonswitch you use can handle powerlinevoltages at currents up to about 1amp. The switch recommended in theParts List has not only a more thanadequate rating for the circuit, but italso has an ideal length, allowing allthe fitted components on the PCB tobe clear of the switch's mountingbracket (which we'll discuss in a mo-ment).

Preliminaries. Although very cau-tious point-to-point wiring will work, Irecommend that you build your Auto -

o

17/ut INCHES1

Fig. 2. Using this foil pattern to make aPC board is recommended. It willvirtually eliminate the possibility ofwiring errors.

-R2 -

TR1

10 BULB TO HOT

Fig. 3. Stuff the board as shown here. Note that the switch and nuts are mounted onthe foil side of the board.

matic Porch -Light Control on aprinted -circuit board made from thefoil pattern shown in Fig. 2. Rememberthat if you want a different delay time,alter the foil pattern or circuit board toaccommodate the delay you want asoutlined earlier.

Some special steps must be takenfor drilling the circuit board. For exam-ple, the flat terminals on the pushbut-ton switch have to be soldered to thePCB, so narrow slots have to be madein the board to accept them (see Fig.3 for their position). These are bestachieved by drilling a standard PCBsize hole (about 1 mm), drilling twomore holes adjacent to the first, andjoining them together by carefully fil-ing with a small needle file.

Also be sure to make two holes inthe board large enough to accom-modate 8-32 bolts. These holes shouldbe located on the board where theterminal connections for the hot andbulb wires are to be made. Once theboard is drilled, pass an 8-32 screwthrough each hole from the compo-nent side and fasten them withmatching nuts. Solder the nuts to thefoil being careful not to bind thescrews to the nuts. Remove the screwsfor now, and the circuit board is ready.

Prior to stuffing the board you willneed to modify some of the parts, solet's discuss that now. Do not solderanything to the circuit board until youare told to do so.

The body of the switch has to passthrough a bracket that will hold it (andtherefore the PCB) to the junction box.

You can take the retaining bracketfrom a plain wall switch, either a newone or the one you're replacing. If youwant to use the bracket from theswitch you're replacing, there aresome instructions for safely removingthe switch from the junction box givenlater (see the section entitled "Testingthe Unit"). Once you have the switch,remove the bracket by carefully drill-ing out the rivets that hold it in place.

The pushbutton switch can now bepassed through the central hole ofthe bracket (where the lever of theremoved switch was). It may need asmall rectangular piece of aluminumas a washer to hold it in the middle ofthe hole. Now finger -tighten theswitch in position with its own washerand nut. When fixed in this way, theswitch should be rotated so that its twocontacts run parallel to the bracket'slonger dimension. Hence, when thePCB is finally soldered to the switch,the board will have its longer dimen-sion parallel to the bracket as well.Now securely tighten the switch to thebracket.

Drill a hole in the center of the blankswitch box panel so that the button onthe switch can come through. Theswitch recommended in the Parts Listhas a removable button, so you onlyhave to drill a hole large enough toaccommodate the shaft of the switch.Later, when the switch and switch boxpanel are in place, you just have topop the button back on the shaft ofthe switch and it will hide the hole.


Gain on the CheapNothing can give your ham rig

better bang per buck or labor than a good antenna.

Antenna design is a perennialtopic for radio buffs. Whetheryou are a shortwave listener,

amateur -radio operator, scannermonitor, or a citizen's bander, the an-tenna is probably the most importantaspect of your set-up. While a greatdeal can be done to improve re-ceivers, transceivers, and transmitters,for the radio buff's dollar there isnothing that will produce as muchbenefit per nickel as a good antennasystem. And the antenna need not beterribly expensive. While a multi -kilo -buck rotatable beam antenna is cer-tainly a wonderful thing to have, notall of us can afford such an antennaor have the space to put one up. Insome areas, a really nice commercialantenna isn't even legal because oflocal zoning regulations, etc.

Fortunately, wire antennas can bebuilt for less than commercial anten-nas. They can be installed in areaswhere a tower cannot, or where one

BY JOSEPH J. CARR, K4IPV

would be prohibitively expensive to in-stall A wire antenna is also well worthconsidering because it provides con-venience and low cost, and some de-signs can provide a surprising degreeof gain and directivity.

Gain and Directivity. Gain and di-rectivity are the two interrelated as-pects of antenna design that make agood antenna so important to a ra-dio system. These two concepts areessentially the same because anten-nas obtain "gain" by focusing the RFenergy into limited directions ratherthan all directions. Gain is measuredby comparing the strength of a signalradiated by an antenna in each di-rection to the signal strength thatwould be produced by an ideal iso-tropic radiator (i.e., a uniform sphere).The signal produced by such an idealantenna could be viewed as an ever-expanding series of spheres with theantenna at the center (something like

the layers of an onion). The larger asphere's radius, the greater its surfacearea. Since all the spheres shouldhave the same amount of RF energybut different surface areas, signalstrength is measured in milliwatts persquare centimeter (mW/cm2).

A directional antenna focuses all ofits energy into a limited direction, somore energy is found in each unit ofarea along that direction. In otherwords, the signal strength in mW/cm2increases along that direction. Be-cause of its inherent directivity, suchan antenna provides the following: Increased received signal strengthfrom distant transmitters (i.e., makes areceived signal louder).

Freedom from strong interferingsignals from directions not the sameas the signal of interest.

Increased transmitted signalstrength at distant locations (i,e,,makes your signal louder). The Law of Reciprocity makes the

antenna perform during reception asit does on transmission, so the samedesign can benefit both types of user.

The first two items on the list benefitall users of radio equipment, while thefinal one helps CB'ers and hams. Thefirst benefit (i.e., making distant signalsstronger) is probably not the advan-tage it seems at first blush except to asmall percentage of radio amateurs.Increasing the received strength of"Radio Zlotplatz" is only of marginalbenefit if it is already audible at yourlocation and your receiver has bothan automatic gain control and rea-sonable selectivity. The gain is of use,however, when attempting to listen tostations that are so weak that they arenear the noise threshold. Increasingantenna gain may well bring such astation up enough to hear audiblywithout also increasing the overallnoise as much as would a pre-amplifier.

So what use is a gain antenna if arandom length of wire tied to a con-venient tree will give us a strongenough signal? Recall that gain anddirectivity are merely restatements ofthe same thing. The selectivity of yourreceiver will help eliminate adjacentchannel interference. You can narrowthe passband down, use "single sig-nal" techniques (where appropriate)and otherwise shunt unwanted adja-cent channel signals off to oblivion.

Co -channel interference is a dif-ferent matter. If the offending signal ison the same channel, then the re-ceiver will "hop around" trying to elim-inate it. But, if the offending signal iscoming from a different directionthan the desired signal, it is possible toplace the low -gain "null" of the direc-tive antenna in that direction, Thus,the offending signal is attenuated bythe antenna's directionality.

The trick of using an antenna to se-lect signals is well known to those whouse rotatable antennas. What is per-haps a less popular fact is that youcan derive the same benefit from ajudiciously placed fixed antenna. Forexample, an "east coaster" mightwant to aim an antenna so that itpicks up shortwave transmissions fromAfrica, South America, Europe, orOceana, while at the same time elim-inating signals from other regions (youmight be surprised by what's buriedunderneath the North American Ser-vice of Radio Moscow). The null could

900011®

L2

1:1 BALUNL2 = L1/2 TRANSFORMER

L1 = 468/fmt4z

L1

A

L2

MAXIMA

7552 COAX

VAC

B

Fig. I. In "A" is a simple half -wavelength dipole antenna. Ideally it should produce aradiation pattern like the one shown in "B."

be placed in the direction of the of-fending signal (or cacophony of sig-nals), even though the main lobe (i.e.,direction of maximum gain) is not di-rectly on the area of interest.

The phenomenon is not limited toshortwave listeners and hams. In-deed, scanner users and FM -bandDX'ers may have even greater needfor directivity and gain. If you are farremoved from a station, then the gainfeature of an antenna may be attrac-tive to you as well. Or, if you want tolisten to a distant station on the samechannel as a stronger, nearby station,then directivity may be just what youneed. A friend of mine used to listen toa bluegrass music station 90 milesaway with usable, if noisy, reception ...until another station occupied thesame channel closer in. Fortunately,the new station was about 40 milesdistant in a different direction, so again antenna with a good directivitydid the trick. Before we discuss thevarious antennas you can use to im-

prove your own set-up, another topicdeserves attention: Safety!

Rules to Follow. Erecting antennascan be a dangerous affair. Every yearthe radio community is saddened bystories of people who were killed orseriously injured in the act of erectingantennas. The most serious threatcomes from foolishly attempting toerect a wire antenna by tossing it overAC power lines. While it may betempting to do so, especially whenthe most convenient support struc-tures are on opposite sides of thepower line, this feat must never beattempted! The argument that bothantenna and power wires are insu-lated does not help, for insulation canand does deteriorate and falls apartwith remarkably little force. It is neversafe to do that trick, so don't.

Also, keep in mind where the anten-na will go if it breaks. Look around theyard and determine whether or not itwill be capable of "wind -whipping" 67

'000

a

AdbiPROPAGATION

DIRECTOR

ii ,00000

DRIVEN

ELEMENT

REFLECTORSC

0041Q

A

MAXIMA

ANTENNA

B

Fig. 2. You can improve the performance of a dipole by adding director and reflectorelements that force the RF energy to move in a given direction.

into a power line, or if it will become ahazard on a path or sidewalk, or if it

will crash into a window or vehicle(insulators and baluns will break glasswhen wind whipped).

Use properly designed insulators,not ad hoc substitutes, for the end andcenter insulators. The rope should besufficiently strong to hold the antennaunder all wind conditions, and shouldbe tied to a spring or counterweightto permit some give. Use good qualityNo. 12- or No. 14 -gauge wire. Copper -weld is a steel core, copper -clad wireintended for this purpose.

Finally, when erecting the antenna,especially if standing on a ladder, beaware of where the wire is at all times.It can easily become entangled inyour feet or ladder support, andcause a serious fall. Always work withanother person so that help is near athand; young readers should work witha knowledgeable adult until they arealso experienced in the antenna -erection process. Wire antennasseem very easy to erect alone, butthat's a fool's game from a safety per-spective. With these important pointscovered, lets get to those antennas.

The Half -Wavelength Dipole An-tenna. Although disdained by thetechnically sophisticated (withoutgood reason), and despised byowners of super -arrays, the "lowly" di-pole (Fig. 1) is the least expensive andmost common form of directionalwire antenna. It is a horizontal half -wavelength radiator fed at its center.Although the feedpoint impedancevaries with height above ground, thedipole usually makes a good imped-ance match for 75 -ohm coaxial ca-ble. The overall length of the antenna(L1) can approximately be found byusing the equation in Fig. 1 where L1 isin feet, and f is the frequency of inter-est is in megahertz. The length is onlyapproximate because local condi-tions can conspire to alter the elec-trical length a bit, so some tuning mustbe done on any antenna once it is

erected. The length of each element(L2) is about one-half of L1 as shown.

The ends of the dipole are sup-ported by end insulators and lengthsof rope. The rope can be attached totrees, masts, buildings, or other struc-tures. The feedpoint of the dipole canbe constructed with another end in-sulator such that the center conduc-tor of the coaxial cable is connectedto one L2 radiator element, while theshield is connected to the other radi-ator. A better result, and a more con-sistent pattern, will result if the coaxialcable is connected to the antennathrough a 1:1 balun (which stands forbalanced -unbalanced) transformer.They are readily available from radio -supply outlets, or can be homemadefrom toroidal transformer cores follow-ing instructions given in various texts(see the boxed copy entitled "For Fur-ther Reading" appearing with this arti-cle).

Figure 1B shows the radiation pat-tern for the dipole antenna. This view isfrom above. Note that the pattern is afigure eight with the main -lobe max-imas perpendicular to the radiator el-ement. The minima, or nulls, are thedirections of minimum gain and are inline with the radiator element. In otherwords, if you want to null a station tothe west or east, and receive along anorth -to -south line, then run the an-tenna east to west. The antenna pat-tern in both the horizontal and verticaldirections is best for most applicationswhen the antenna is at least one half -wavelength from the ground, and is

--- 10060

L1 L1

®Oth

L1 = 600/f

L2 = 103/f

Fig. 3. The double -extended Zepp antenna is similar to a plain dipole, but it has asnatching section and a balun at its feed point.

PHASE -

REVERSALSTUB

4:1BALUN

L1

PHASE -

REVERSALSTUB

Fig. 4. The collinear Franklin -array antenna, shown here, can be extended to containany number of elements. The number is only limited by the weight your rope canhandle.

L1

UP

GROUND

00114R

L2

L1

L1

L3B.

Fig. 5. The lazy -H antenna consists of two dipoles pointed in opposite directions. Thefeed points for the antenna (points A and 131 need to be determined by experiment.

3900

®000e

preferably several wavelengthsabove ground (which is nearly impos-sible on lower frequencies),

The dipole is the easiest directionalantenna to build and use, and it is alsothe most well behaved when it comesto tuning. It has a gain of approxi-mately 1.7 decibels (dB) above theideal isotropic radiator mentionedabove.

Wire Yagi Beam Antenna. The Yagi

L1TEET = 478/fmH,

L2FEET = 492/fmm,

L3FEET = 246/fmH,

antenna is a directional beam anten-na that is made from dipole eleMents(see Fig. 2A). Most of the large rotata-ble antennas used on shortwave andVHF bands are basically tubing -basedversions of the Yogi concept. The pat-tern for the Yogi beam antenna ismonodirectional, as shown in Fig. 2B.This pattern is, incidentally, idealizedand doesn't show sidelobes andbacklobes that represent wasted en-ergy but hopefully those are kept low

enough to not be a problem. Thebeamwidth of the antenna is the an-gle between points "A" and "B" wherethe gain falls off -3 dB from the gainat the maxima.

It is possible to make a fixed Yagibeam antenna from wire and in-sulators, as shown in Fig. 2A The drivenelement is a half -wavelength dipolesimilar to the one in Fig. 1A; its approxi-mate length (before tuning) is foundfrom the equation for L1 presentedearlier. The driven element can be fedeither directly as shown, or through a1:1 balun transformer to 52 -ohm (not75 -ohm) coaxial cable. The elementin the direction of maximum radiationis called a director, and is about 4%shorter than the driven element, Sim-ilarly, a reflector is behind the drivenelement and is about 4% longer thanthe driven element. Although the an-tenna in Fig. 2A has one director andone reflector, it is possible to use anynumber of reflectors and directors(and each one narrows the beam -width and therefore increases thegain of the antenna.

The spacing (S) between elementscan vary from approximately 0,15wavelength to 0.25 wavelength, or0.3L1 to 0.5L1 to use the half -wave-length element lengths as a frame ofreference (many builders try to makethe spacing 0.2 wavelengths). Thespacing is difficult to maintain, es-pecially as the wind blows . , but it isnot strictly necessary to always havethe spacing exact.

Double -Extended Zepp Antenna.The double -extended Zepp antenna,shown in Fig. 3, provides a gain ofabout 2 dB at right angles to the an-tenna wire plane. It consists of twosections of wire, each one of a lengthbased on the desired frequency ofuse as shown in the figure.

The D.E. Zepp antenna can be feddirectly with 450 -ohm twin -lead(available from Wire Antenna Sup-plies Radio Works, P.O. Box 6159,Portsmouth, VA, 23703), especially if abalanced antenna tuner is availableat the receiver or transmitter end. Al-ternatively, it can be fed from amatching section of twin lead (or par-allel line) as shown if coax is preferred.Use the equation shown in the figureto determine the length of the match-ing section (L2).


HOLIDAY LIGHT TE,STE1BY JOHN YACONO AND MARC SPIWAK

Christmas should be a time for peace and joy-not forwrestling with lights that don't light!

Many of you are probably fa-miliar with what's involved infinding one burned -out light

bulb in a long string of them. It's reallyfrustrating when you have to pull eachbulb and replace it with a known -good one, just to find the one badone. And if you're lucky, you'll find thebad bulb and the string will come tolife. If you're not lucky, there's a break inthe wire somewhere in the loop, andyou won'tfind it by checking the bulbs.

If you've ever had that problem, or ifyou regularly repair anything withmany lights wired in series, then you'llcertainly appreciate this neat littlegadget: the Christmas -Tree Light Test-er. It points you in the direction of thebad bulb by plugging into any socketin the string and seeing which of twoLED's light up. Which LED lights de-pends on the direction from whichpower is being supplied to the LED's.Should you get to a point where theLED's indicate a change in direction

then you know there's a break in thewire or a bad bulb somewhere be-tween the two sockets just checkedand you also know exactly where. Thetester also comes in handy for testingstrings of lights on vanity mirrors, stageprops, and so on. Let's take a look atthe circuitry that lets us do this.

A 555 Circuit. The tester circuit isbased on a 555 oscillator/timer. How-ever, the IC is used in a non-standardconfiguration, so let's consider how a555 timer works in a more commoncircuit before seeing how it's used inour tester.

A 555 wired for astable operation isshown in Fig. 1. If you apply power tothe circuit, capacitor C starts tocharge through RA and RE,' and theoutput is high. The FET in the 555 caninitially be ignored as it is off. The rateof charge is thus determined by thevalues of RA, RB, C, and V00.

The resistor network composed of

R;, -R13 divides the supply voltage(Vcc) into 1/3 V00 and 2/3V00 (calledthe "trigger" and "threshold" voltages,respectively). Note that both com-parators (Oland C2) monitor the volt-age stored in the capacitor. Com-parator C1 compares the capacitorvoltage to the threshold voltage andC2 compares it to the trigger voltage.

When the capacitor charges to thethreshold voltage, C1 momentarilygoes high, toggling the flip-flop. Thatcauses the internal FET to start drain-ing the charge off the capacitor via RB(without any of the discharge currentflowing through RA), and the outputterminal goes low. The rate of dis-charge is thus determined by RB, C,and V00 (but not RA). Once the ca-pacitor voltage drops to the triggervoltage, C2 is triggered and togglesthe flip-flop. The FET then turns off, theoutput goes high, and the capacitorbegins to charge again.

There are a few interesting facts

A

VCC VCC VCON0

3

CONTROL

THRESHOLD

TRIGGER

GND

VA

RESET

6R1

FLIP-1

FLOP

S

1

o OUT

DISCHARG

-J

Fig. I. A 555 oscillator/timer wired for astable operation. Capacitor C chargesthrough RA and R8. The rate of charge is thus determined by the values of RA, Rn, C,and

about that process. First, the time thatit takes for the capacitor to chargefrom 1/3Vcc to 2/3Vcc, which is the timethe output remains high, is given by:

th = 0.693(RA + ROC

The time it takes for the capacitor todischarge from 2/3Vcc to 1/3\/cc, whichis also the length of time the output islow, is given by:

t = 0.693(RB)C

Note the absence of RA in the lastequation. That's because only RB is inthe discharge path. That prevents usfrom attaining a 50% duty cycle (thcan't equal t1). Some may proposedoing away with RA, but that wouldshort the power supply through thedischarge pin at the beginning of thedischarge cycle. However, there is an-other method for obtaining a 50%duty cycle-by putting a diode point-ing down (cathode toward the ca-pacitor) in parallel with RB, and settingRA equal to RB. In that way, RB is by-passed during charging, but it is still inthe discharge path. That technique isused in our circuit, as you'll see in aminute.

The Tester. In the tester (shown in Fig.2), a battery (B1) is the power supplyfor the circuit. The 555 oscillator/timeris connected to R1, R2, and C1 so thatit produces a train of pulses at its out-put (pin 3), however its operation hasbeen modified by the addition of D1as described earlier. The reason forthat will become clear as we pro-ceed. The highs and lows produced

R4

i680i2R1

120K7

R2

120K

w D1-1N914

6

LED3 C1

.1

2

14 18

LED2 will not light, indicating a prob-lem in that part of the circuit.

Effectively, since a darkened LED in-dicates the troubled side of the circuit,by placing the probe in the middle ofa faulty "sub -string" of lights, you im-mediately cut the number of suspectbulbs in half. You can repeat that pro-cess to cut the remaining number inhalf, again by re -installing the dislo-cated bulb and moving the probe toa socket mid -way between the pre-vious location and the end of thestring in the direction of the fault. Byrepeatedly cutting the number of sus-pect bulbs in half (by moving to thecenter of the troubled area over andover), you will eventually dislocate thebad bulb, which will cause both LED'sin the probe to light.

RESET Vcc

DISCHARGE OUTU1

555THRESHOLD

TRIGGER CONTROL

GND

R3

34700

5

LED2

C2.01

PROBECONTACTS

0Si

4-

B1

LED1 9V

SO1 1'

Fig. 2. The 555 oscillator/timer produces a train of pulses at its output, which arepresented to LEDI and LED2 via R3.

by the 555 are applied to LEDI andLED2 via R3. The two LED's have beeninstalled in the base of a Christmasbulb (in place of the incandescentbulb) so that the free end of each LEDreplaces one of the evicted bulb'scontacts.

To help explain how the circuit isused, imagine that the AC plug for astring of lights has been inserted inSO1 and one of the bulbs in the string(let's say the center -most one) hasbeen replaced by the probe so thatLEDI is touching the ground side of thebulb's socket and LED2 is touching thepositive side of the socket.

With such a setup in mind, if all thebulbs in the string of lights are good,both LED's will light-LEDI will lightwhen U1's output goes high and LED2will light when U1's output goes low.However, if any bulb in the path be-tween LEDI and ground is bad (open),LEDI will not light, indicating that thefaulty bulb lies in that side of the cir-cuit. On the other hand, if any bulb inthe path between LED2 and thepositive side of the battery is bad,

Based on some simple math, thestrategy provides quite a time savings.Take for example a string of only twen-ty bulbs. Instead of replacing all twen-ty bulbs one at a time, you need onlyperform (at worst) four tests and with-out exposure to lethal AC power! Withlarger strands, the tester gives youeven more of an edge.

Some of you may be wonderingwhy we chose to use a 555 oscillator/timer, instead of two separate currentloops under direct power. The reasonis to conserve battery life. The string oflights will quickly gobble -up batterypower during normal testing. By usingthe 555, the battery is only connectedto the good section of bulbs 50% ofthe time until you displace the de-funct bulb. All in all, that about dou-bles battery life.

The reason for designing the circuitfor 50% operation, as opposed tosome other duty cycle, is to ensurethat both LED's will have equal time tolight. That is very important when theprobe is placed so that there are alarge number of bulbs in the path of

R3

PROJECTCASE

HEAT -SHRINKTUBING

UNUSEDENDS

PERFBOARD

Fig. 3. The probe is made from a T-shaped piece of perfboard. One lead from eachLED replaces the original bulb leads in the bulb base.

just one of the LED's: Since that LED willglow dimly due to the total resistivedrop of the bulbs, it should be lit a fairamount of time to make its glow no-ticeable.

Helpful Tips. There are a couple ofpractices that will make troubleshoot-ing even easier. First of all, most Christ-mas -light strings contain severalseparatein parallel. To ease troubleshooting,you should mark all of the bulbs in thefaulty serial circuit so that you canconcentrate on them alone. The bestway to do that is to plug the string intoan AC source and mark the base ofeach darkened bulb; remember,however, that you're fooling with AC(albeit it for a short time and with theprotection of insulation).

Second, if neither LED in the probelights in the course of testing, chancesare you've installed the probe back-wards (with LEDI connected to thepositive side of the battery and LED2connected to ground). If so, pull theprobe out, flip it around, and reinstallit. If that doesn't work, there's morethan one out -to -lunch bulb, and youhave placed the probe between thetwo bad bulbs. You can find the firstbad bulb by working your way towardit (half a suspect area at a time). Forexample, say you next test a pointhalf -way between the completelypowerless socket and the wall plug. Ifone of the LED's lights, you've passedone of the bad bulbs. You then backup to a socket half -way between theone you're in and the one that pro-vided no illumination.

PARTS LIST FOR THECHRISTMAS -LIGHT TESTER

SEMICONDUCTORSU1-555 oscillator. timer. integrated

circuitLEDI, LED2. LED3-Light-emitting

diodeDI-IN914 small -signal general-

purpose silicon diode


C1- 0.I -µF ceramic -disc capacitorC2-O.01-µF ceramic -disc capacitorRI, R2-I20,000-ohm, 1/4 -watt, 5%

resistorR3 -470 -ohm, 1/4 -watt. 5% resistorR I 680 -ohm, 1/4 -watt, 5% resistorSOI----Single AC socketSI-SPST switchBI -9 -volt transistor -radio battery.Perfboard material, Christmas bulb

base, heat -shrink tubing, projectbox, wall -socket faceplate, batteryclip, double -sided foam, stand-offs, wire, solder, hardware, etc.

However, if both LED's are still dark,even though the probe is insertedwith the right polarity, then youhaven't moved far enough (you arestill between the bad bulbs). Once thefirst corrupt bulb is found, use the nor-mal procedure to find the secondbulb.

Getting It Together. Because therearen't very many parts required forthe tester, we decided to build thecircuit on a piece of perfboard usingpoint-to-point wiring. For very compli-cated circuitry, it might pay to spend

the time making a PC board, but forsimple circuits, its quicker to do it thisway. And the light -tester circuit truly issimple-there are only seven partsmounted on the board. Wherever apoint on the board must be con-nected to something off the board,we installed a 6 -inch length of wire tobe trimmed to length later on.

We mounted all of the parts, exceptS1, LEDI-LED3, and R4 on the per-fboard. The power -on indicator (LED3)was mounted on the lid of the projectcase, and its current -limiting resistor(R4) was wired in series with it. SwitchS1, and the AC socket (501), were alsomounted on the lid.

In order to be able to plug into astring of lights, we used the plasticbase of a spare Christmas light bulb tomake a "probe." Normally, a bulb isinserted into the base, and its leadsprotrude from two holes at the bot-tom. The bulb's leads are bent uparound the sides of the base to hold itin place. To remove the bulb from thebase, simply bend the leads outstraight and pull out the bulb.

To make the probe, we used a T-shaped piece of perfboard andmounted the direction -indicators(LEDI and LED2) on it. Figure 3 showsthe probe's details. One lead fromeach LED (the cathode of LEDI andthe anode of LED2) replaces the origi-nal bulb leads. The leads are bent outof the end of the bulb base in thesame way as the original bulb leads.The other two LED leads are twistedtogether and soldered to the wire thatconnects the probe to the light -testercircuit board. (Actually ifs soldered toone end of R3, which is mounted onthe board.)

As you can see from Fig. 3, we usedtwo conductor wire for the probelead, even though only one conduc-tor is needed. The reason we did thatis to secure the probe onto the wiremore securely. Although shrink-wraptubing holds the probe together, it'sactually two pieces of double -sidedtape or foam that secure the probe tothe wire.

A simple circuit demands a simplecase. There are no particular require-ments, so use whatever case youhave on hand. The circuit board ismounted on the bottom of the caseusing a couple of spacers and screws,and the 9 -volt battery is held in placewith a piece of double -sided tape.

We often take for granted thatour identity can be verifiedby our voice. How many

times do we receive phone calls, andjust by the sound of the persons voiceknow who it is without having the per-son identify themselves. Wouldn't it befun if we could change our voice fromtime to time? Well, with the Voice Dis-guiserdescr bed in this article, it is pos-sible to electronically change thesound of your voice to the extent it cannot be recognized.

Have loads of funfooling friends andfamily when theycall with this simplefrequency -shiftingcircuit

The Voice Disguiser does not muffleor filter your voice, instead it actuallyshifts the frequency spectrum of yourvoice higher or lower. The Voice Dis-guiser is designed to be used over atelephone or a public address system,however, it can also be used by itself.To couple the altered voice to thephone line, the telephone receiver isplaced near the Disguiser's speaker.

You can use the Voice Disguiser tohold confidential conversations with-out revealing the identity of the par-ticipants or to play tricks on yourtiends. You can also use it to answeryour phone when you don't want toreveal your identity.

General Description. Figure 1 showsa block diagram of the Voice Dis-cuiser The circuit is comprised of amicrophone, audio amp, two os-allators (one fixed at 4 kHz and theother variable up to the same fre-quency), two 5 -kHz low-pass filters, twomodulators, an output amp, and aspeaker,

The microphone picks up yourvoice (converting it into an electricalsignal) and feeds it to the audio am-plifier, which boosts the input to a usa-ble level. From there, the signal isoutput to the first modulator, where it isfrequency modulated with the outputof the first 4 -kHz oscillator. The signal isthen fed through the first low-pass fil-

ter, which passes signal frequencies of5 kHz or less, stripping the high-tre-quency components from the modu-lated signal.

From there the signal is fed to thesecond modulator, where the modu-lated, low-pass filtered signal is fre-quency modulated with the output ofthe variable 4 -kHz oscillator. The out-put of that modulator is then fedthrough the second low-pass filter(with the same results as produced bythe first) to the audio -output amplifier,where its power is boosted and sent tothe speaker.

Getting into Details. A completeschematic diagram of the Voice Dis-guiser, which is a lot less complicatedthan it might appear, is shown in Fig. 2.Microphone MIC1 picks up the voicesignal and feeds it to an audio ampli-fier, consisting Q1 and Q2, and a fewsupport components. The amplifierhas a low-pass gain response that lim-its the voice frequencies to 5 kHz orlower.

The voice signal is then fed to theinput of the first balanced modulator,which is comprised of U1 -a, U1 -b, U2 -a,

BY VINCENT VOLLONO

ana U3 -a. The output of the first 4 -kHzoscillator, built around U3 -f and U3 -e,is fed to the carrier input of the firstmodulator. The frequency of the firstoscillator is controlled by the setting ofpotentiometer R13. The modulatoroutput-_a double-sideband sup-pressed -carrier signal centered on 4kHz-is then filtered by the first 5 -kHzlow-pass filter, formed by U2 -b, whicheliminates the upper-sideband sig-nals.

Note that at this point, the voice -frequency spectrum is inverted (e.g.,the frequencies that were low nowbecome high, and vice versa), mak-ing the voice signal completely unin-telligible. That means that it is nownecessary to reverse the modulationprocess to recover the voice signaland make it intelligible again. To dothat, the output of the first low-passfilter is fed to a second modulatorformed by U1 -c, U1 -d, and U3 -b,where it is frequency modulated withthe output of the second carrier os-cillator, comprised of U3 -c and U3 -d;the frequency of the second oscillatoris controlled by potentiometer R36.

The output of the second modu-lator is filtered by the second low-passfilter, which consists of U2 -d and fewsupport components, and amplifiedby Q3. The voice output signal fromQ3 is fed to U4 (an LM386 low -voltage, 73

74

MICROPHONE MODULATOR

AUDIOAMP

4kHzOSCILLATOR

5kHzLOW-PASS

FILTER

MODULATOR

4kHzVARIABLE

OSCILLATOR

5kHzLOW-PASS

FILTER

OUTPUTAMPLIFIER

SPEAKER

Fig. 1. As shown by this funct.onal block diagram of the Voice Disguiser, the circuit iscomprised of a microphone, audio amp, two oscillators (one fixed at 4 kHz and theother variable up to the same frequency), two 5 -kHz low-pass filters. two modulators,an output amp, and a speaker.

PARTS LIST FOR THEVOICE DISGUISER

SEMICONDUCTORSU I 4016 CMOS quad bilateral

switch, integrated circuitU2-MC3403 quad op -amp.

integrated circuitU3-4069 CMOS hex inverter,

integrated circuitU4--LM386 low -voltage, audio -

power amplifier, integrated circuitQI-Q3-PN2222 general-purpose

NPN silicon transistorLED1-Light-emitting diode

RESISTORS(All fixed resistors are 1/4 -watt, 5'%

units.)RI, RI2, R25 -10,000 -ohmR2, R7 -15.000 -ohmR3 -68,000 -ohmR4, RI8, R28 -2700 -ohmR5 -120 -ohmR6 -56,000 -ohmR8, R34 -1000 -ohmR9 -1000 -ohm potentiometerRIO, RI I, R23, R24 -100,000 -ohmR13 -10,000 -ohm PC -mount

potentiometerRI4, R35, R37 -5600 -ohmRI5-220,000-ohmR16, R26 -680 -ohmRI7, R27 -9100 -ohmR19, R29 -I50,000 -ohmR20, R30 -8200 -ohmR2I, R31--27.000-ohmR22, R32 -1500 -ohmR33 -10 -ohmR36 -10,000 -ohm potentiometerR38-R41--3300-ohmR42 -2200 -ohm

CAPACITORSCI, C3, C7, C12, C15, C21 -10-µF,

16-WVDC, electrolytic

C2, C5 C22 -C25 ---0.47-µF, 16-WVDC. electrolytic

C4, C6, C8, C9, C10, C17-0.005 -µF, ceramic -disc

C11, C13, C19, C20-0.05-ILF,ceramic -disc

04, C16, C18 -0.01-µ..F, ceramic -disc

C26 -0.001-µE 50-WVDC, MylarC27 -100-µF, 50-WVDC, MylarC28-4.7 1.1.F, 35-WVDC, Mylar


S1-SPST switchB1 -9 -volt transistor -radio batterySPKRI-4-8 ohm speakerMICI-Handheld microphone (see

text)TI -Audio output transformerPerfboard materials, enclosure, AC

molded power plug with line cord,battery(s), battery holder andconnector, wire, solder, hardware,etc.

Note: The following parts for theVoice Disguiser are available fromXandi Electronics, P.O. Box25647. Tempe, AZ 85285-5647;Tel. 602-829-8152 (generalinformation and catalogs);800-336-7389 (orders only). Anetched and drilled printed -circuitboard (part XV200B) is availabletbr $15.95; a parts kit (partXV200K) containing all resistors(including potentiometers),capacitors, transistors, integratedcircuits, and battery connector for$40.95. Please add $4.00 forshipping and handling. CODorders, add $6.00. Arizonaresidents please add 6.7% salestax.

audio -power amplifier) through animpedance -matching transformer, T1.The output of U4 is then used to driveSPKR1 (an 8 -ohm speaker). Note: U4 isoptional. Although the unit will workwithout U4, the output will be low butmore than sufficient for over -the -tele-phone use. If the amplifier is left out,capacitor 021 (in the emitter circuit of03) can be directly connected to aaudio impedance -matching trans-former (T1 as shown) and its outputused to drive a 4- to 8 -ohm speaker.

In operation, if both carrier os-cillators are set to the same frequency,the voice signal from the speaker willbe an exact duplicate of the inputsignal from the microphone. However,if the frequency of the second os-cillator is varied (via R36), the outputvoice signal also shifts in frequency.That makes the voice reproduced bythe speaker sound higher or lowerpitched than normal.

Circuit Construction. The Voice Dis-guiser was built on a printed -circuitboard, measuring about 313/46 by noinches. A template of that printed -cir-cuit layout is shown in Fig. 3 for those ofyou who wish to etch your own board.Or, if you prefer, you can purchase a kitof parts (including a pre -drilledprinted -circuit board) or the boardalone from the supplier listed in theParts List. Once you've etched or pur-chased your printed -circuit boardand gathered all the parts listed in theParts List, assembly can begin.

IC sockets should be provided forU1 -U3; besides serving as a circuit -board marker (allowing you to easilylocate the proper positions of the sup-port components), they also keep theIC out of harms way (soldering -ironheat) and allow you to make quickand easy replacements should thatever become necessary.

Figure 4 shows the parts -place-ment diagram. Start by mounting andsoldering the IC sockets to the board.Ned, install the resistors and capaci-tors. Be careful that the electrolyticunits are properly oriented. After that.carefully install the transistors (01-03),making sure that they are property ori-ented. Once all of the on -board com-ponents have been installed, con-nect short lengths of hook-up wire tothe appropriate points on the circuitboard for connection to the off -boardcomponents.

-IIB1 Si

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Fig. 2. Although, it might appear otherwise from this schematic diagram, the VoiceDisguiser is not very complicated. Note: The LM386 low -voltage, audio -poweramplifier (U4) is optional and was added to the main circuit to increase the circuit'soutput power. It may be left out of your project if desired, however, without it theoutput volume of the circuit will be greatly reduced.

You will note that the parts -place-ment diagram shown in Fig. 4 con-tains no previsions for U4 -the LM386audio -power amplifier, which is op-tional -or its support components(C26 -C28), nor does it have provi-sions for the audio transformer, T1. If

the amplifier is included in your proj-ect, it and its associated componentscan be wired together on a small sec-tion of perfboard, along with T1, and

1/4 MC3403

R3610K

FRE°

R355.6K

connected to the main circuit boardthrough short lengths of hook-up wire.Although an LM386 amplifier wasused to boost the main circuit board'soutput power, any other type of am-plifier can be used to boost the outputpower of the Voice Disguiser. Be care-ful when wiring the power amplifier, itseasy to mis-wire those components; infact, it's wise to double (or even triple)check your work to ensure that the

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circuit contains no errors.In any event, once your project

board(s) are completed, prepare theenclosure that will house the circuitboard(s). The author's unit was housedin a plastic project box with a metallid, measuring about 61/4 x 33/4 x 2inches. It will be necessary to drillholes in the lid of the enclosure forLED1, S1, R9, and R36, and to make acutout for SPKR1. It will also be neces-

4 313/1s INCHES

Fig. 3. The Voice Disguiser was built on a printed -circuit board, measuring about313/1,5 by 23/46 inches. A template of that printed -circuit layout is shown here full size forthose of you who wish to etch your own printed -circuit board. if you prefer, you canpurchase a kit of parts (including a pre -drilled printed -circuit board) or the boardalone from the supplier listed in the Parts List.

R9VOL

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C12,-R24- C15 \-R23-

U3

1C25

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NMI-66--R15-R14

-R37-4. /

-C14--R35-C24

I

-R41- R33

-R40- ra-C20)J- 1C21

-R32--R34

-C13- I

11TO AMPLIFIER

CIRCUIT

Fig. 4. Here is a parts -placement diagram for the author's printed -circuit layout. Youwill note that the LM386 amplifier is conspicuously absent from this parts -placementdiagram. Also missing are the amplifier's support components (C26 -C28), and dittofor the audio transformer (T1).

R36FREO

sary to drill a hole in the side of theenclosure through which to feed themicrophone cable. Once all of theholes have been drilled, mount andconnect the off -board componentsand amplifier circuit (if used) to theappropriate points on the printed -cir-cuit board. Note that there is no dedi-cated connection point on the boardfor LED1 or R42, the current -limiting re-sistor for the LED. Those components

were instead connected from batteryground to the "on" side of S1 (thepower switch) as shown.

Where the microphone is con-cerned, the author used one takenfrom an old video camera. However,you can use just about any micro-phone that you happen to have onhand. Although the microphone isshown (both in Fig. 2 and Fig. 4) asbeing a three -terminal (or wire) unit,

the circuit can also be fed by two -terminal unit, as the author did, byconnecting the microphone wire tothe upper and lower microphonepads on the circuit board,

Next we come to the speaker. Firstmount a speaker grille over thespeaker cutout. In the author's pro-totype, the grille was made from apiece of window -screen material,and secured to the lid with a siliconeadhesive. The speaker was thenmounted over the grille and securedwith more silicone adhesive.

The Voice Disguiser is designed forlow -power operation from a 9 voltbattery. If your unit is to contain theoptional output amplifier, you shoulduse a separate battery for the ampli-fier, so as not to siphon power from themain circuit board. That arrangementprovides longer battery life, while en-suring a steady and reliable output.

Circuit Checkout. Double check allcircuitry and make sure that all com-ponents are correctly installed in theproper location and with the properorientation. Next, connect a 9 -volttransistor -radio battery to the unit andturn it on. If you have an oscilloscope,use it to look at the signal at pin 12 ofU3, while adjusting R13 for a 4 -kHz, 8 -volt peak -to -peak, squarewave sig-nal. If no oscilloscope is available, setR13 to the mid range and R9 for max-imum volume. Make sure that thespeaker is connected. Tune a radio toa station transmitting voice only (nomusic), and place it near the micro-phone of the Voice Disguiser. Listen tothe sound from the speaker. Youshould hear the voice from the radio.By adjusting R36, you should be ableto shift the pitch of the voice.

Although the maximum audio fromthe speaker (without the optional au-dio amplifier) may not be very loud, itprovides more than enough volumeto drive the transmitter of almost anytelephone.

Note that if you are planning to usethe Voice Disguiser to transmit overthe telephone, it would be best tokeep the speaker of the Disguiser rightup against the telephone and keepthe handheld microphone away fromthe phone. The reason being is that ifthe microphone is too close to thetelephone, your regular speakingvoice will be also picked up by thetelephone microphone.

Have you ever been frustratedby your digital multimeterwhen trying to measure resis-

tance below one ohm? If so you'reprobably not alone because mostmeters will only measure resistancedown to the nearest 0.1 ohm. Well, inthis article we'll show you how to builda DMM accessory that will enable youto accurately measure a resistancedown to the nearest 0.0001 ohm. Theunit injects a precise amp of currentinto the resistance to be tested. Thenyou simply use your DMM to measurethe voltage drop produced by the in-jected current. With typical meters, re-sistances from 1 ohm to 0.0001 ohmcan be measured with the aid of thecurrent injector.

You should be able to find may usesfor the unit. I have used it to measureshunt resistors, circuit -board -trace re -

If your multimeter is

stumped when it comes to

reading very low resistance,

then this is the multimeter

accessory you should

build to extend

its range.

sistance, relay/switch contact resis-tance, and motor/transformer wind-ing resistance. You can even use it todetermine a wire's gauge by measur-ing its resistance per unit length or totest diode rectifiers or transistors at 1amp.

It has some nice features. For exam-ple the injector circuit is poweredfrom two "C" cells and features apower -on LED that doubles as aweak -battery indicator. Should thebatteries need to be replaced, theLED will fail to turn on during opera-tion.

How it Works. Figure 1 contains theschematic diagram for the One -AmpCurrent Injector circuit. The unit canbe divided into three main sections:power supply, current controller, andbattery -voltage monitor. Lets exam-ine the power -supply section first.

The circuit is powered by two "C"cells, B1 and B2. A pushbutton switch(S1), which connects the batteries tothe circuit, ensures that the systemonly draws power momentarily. Themomentary operation of the switchalso discourages prolonged mea-surement times, increasing thenumber of measurements that canbe taken before the batteries need tobe replaced. The large 100-µF ca-pacitor (C1) helps dampen transients

flows into the inductor (L1) from the 3 -volt battery supply. When pin 7 turnsoff, the energy stored in the inductoremerges as a short voltage pulse,higher in amplitude than the supplyvoltage. Those voltage pulses arerouted to a filter capacitor (C3)through a diode (D1). With the com-ponent values chosen, the voltageproduced at C3 ranges from about 9to 12 volts.

The current -control section uses a

Build a One -Amp

Current InjectorBY DAVID A. JOHNSON

caused by the heavy DC currentdrawn from the battery during opera-tion.

Because much of the unit's elec-tronic circuits function better at morethan 3 -volts, the circuit contains a sim-ple flyback voltage converter. It is

based on a CMOS version of the clas-sic 555 timer (U1) wired as a non-stan-dard astable oscillator. When pin 7 ofthe timer (used as an active -low out-put in this circuit) turns on, current

power MOSFET (Q1) to set the amountof current passed through the un-known resistance (12x). By controllingthe voltage applied to the gate termi-nal of the FET, it can be made to be-have as a variable resistor and can,therefore, vary the current as needed.

For that reason, one comparator inan LM393 IC supplies the FET with agate -control voltage. That section ofthe IC has been configured to oper-ate as an operational amplifier with 77

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1WATT""sak

Fg. I. The current injector can be broken down into three sections: the power supply(containing a DC -to -DC converter), a current -control circuit, and a battery monitor.

the aid of a resistor (R9) and a capaci-tor (05). The two components form afilter network that helps stabilize thevoltage fed to the FET. A regulatedvoltage, developed by a voltage -ref-erence IC (U3) and a resistor (R5), isconnected to the noninverting inputof U2 -a through a voltage -divider net-work consisting of R6, R7, and R8. Thenoninverting-input voltage sets thevoltage level controlling the FET. Po-tentiometer R7 allows you to selectthe value of the noninverting-inputvoltage so you can precisely adjustthe injector's output current to 1 -amp.

The injector's output current, whichpasses through the unknown resis-tance and the FET (Q1), is also forcedthrough an internal current -monitor-ing resistor (R10). The voltage de -

cif) veloped across R10 is thereforeproportional to the injector's outputcurrent. The current -monitoring volt-age produced by R10 is fed to theinverting side of the control IC (U2 -a).

mSo the IC's output supplies the gate of0 the FET with the correct voltage to

maintain the unit's output current at afixed level.

Diode D3 and capacitor C6 arewired across the output terminals asprotection. They absorb any energy

W that may be sent back to the circuit ifa) vni happen to measure a resistor witha)

a large inductance.78 The battery -monitor section also

performs an important task. With twofresh "C" cells installed in the unit, anominal 3 -volts is supplied to the cur-

operation, the battery voltage willdrop. The unit will continue to operateproperly as long as the battery volt-age remains above 2 -volts. The bat-tery monitor's job is to light the powerLED (LED1) as long as the battery volt-age remains above 2 -volts. Shouldthe circuit need new cells, the LED willfail to turn on.

To do its job, the battery monitoruses the second half of the dual -com-parator IC (U2 -b). It is wired as a classicvoltage comparator. The regulatedvoltage from the voltage reference IC(U3) is compared to a voltage de-veloped by a voltage divider (madeof R3 and R4) that is connected to thecells. As long as the voltage from thedivider is greater than the referencevoltage, the output of the comparatorremains low, turning on the power in-dication LED.

Construction. As illustrated in Fig. 2,the unit's circuitry is housed in a proj-ect box (the author's was plastic) thatyou can purchase from almost anyelectronic -parts supply store. Usingthe figure as a guide, first glue a iwo"C" -cell holder to the inside bottom ofthe box, with the holder pushed toone end. Drill two 5/32 -inch holes

PARTS LIST FOR THE ONE -AMP CURRENT INJECTOR

SEMICONDUCTORS1_11-TLC555CP CMOS oscillator

timer, integrated circuitU2-LM393N dual comparator,

integrated circuitU3-LM385BZ-I.2 voltage

reference, integrated circuitQI-IRF521 or IRFZ12, 50 -volt. 0.3 -

ohm power FE ID1 -1N4148 general-purpose diodeD2 -1N4001 50-PIV

rectifying diodeLED1-Light-emitting diode, red,

super -bright T-1 style

CAPACITORSCI -100-µF. 10-WVDC, aluminum

electrolyticC2-1000-pF, 50-WVDC, ceramic or

MylarC3 -10-µF, 25-WVDC, aluminum

electrolyticC4, C5 -0.l -µF, 50-WVDC, ceramic

or Mylar50-WVDC, Mylar

RESISTORS(All fixed resistors are 1/4 -watt 5%

units unless otherwise indicated.)R1 -82,000 -ohmR2 -100 -ohmR3 -10.000 -ohmR4--15.000-ohmR5 -3300 -ohmR6-l8.000-ohmR7 -500 -ohm multi -turn trimmer

potentiometer (Digi-Key CEG52 orequivalent)

R8 -1300 -ohmR9 -100,000 -ohmR10 -0.1 -ohm, 1 -watt. (Digi-Key

SCIA0.1 or equivalent)


BI, B2-alkaline "C" cellL1-4.7-mH choke coil (Digi-Key

TK4320 or equivalent)SI-Normally open, SPST,

momentary -contact switchPrinted -circuit or perfboard, LED

holder, 2 "C" -cell holder,enclosure, transistor heat sink, redand black hook-up wire, alligatorclips (or equivalent), solder, etc.

through the other end of the box toallow the injector's Iwo current -carry-ing wires to exit. Then drill a 3/8 -inchhole for the power switch and a 1/4 -inch hole for an LED holder throughthe top cover of the box. With theholes drilled, you can then install the

218/32

43/4

BOX LID

ALL DIMENSIONS IN INCHES

REDBATTERY

HOLDER

LEADS

BLK

18/32

51/64

F. 11/2

HEAT SINK

C CELL

C CELL11

CIRCUITBOARD

COMPONENT PLACEMENT INSIDE BOX

KNOT

Fig. 2. if you drill your enclosure to these specifications you'll make the task of finalassembly a lot easier. Remember to use a holder for the LED.

Fig. 3. Using this foil pattern togenerate a printed -circuit board willmake the assembly of your own currentinjector a snap.

power switch and the LED (with aholder) in the top of the box.

Next, you'll need to build the rest ofthe circuit on a suitable platform. ThecIrcuit is not complicated and couldeasily be built breadboard -style. Alter-natively, if you wish to, you can etchour own printed -circuit board using

me foil pattern shown in Fig. 3. Consultthe parts -placement drawing (seeF.c. 4) for the correct componentplacement, being careful to note thecrientation and polarity of the com-ponents.

U1

eLED1S1

0 0

together as shown in Fig. 4. Solder allconnections.

The next step is to prepare two testleads. Use standard No. 20-18 gaugered and black wires about 36 incheslong. First solder alligator clips or othersuitable probe tips to the end of thetest lead wires. Next, feed the twowires through the holes in the end ofthe box. Once through the hole, tie atight knot about 1 inch from the end ofeach wire to act as a strain relief. Fi-nally, solder the leads to the indicatedpoints on the circuit board, paying at-tention to the polarity-red forpositive and black for negative

With everything installed, inspectthe connections to make sure you fol-lowed the schematic and parts -placement diagram exactly. If you aresatisfied everything is in order, you caninstall the two "C" cells. The unit stillmust be calibrated, so do not installthe lid at this time.

Unit Calibration. You will need agood digital multimeter to accurately

R7

TO D.U.T.D.U.T.

Fig. 4. Follow this diagram to stuff the circuit hoard. Be sure to orient all thepolarity -sensitive parts properly as you proceed.

+

B1 B2

R10

01

When you install the FET (Q1), makesure that its body is about 0.15 inchesabove the board and that it is prop-erly heat-sinked. Once you have sol-dered all the parts in place, carefullyinspect the board for solder splashes,shorts, and misplaced componentsbefore moving on.

Next, use pieces of small gauge(No. 28-24) wire to connect the circuitboard, battery holder, LED1, and S1

calibrate the unit. Before connectingthe injector's output to the digital mul-timeter's leads, make sure the meter isset to measure DC amps (usually on a2 -amp scale), and not DC milliamps.If you mistakenly set the multimeterto the milliamp or microamp scale,the 1 amp of current from the injec-tor could blow the meter's protec-tion fuse.


80

With this project, you need not be able to see adial pointer to determine the direction in which you are headed.

This project came about as aresult of a search for a quickand easy method to provide

telemetry for a remotely piloted vehi-cle (RPV)-in this case, a radio -con-trolled airplane carrying a videocamera and IV transmitter. From a lo-cation on the ground, that set-up al-lows the pilot to watch a IV monitorand guide the plane through itspaces without actually seeing theplane.

Unfortunately, with the plane flyingso far away from the "home 40," it iseasy to become disoriented and loseyour sense of direction, which canmake returning the plane to homebase very difficult if not impossible.That's when I decided that an on-board compass would be necessaryto avoid losing the plane. And sincethe pilot (myself) would not be in thecockpit where the compass headingmight be checked, it was decidedthat an audible compass (whose out-put could be relayed by an audio in-put on the IV transmitter) was theeasiest way to transfer that vital infor-mation to the pilot. That lead me todevelop the Talking Compass that isdescribed in this article.

Circuit Description. Figure 1 showsa schematic diagram of the TalkingCompass. The circuit is comprised of adirectional sensor (or digital compass,MOD1), an ISD1016 analog storagedevice (U2), a 74S188 preprogram-med PROM (U3), and a handful of ad-ditional components.

The ISD1016, which is designed torecord and playback analog signals(such as voice) will hold the recordedsignal for more than ten years evenwith the power off. The chip provides atotal storage time of 16 -seconds,which can be used in one shot, orbroken up into smaller segments. Thesegments can be as short as a tenthof a second. Because each tenth of asecond of the total storage time is fullyaddressable by way of the chip's 8 -bitbinary address (pins 1 through 7, and9 and 10), messages can be recordedon those small segments and individ-ually selected for playback by ac-cessing the proper address bus.

In our application, the total time isdivided into eight 2 -second seg-ments. The starting point addresses forthe eight 2 -second segments are lo-cated at the binary equivalent of 1,20, 40, 60, 80, 100, 120, and 140. By

placing one of those binary numberson the chip's address bus, a two sec-ond word or phrase can be recordedand/or played back.

Directional information is providedby MOD1, which uses a subminiaturejewel -suspended magnet sur-rounded by four Hall -effect IC's. In use,the Hall -effect device that is directlyopposite north turns on, causing itsoutput to go to ground. The other out-puts are held high by pull-up resistorsR13 through R16.

As the sensor is rotated (say be-tween north and east) two of the Hall -effect devices will be directly op-posite north, so they both will turn on,thereby giving the intermediate di-rection (in the above example, north-east). The digital compass (MOD1)outputs directional information as a 4 -bit binary code. That 4 -bit informationis transformed into 8 -bit binary databy integrated circuit U3-a 256 -bit bi-polar PROM. Table 1 is the truth tablefor the 74S188 PROM.

The 8 -bit data is used to select spe-cific starting point addresses on theISD1016 (U2), which can then be re-corded to; or, if a message has beenrecorded at the specified address, it

R1310K

MOD1

20 02

3o o2 1

o3

OFF o p 0I ON

I

R1410K

1016

R5

10Kt R6

.101( R7

10K

--R8

10K R910K

t R1010K S 1111

10K

t R1210K

1

7 211

6 3

R15 S 5 4

10K 4'12

U3748188

4 5

3 6

R16 S 2 9

10K 7 ' 10

8 2344A.

14 115 R310K S2

PLAY =3 27oREC

D1

?

1N4001U1 19--

7805

B1

9V .

+-I- C1% 22

C6

4.7R4

47K

II

Fig. 1. The Talking Compass is comprised of a digital compass (MOD1), an 1SD1016analog storage device (U2), a 74S188 preprogrammed PROM (U3), and a handful ofadditional components.

TABLE 1-74S188 TRUTH TABLE

Directory Input Output

DecimalEquivalent

A4 A3 A2 Al AO BO B1 B2 B3 B4 B5 B6 B7

North L H L H H 0 0 0 0 0 0 0 1 1

N.W. L L L H H 0 0 0 1 0 1 0 0 20

West L L H H H 0 0 1 0 1 0 0 0 40

S.W. L L H H L 0 0 1 1 1 1 0 0 60

South L H H H L 0 1 0 1 0 0 0 0 80

S.E. L H H L L 0 1 1 0 0 1 0 0 100

East L H H L H 0 1 1 1 1 0 0 0 120

N.E. L H L L H 1 0 0 0 1 1 0 0 140

can be played back, Switch S3 is usedto select the mode of operation; rec-ord or playback. Switch S2 enablesthe recording or playback processchosen by S3. Diode D1 at the input toU1 (a 7805 5 -volt voltage regulator)protects the circuit in case the batteryis connected with its polarity reversed,which would ruin the compass sensor.The speaker connects directly to U2,which has its own output amplifier.

Construction. Begin by making aprinted -circuit board; a full-sizeprinted -circuit pattern is provided inFig. 2. After etching and drilling theboard, clean the traces with steelwool and check for shorts.

Begin assembling the board by in-stalling IC sockets for U2 and U3,guided by the parts -placement di-agram shown in Fig. 3. Follow that withthe resistors and the capacitors; thendiode D1, the digital compass

(MOD1), and the voltage regulator(U1). Solder wires to the appropriatepads on the board for connection tothe off -board components (batteryconnector, speaker, switches, and mi-crophone).

Once the circuit has been checkedfor faults, put the assembly aside for awhile, and prepare the enclosure thatwill house your project. The circuitmust be housed in a non-magneticenclosure (such as Radio Shack's#270-223 plastic project box). What-ever housing you select, make surethat it allows the speaker to be sepa-rated from the digital compass by atleast 4 inches (center to center) sothat the speaker magnet will not af-fect the operation of the compass.

It will be necessary to drill mountingholes in the side of the enclosure forthe switches. A hole for the micro-phone along with speaker grille holesshould also be drilled in the lid of the

16

U2

18E11018

28

12

13

C3

.1

R1

10K

C4

20 .22

/ N

C

21

14

154A0*R2

10c1

C2

1

(SPKR1

enclosure. Once the holes have beendrilled, mount the off -board compo-nents to the enclosure. The speakercan be mounted using silicon sealeror some other suitable adhesive. Themicrophone element can be securedto the lid of the enclosure by placing arubber grommet in the microphonehole and just pressing MIC1 intoplace.

Once the off -board componentshave been mounted to the enclosure,install the circuit board and connectthe off -board components to the cir-cuit board using hookup wire. Be surethat when the lid is attached to theenclosure, the compass is located atthe end opposite the speaker, Labelthe playback/record (S3) and on/off(S1) switches.

Install a battery using double -sidedfoam tape to hold it in position andcheck for correct voltage at U2's andU3's power terminals. Also check forcontinuity to common at the groundterminals of those IC's. Next install thetwo DIP IC's (U2 and U3). Rememberthat the ISD1016 is a CMOS device,and is thus sensitive to electrostaticdischarge.

Now comes the moment of truth.

Operation. To record a message,place S3 in the REC (record) positionand apply power to the circuit. Rotatethe box to the direction (east, west, 81

PARTS LIST FOR THE:ALKING COMPASS

SEMICONDUCTORSL1-7805 1 -amp. 5 -volt, voltage

regulator, integrated circuit1.12-1SD1016 analog storage device.

integrated circuitU3 -74S188 256 -bit PROM

(preprogrammed). integratedcircuit

MODI-Dinsmore digital compassDI-IN4001 1 -amp. 50-PIV, rectifier

diode

RESISTORS(All resistors are V4 -watt, 5% units.)RI, R3, R5-R16-10.000-ohmR2 -10 -ohmR4 -470,000 -ohm

CAPACITORSC1-22-tif. 16-WVDC, tantalumC2, C3 -0.1-µF, ceramic -discC4-0. 22- µF, ceramic -discC5-l-µE 16- wVDC, axial -lead

electrolyticC6-4.7-41, 16-WVDC, axial -lead

electrolytic


Si. S3-DPDT slide switchS2-SPST momentary pushbutton

switchSPKR1-8-ohm, 0.2 -watt. 2 -inch

speakerMIC1-Electret microphone elementB1 -9 -volt transistor -radio batteryPrinted -circuit materials, enclosure,

9 -volt battery holder andconnector, grommet, adhesive,wire, solder, hardware, etc.

Note: The Digital Compass (MOD1).part #1490, is available fromDinsmore Instrument Co., 1814Remelt St., Flint, MI 48503, for$12.00 each, plus $0.52 postage.Michigan residents must addappropriate sales tax.

The ISD1016 analog storage chip(U2 is avalible from InformationStorage Devices, Inc., 2841Junction Avenue, Suite 204, SanJose, CA. 95134, for $27.99 eachpostpaid. California residents mustadd appropriate sales tax.

The 74S188 256 -bit preprogrammedPROM 1U3) is available fromFuntech, P.O. Box 772747,Houston, TX 77215-2747, for$5.99 each postpaid. Texasresidents must add appropriatesales tax.

r -

es INCHES

Fig. 2. Here is a full-sized template of the printed -circuit artwork used to produce theauthor's prototype unit. After etching and drilling, the board, clean the traces withsteel wool and check for shorts.

R16

I R108111 I

I I

R12

PLAY

U2

R2

SPKR1

REC

R3

C5,+

-R4--G4-

R1--- -C3

sONi

MIC1

""r"S2

Fig. 3. Assemble the board guided by this parts -placement diagram, beginning withthe IC sockets for U2 and U3, followed by the resistors and the capacitors; then diodeDI, the digital compass (MODI), and the voltage regulator (UI).

north, or south) that you want to rec-ord and make sure that the project islevel. Press S2 and speak into MIC1.When through speaking, release S2 tostop recording. You have two secondsto record your phrase or word. Youcould say "north" or a quick "you'refacing north." I have found it better toface off to one side while speaking sothat your breath does not hit the mi-crophone and produce wind noiseswhen recording "s" and "th" sounds.

Check the recording by placing S3in the PLAY (playback) position, andwith the box pointed in the same di-rection momentarily press S2. Thecompass should play back whatyou've recorded. It is not necessary to

hold S2 down; just a quick press andrelease is all it takes.

Go through the recording processwith all 8 direction points, positioningthe compass to point in each direc-tion. Remember that the sensor is in-ternally damped and it takes acouple of seconds for it to stabilize inthe correct direction when setting upfor recording or playback. If you at-tempt to record messages that arelonger than two seconds, the record-ing will run over into another sectionand erase whatever might have beenstored there. But it is a simple matter tore-record both.

It is possible to playback everything(Continued on page 102)

BY TERRENCE VAUGHN

Using a cable -ready VCR as atuner can, in many cases, savethe cost of renting a cable

box. Unfortunately, doing so means al-ways having to turn two units (both theTV and VCR) on or off due to the lackof switchable accessory outlets. Ad-mittedly, that's a minor annoyance,but it is a constant one. Tiring of thatinconvenience, I came up with theVCR/7V Auto -Switch described in thisarticle.

What the VCR/TV Auto -Switch doesis monitor the baseband-video outputof your VCR. When a video signal isdetected, the VCR/TV Auto -Switch au-tomatically turns on your TV set or vid-eo monitor. Note, however, that thisapproach will not work with a televi-sion that stores channel or volume in-formation in a volatile memory.

How It Works. A schematic diagramof the VCR/1V Auto -Switch is shown inFig. 1. The circuit is comprised of a 24 -volt center -tapped transformer (11), a1 -amp, 100-PIV fullwave bridge rec-tifier (BR1), and two 12 -volt regulators(U1 and U2), which form a dual -polar-ity, regulated, power supply; a dualBiFET op -amp (U3) and a general-pur-pose NPN silicon transistor (Q1), whichform the basis of a signal detector/trigger circuit; a 12 -volt relay (K1); twoAC sockets (S01 and SO2); and a fewadditional components.

A voltage divider formed by R5 andR6 provides a very small positive offsetto the inverting inputs of both U3 -aand U1 -b to help prevent false trigger-ing. The circuit takes its input from thebaseband-video output of your VCRvia PL2 (an RCA plug that mates withthe video -output jack of the VCR).When switches S1 and S2 are in thepositions shown and the VCR is turnedoff, no signal is applied to the circuit(through PL2), so the input to op -ampU1 -a is at zero volt, forcing its outputlow. That low is applied to the non -inverting input of U3 -b, forcing its out-put low. The low output of U3 -b holdsQ1 at cutoff, keeping relay K1 fromenergizing, and the TV connected toSO2 from turning on. Note that whenthere is no signal present, the outputof U3 -b swings close to the negativesupply rail, producing a negative volt-age that exceeds the emitter -basebreakdown voltage of Q1. Diode D2's

AutomaticPower Switch

Add an accessory outlet to your video system thatturns on your TV whenever your VCR is turned on

function is to block the negative go-ing output of U3 -b, thereby prevent-ing damage to Q1.

On the other hand, when the VCR isturned on, a baseband-video signal isapplied to the circuit at PL2. That sig-nal is routed to the non -inverting inputof U3 -a, causing the output of that op -amp to swing positive. The output ofU3 -a is fed through diode D1 (whichpasses only the positive portion of thesignal), causing C11 to charge. DiodeD1 also prevents the charge on C11from being discharged through U3 -aduring U3-a's negative -going outputtransition. The charge on C11 is bledoff via R7 during the negative -goingoutput transition and power is re-moved from the circuit. The C11/R7combination also forms a glitch filter,which provides a short time -delaythat prevents a momentary signal lossfrom cycling the television or monitoroff and on.

The output of U3 -a is applied to the

non -inverting input of U3 -b, causing itsoutput to go high. That high is appliedto the base of Q1 through D2 and R8,causing Q1 to turn on.

When Q1 conducts, it, in turn, com-pletes the ground path for the relay,causing it to energize. With the relayenergized, AC line voltage is appliedto SO2, automatically turning on theTV Diode D3 is used to protect Q1 fromthe inductive kickback (spikes)caused by the relay's collapsing field.Without that protection, an inductivespike could cause Q1 to short, turningit into a three-legged Zener diode.That would result in the TV being oncontinually.

Switch S1 allows you to choose be-tween auto and manual operation.When S1 is placed in the MANUALposition and S2 is set to the ON position,a positive voltage from the powersupply is applied to the non -invertinginput to U3 -a, causing the TV to turn onas if the circuit were in the auto mode

PL2

VgtFROMVCR

3 1N., I

24VCT450mA

C2

470

R3

4AUTO10K

S1 MANUAL

POON

S2 R2OFFI 10K

VN

R1

10K

U1

7812

0

G

C4

.1U2

7912

PL1

117VAC

C54C77.1

-I-C6.1 ^

+- C8

R4:100K

R64700

D1

1N914

1

1/2 LF353N C471

NC10

.1

VA- R7100K

+ C91

22

-12V

sotVCR

SO2TV

Fl3A

+ 12V

D21N914

R847K

D31N914

0

K1

12V

012N2222

Fig. I. The VCR/TV Auto -Switch is comprised of a 24 -volt center -tapped transformer (TI), a 1 -amp, 100-PIV, fullwave bridgerectifier, and two 12 -volt regulators (UI and U2), which form dual -polarity, regulated, power supply; a dual BiFET op -amp (U3) anda general-purpose NPN silicon transistor (QI), which form the basis of a signal detector/trigger circuit; a 12 -volt relay (KI); two ACsockets (501 and S02); and a few additional components.

and a video signal from the VCR were wire. Mount the relay to the board should be of the type that has break-present. and connect short lengths of wire to away tabs between the two outlets. As

the relay contacts. Do not connect shown in the schematic diagram, theConstruction. As shown in the pho- the relay -contact wires to SO2 and cold (or neutral, large -spade side) re-to, the author's prototype of the VCR/ the AC line at this point; you will be mains as normal; however, the two hot1V Auto -Switch was assembled on a instructed when to do so later on, dur-tabs have been separated, with thesection of copper -clad experi- ing the checkout procedure. hot side of SO1 going directly to thementer's board and point-to-point Note that the circuit contains two AC line, and the hot side of SO2 goingwiring was used to make the compo- AC sockets (S01 and S02): The two to the relay's wiper.nent interconnections. When assem- sockets are actually a single, standard For safety reasons, it is also impor-bling the circuit, all of the standardproject -building precautions apply:

duplex AC wall -outlet. The socket tant that the duplex socket (which is

Keep all leads as short as possible,and all power -supply bypass capaci- BEND 90'

tors (C3-C6, C9, and C10) should bemounted as close to their respective

0IC's as possible. It is also recom-mended that an IC socket be pro-vided for U3 (the op -amp).

Because 117 -volts AC is applied tothe circuit board via the relay, theboard must be securely mounted onstandoffs. In addition, wire connec-tions to the relay should be made withwire of sufficient size to handle the AC -line voltage. Instead of enlarging thepre -drilled holes in the experimenter's Fig. 2. For important

A

saftey reasons, it's also

B

that the duplex socket mounted to theboard to accommodate 18 -gauge rear panel of the enclosure be able to withstand power -cord insertion force without the(line -cord size) or heftier wire, the au- case flexing and possibly forcing the AC wiring to contact the case or otherthor used dual strands of 20 -gauge components. To that end, reinforcing brackets fabricated from scraps of sheethook-up wire for the relay, which is aluminum were placed at one end (either end) of the outlet, although placing bracketsmore than equal to a single 18 -gauge at both ends makes for a much sturdier project.

Here is an inside view of the VCRITV Auto -SIB In the prototype, fit J'1 is not theboard -mounted type; instead the author chose to use an in -line fuse. The enclosure forthe project has enough space for the circuit board, as well as all of the off -boardcomponents.

Once the project enclosure has been drilled, labels can be affixed to the front and rearpanels to indicate switch functions, and outlet designations.

mounted to the rear panel of the en-closure in the prototype) be able TOwithstand the power -cord insertionforce without the case flexing andpossibly forcing the AC wiring to con-tact the case or other components. Tothat end, reinforcing brackets fab-ricated from scraps of sheet alumi-num were placed at one end (eitherend) of the outlet, although placingbrackets at both ends makes for amuch sturdier project. Figure 2 givesdetails on how to fabricate the brack-et(s).

Since the project is intended to bein constant use, it does not have apower switch; however, adding onecertainly wouldn't hurt anything. It is

essential that a polarized AC powercord be used to connect the circuit to

the AC source. That's because the re-lay can interrupt only one line andthat really should be the hot (smallspade) side of the AC line cord. Mod-ern electronics gear (particularlyVCR's and TV's) may (and often do)also require the correct polarity. Athree -wire plug and cord (with theground wire connected to the case) iseven better for PL1.

When it comes to PL2, you have acouple of options: You could use ajack instead of a plug for PL2, and usean RCA patch cord to connect thecircuit to your VCR; or you can do asthe author did, cut the connectorfrom one end of a patch cord andconnect the wires directly to the cir-cuit board. With the latter arrange-ment, you could simply plug the unit

PARTS LIST FOR THEVCR,TV AUTO -SWITCH

SEMICONDUCTORSU1-7812 12-,

voltage rein .1'

U2-7 "volt

U3-I.'

posit, \I.uit

nega.'sited c s nitual Bit LT

op -amp. IntQ1 ?N geaLiai -purpose NPN

,,istorDl -1) IN914 general-purpose,

smai: signal diodeBRI-1-amp, 100-PIV, fullwave

bridge rectifier

RESISTORS(All resistors are 1/4 -watt, 5% units.)R1 -R3 -10,000 -ohmR4, R5, R7 -100,000 -ohmR6 -470 -ohmR8 -47,000 -ohm

CAPACITORSCl, C2 -1 -I1 -µF, 35-WVDC,

electrol \C3 -.C6, C': +_'10 0.1-µF, 50-

WVP( .!inolithic-ceramic orcei,.'

35-WVDC, electrolyticCS F WVDC, electrolytic

,.,-WVDC, tantalum

ADDITIONAL PARTS ANDMATEfilALS

1 i-24MA Inv,

Fl -3K I

s I ,

I),

15t) -

SI, IT toggle switchPL1-Polar AC power plug with

line ordPL2-- ,ieo dubbing (patch) cord,

seeSO1. s,i'-117-volt duplex NC outletFxpe nter's board, end, are, fuse

in socI-or wire,

into the VCR's baseband-video out-put.

If you opt for the latter arrange-ment, cut off one of the RCA plugsand carefully remove one inch of thethin outer insulation, exposing thebraided sheath. Bend the cable atthe end of the insulation and spreadthe braid away from the bend. Pull theinner cable through the opening inthe braid. Strip about 1/2 inch of insula-tion from the inner cable. Connect


((Does your present lure fail to attractthe fish to your line? If so, perhaps anilluminated lure will change your luck,and enable you tocatch the big onethat always seemsto get away.

It rained all weekend again. I hadplanned to go fishing but it justwasn't in the cards. So, I thought I

would tinker around with my electronicstuff and wait for the rain to stop. Ob-viously, my heart wasn't in it, becausewhat grew out of that weekendwas a strange, but effective, fish-ing lure. Perhaps, it is stretchingthe definition of "electronics" tocall it an electronic device, butit does use electricity and insome mysterious way it commu-nicates with fish.

The lure is the essence ofsimplicity (see Fig. 1). Using a paperclip, a calculator battery, and a light -emitting diode (LED) or micro lamp, youcan make an effective multi -purposefish -catching device and amaze yourfriends at the same time. If you're likeme, your friends have come to expectstrange ideas from you and this devicewill certainly strengthen that image. I

think it may even be legal, but you bet-ter check the local laws governing yourfavorite fishing hole to be sure.

The lure consists of a large paper clip,a flat, wafer -type battery (1.5 or 3 volt),an LED or micro lamp, a treble hook,and a pair of needle -nose pliers. Theauthor's version uses a 3.0 -volt lithiumbattery (CR-2430), but the lure can bemodified to use any size wafer battery.There is one problem though; if you aregoing to use an LED as the light source,you'll need to use a 3 -volt battery. Ittakes 1.6 volts of junction potential to"light" an LED and the 1.5 volt batteriesjust don't have enough voltage.

How it Works. The circuit behind thefish lure (see Fig. 2) is so simple-a bat-tery, resistor, and a lamp --that it is al-most not worth showing. A resistor canbe added (as shown) to limit currentthrough the light -producing elementand to regulate the brightness of thelight, but it is not usually needed becausethe internal resistance of the battery willkeep the current at about 33 mA.

Buildan

ElectronicFishingLure

The prototype unit used a 1.5 -voltlamp powered from a 3 -volt battery.That's a bit over the lamp's designedvoltage, and tends to shorten both bat-tery and lamp life a bit. However, theextra brightness is attractive to the fishand since catching fish is what this is allabout, operating the lamp a little "hot-ter" than the lamp designers had in-tended seems a worthwhile tradeoff.

You can use either an LED or microlamp. You can even use one of thoseflashing LED's, but make sure it can op-erate from a 2.5 -volt source. I havefound that in the waters around my

BY JERRY BAUMEISTER

home, diffused yellow LED's work bestfor black bass. (I don't know why. I guessit's just part of the mystery that makesfishing so interesting.)

Water proofing was not necessary forthe ponds where I fish. The resistance oflocal pond water around here is about10,000 ohms per cm. Since the resis-tance through the lamp circuit is about11 ohms, most of the current flowsthrough the lamp circuit and not thewater (current follows through the pathof least resistance). The resistance ofthe circuit using an LED instead of amicro lamp is a bit higher, but it is still low

LED OR LAMP

Fig. 1. The Electronic Fish Lure wascreated from an ordinary paper cliptwisted so as to hold the leads of an LEDin contact with both poles of a battery.

PARTS LIST FOR THEELECTRONIC LURE

LEDI-Light-emitting diode or microlamp

RI --Optional. see textI31 -1.5 -3 -volt, flat wafer -type,

calculator battery, see textPaper clip, cellophane tape, thin -plastic

or film insulating material (see text),treble hook, fingernail polish (seetext, etc.

B1

1.5-3V i

SEE TEXTLED1

Fig. 2. Here is the simple circui thatcomprises the electrical portion of theElectronic Fish Lure. Note: The resistor(RI) may or may not be needed; that willhave to be determined by experimentation.

enough to feed the lion's share of thecurrent through the lamp.

In chlorinated water, water that has ahigh ionic concentration, or in saltwater, water proofing is necessary. Alittle fingernail polish works just fine. Justpaint the entire lure, battery and all. Youcan even use different colors to jazz itup a little. I favor yellow lures with reddots, but use whatever color scheme orpattern that works for you.

The lure can be turned on and off byremoving the battery or by sliding asmall piece of plastic or film betweenthe battery and the point where itouches the lamp lead. Push the film in"o turn the lamp off, remove it to turn thelamp on.

Construction. The wire clip is every-thing. Take your time and get it right.Start, as shown in Fig. 3, by straighteninga large paper clip. Figure 3A shows the

B

C D

Fig. 3. Follow this clip -bending diagram to form the battery holder for the ElectronicFish Lure. Starting with a straightened large paper clip, make a bend at point A (A),follow by the bend at point B (B), and then the bend at point D (C). Then form a loop atpoint C and another at point E (D).

Here is the finished lure. Under some circumstances, depending on the c(?nauctivity of thewaters you fish, it may be necessary to insulate the electrical portion of the unit. Shouldinsulating be necessary, a coat or two of fingernail polish works well.

first bend, a 0.2 -inch, 90 -degree bend.With the bend pointing toward the ceil-ing, bend the wire to conform to thediagram in Fig. 3B. Next bend the last0.2 -inch of the double wire at point B inthe same direction as point A (towardthe ceiling).

Lay a battery, with cellophane tapecovering the negative side, on the wireform. The cellophane tape is to keepthe battery from shorting during con-struction. You will need to remove thetape before using the battery in thefinished lure. The positive ( + ) side of thebattery should be resting on the wire

and firmly against the bends at points Aand B.

Next bend the wire at point D towardthe ceiling forming a 90 -degree bendtight against the battery (as shown inFig. 3C). Bend the wire at point C andform a loop as shown in Fig. 3D. At thepoint where the loop reaches point D,bend the wire 90 degrees to the ver-tical and then again 90 degrees at apoint 0.2 -inch away to extend over thenegative side of the battery. Finally,bend a loop in the wire at point E asshown.

(Continued on page 99) 87

Laow -power amateur -radio oper-tion is challenging and fun.he thrill of making international

contact using a rig of less than fivewatts is really something to experi-ence. Low -power (or QRP) equipmenttends to be small and light, making itperfect to carry along on vacations.Unfortunately, some of the peripheralsneeded for a QRP station can be aslarge or larger than a complete QRPtransceiver. For example, commer-cially available antenna tuners areoften designed to handle upwards of200 watts, which means large induc-tors and capacitors. Because ofthat, the tuners are much largerthan needed.

But that needn't be becauseof the Tiny Tuner described inthis article. The Tiny Tuner is smallenough to fit in the palm of yourhand, and it is flexible enoughto match almost any piece ofwire that you might use for anantenna. That's accomplishedthrough an L -type filter network.

L -Type Filters. In its basicform, the L -type filter --sonamed for its resemblance tothe letter L - is built around twocomponents; either an inductorand capacitor (LC -type) or re-sistor and capacitor (RC -type).Such circuits can be used forimpedance matching, select-ing a band of frequencies fromamong many, etc.

Two L -type LC filters areshown in Fig. 1. Figure 1A showsan L -network configuration thatcan be used to match a low -imped-ance output to a 50 -ohm load (theantenna). Figure 1B shows an L -net-work configuration that can be usedto match a high -impedance outputto a 50 -ohm load.

Those filter circuits, in addition totheir impedance matching proper-ties, also provide low-pass filtering,which in our application, is well suitedto the suppression of harmonics in thetransmitted signal. A low-pass filter willpass all frequencies that are at or be-low its design parameters, while at-tenuating all others.

Although the two circuits shown inFig. 1 are configured for low-pass op-eration, they can easily be convertedto high-pass operation by reversingthe positions of the inductor and ca-

pacitor. The high-pass type filterwould, of course, pass only signals ator above the design frequency, whileattenuating all others.

Now let's take a look at our tunercircuit, which uses both of the circuitsin Fig. 1.

The Tuner. The schematic diagramfor the Tiny Tuner is shown in Fig. 2. Ascan be seen, the tuner is little more

to the load side of the antenna tuner(matching the high -impedance to a50 -ohm circuit of Fig. 1B), permittingyou to tune long antennas.

Tuning is handled through the in-ductor/switch combination. The in-ductor's 12 taps are connected to Thecontacts of a 12 -position rotary switch,S2. That switch is used to select thenumber of turns that will be includedin the circuit. The number of turns in-cluded in the circuit determines theelectrical length of the antenna; i.e.,the S1/L1 combo is used to electricallylengthen or shorten the antenna. In

that way, the antenna can bemade resonant at the frequen-cy of interest.

When S1 is in the off position(which takes the capacitor outof the circuit) and the inductor isset to zero inductance, a directpath to the output is providedthrough switch S2, thereby by-passing the antenna tuner.

"Tiny Tuner"If you've been having problems withyour QRP equipment this tuner may

be just what you need to optimizeyour rig for the frequency of interest

BY PHIL SALAS, AD5X

than a tapped inductor (L1), variable -capacitor (C1), L -type LC filter. The ca-pacitor is connected to the inductorthrough a center -off DPDT switch (S1),which allows the capacitor to be con-nected to either the input or output ofthe circuit. The switch enables the TinyTuner to provide either a step-up or astep-down impedance transforma-tion (depending on which extremethe switch is set to).

When S1 is set to "I" (input), the ca-pacitor is connected to the input(transmitter) side of the antenna tuner.That configuration matches the low -impedance to a 50 -ohm circuit in Fig.1A and therefore permits you to tuneshort antennas. When the switch isflipped to the "0" (output) position,the variable capacitor is connected

Construction. Because theTiny Tuner is comprised of so fewparts, there is nothing difficult

circuit. Infact, the most difficult aspect ofthe circuit's assembly lies inwinding the inductor, L1. ---andeven that is really quite simple.Inductor L1 was made from #24enamel -coated wire hand -wound on an Amidon Associ-ates (12033 Otsego Street,North Hollywood, CA 91607)1130-6 (yellow core) torroid coilform. When winding the coil,leave an extra length of wire at

the beginning of the coil; that willserve as the zero (0) tap. Then wind 21turns of the wire on the coil form. Asyou wind, make loops (which will formthe taps) at turns 1, 3, 5, 7, 9,11, 13, 15,17, and 19. As the loops are made,give them a twist close to the toroidbody (see Fig. 3) to hold the turns inplace. The taps should be equallyspaced around the coil form. Thathelps to place the taps In good posi-tion to be soldered to the contacts ofthe rotary switch. At turn 21, againleave an extra length of wire, whichwill also serve as a tap.

Once all 21 turns have been wound,snip off the ends of each loop, scrapethe enamel from the leads, individu-ally twist the pair of wires from eachloop, and then tin them. After tinning

J1

XMTR

A

J1

XMTR

J2ANTENNA

J2ANTENNA

B

Fig. 1. Here are two L -type, LC filters;the one in A can be used to match a lowimpedance to a 50 -ohm load, while theone in B can be used to match a highimpedance to a 50 -ohm load. Thosefilter circuits, in addition to theirimpedance matching properties, also actas a low-pass filter.

LI9µH 011

2119

0000-0 017151311 9

00 0

o S2 0-

0-00

7

-0

J1

XMTR

I 0 0S1/

C1

335pF 7"

Fig. 2. The Tiny Tuner is comprised of atapped inductor (LI) and a variablecapacitor (CI), which is connected tothe inductor through a center -off SPDTswitch (SI). That switch arrangementpermits the capacitor to be connected toeither the input or output of the circuit,thus allowing the circuit to emulate bothof the circuits in Fig. 1.

5

0

31

0

J2ANTENNA

all the taps, solder the inductor to a12 -position rotary switch. Assuming aclockwise rotation of S2, the turn -21tap should be connected to the firstswitch contact (making the first switchcontact the position of maximum in-ductance); The turn, 0 tap should beconnected to contact 12. Connectlengths of insulated hook-up wire tocontact 12 and the wiper terminal ofS2. They will be used to connect theswitch/inductor assembly to switch S1.Place the switch/inductor assembly tothe side, and begin preparing the en-

closure to accept the tuner.The author housed the prototype

unit in a 315/16 x 21/16 x 15/8 -inch plas-

PARTS LIST FOR THETINY TUNER

CI-335-pF tuning capacitorLI-See textSI-DPDT center -off toggle switchS2-SPI2T rotary switch11.12-BNC chassis -mount jacks


Amidon Associates T130-6 yellow -core toroid coil form, PAs x 21Asx 1'A -inch plastic enclosure.knobs, #24 enameled wire,miniature microphone cable orRG-174 coax, hook-up wire,solder, hardware, etc.

SCRAPE INSULATION,THEN TWIST AND TIN

Fig. 3. Inductor LI is comprised of 21 -turns of #24 enamel -coated wirehandwound on a T130-6 (yellow core)toroid coil form. When winding inductorLl, taps are made at turns 1, 3, 5, 7, 9,II, 13, 15, 17, and 19, with turns 0 and21 serving as the first and twelth taps.

tic project box. The metal lid of the boxwas used as the front panel of the unit.Prepare the lid by first drilling holes forthe unit's controls. A full-scale tem-plate of the Tiny Tuner's front panel is

shown in Fig. 4. The template can becopied or cut from the page, andused as a combination drilling guideand panel label.

If the template is to serve as a label,it should first be covered with clearplastic laminating film (the type usedto protect wallet ID's) and glued to thelid; if not, all that is needed are a cou-ple of strips of tape to hold the drillguide in place. In any case, drill holesat the three crosshairs. The center andleft holes (for the DPDT center -offswitch and variable capacitor, re-spectively) should be 1/4 -inch in diam-eter; the right hole should be 3/8 -inchin diameter (for the 12 -positionswitch).

Once the front panel has been pre-pared, mount S1, S2 (with inductor),and C1. The center position is re-served for S1; the capacitor and in-ductor (S2) positions are indicated onthe front panel by "C" and "L," respec-tively. Unfortunately, C1 (the 335-pFvariable capacitor) is not easilymounted. That unit is one of thoseflush -mounted jobs that have flat tun-ing knobs-that's the type used in por-table radios. Thus, it was necessary tomount that unit, and outfit it with aconventional knob, in an unconven-tional manner. To mount the variablecapacitor, first place the unit flushagainst the back side of the lid at theproper location. While holding it firmlyin place, apply a bead of hot -meltglue around the unit; allow the glue tocool before releasing it.

Once cooled, mount the flat knobto the capacitor's tuning shaft. The flatknob will be used as a base for mount-ing a more conventional knob. Turnthe capacitor fully counter -clockwise


C

max

Tiny TunerI

max

Fig. 4. The author's prototype unit was housed in a 315/16 x 206 x 11/4 -inch plasticproject box with a metal lid. If the same size enclosure is used to house your unit, thisfull-scale template can be used as a combination drilling guide and panel label.

00coaz

U)

5:coco0

0

0ww

C,rn

90

3)3 VISUALCONTINUITY

TESTERThis handy little tester doesmore than indicate acontinuous circuit path;it also gives a relativeresistance reading.

BY RICHARD HAMPTON

Whether you're an electronichobbyist or professional, ormaybe just an occasional tin-

kerer, one thing you simply can't dowithout is some sort of test equipment.One of the more basic test instrumentsis the continuity tester.

There are all kinds of continuity test-ers, ranging from a simple light bulband battery to sophisticated, commer-

TESTLEADS

R1 D1

10K 1N4003--104/4*14-

C1

0.1

I(

6

._E-11 B1 I++9V

U1 -b

/4 4011

2

13

cial-grade units. One drawback withthe majority of testers is that they indi-cate complete circuit paths only, withno indication as to the resistance in thepath. However, the 3 x 3 Visual Con-tinuity Tester described in this articlecan tell you more than just continuity: By

4 1/4 4011

U1 -c11

4

14/\\ 0 LED2 //LED1 0 0 LED3

131 12 11

U24024

101 B

)1C2

0.1

iD2N4003 8

R21MEG

2 3

9

4 5 6

LED4

LED5 0LED6

00 \

\O

LED7

Fig. 1. The 3 x 3 Visual Continuity Tester consists of two IC's, seven LED's, and ahandful of additional components.

judging the rate at which a particularLED flashes, you'll be able to estimatethe resistance.

Circuit Description. Figure 1 is a sche-matic diagram of the 3 x 3 Visual Con-tinuity Tester. The circuit consists of twoIC's (a 4011 CMOS quad 2 -input NANDgate, U1, and a 4024 binary counter,U2), seven LED's, and a handful of addi-tional components. All of the gates in U1are wired as inverters.

Two of the inverters (U1 -a and U1 -b)comprise an astable-multivibrator(free -running oscillator) circuit, whoseoperating frequency depends on theamount of resistance detected be-tween the test probes. Feedback fromthe output of the oscillator (at pin 4 ofU1 -b) back to the input of the circuit (atU1 -a, pins 1 and 2) is provided via C1.Resistor R1, along with the unknown re-sistance between the test probes, com-pletes the RC timing circuit. Thefrequency of the oscillator decreasesas the resistance between the test -probes increases.

The output of the oscillator is fed topins 12 and 13 of U1 -c, the output of

which then divides along Iwo paths. Inthe first path, U1-c's output is applied tothe clock input of U2 (a 4024 binarycounter) at pin 1; in the other path, thesignal is fed through D2 and across ca-pacitor C2, causing it to begin charg-ing. The charge on C2 is applied to U1 -d at pins 8 and 9. The output of thatinverter (U1 -d) is fed to the reset termi-nal (pin 2) of U2. If there is continuity or ameasurable resistance between thetest probes, U2's reset terminal is pulledlow, triggering the counter and allow-ing it to process the input pulses (count).

The rate of the count is proportionalto the resistance between the testprobes. If the resistance between thetest probes is low, the counter advancesrapidly. If a large resistance is detectedbetween the test probes, the counteradvances slowly. The counter providesa 7 -bit binary output that is wired toseven LED's.

When the test probes are placedacross a short circuit, LED7 flashes. If thetester is placed across a resistance of,say 2 megohms, LED1 will flash. In eithercase, the LED whose assigned valuemost closely corresponds to the resis-tance connected between the twoprobes will flash continually at a steadypace, while the other LED's will seem toflash intermittently.

PARTS UST FOR THE3 x 3 VISUAL

CONTINUITY TESTER

SEMICONDUCTORSUl-CD4011 quad 2 -input NAND gate,

integrated circuitU2-CD4024B binary counter,

integrated circuitDI. D2 -1N4003 1 -amp, 200-PIV,

rectifier diodeLEDI-LED7-Light-emitting diode

ADDITIONAL PARTS AND MATERIALSR I-I 0,000 -ohm, 1/4 -watt, 5% resistorR2-1-megohm, 1/4 -watt, 5% resistorCl, C2-0.1-111, ceramic -disc capacitorPertboard materials, enclosure, 9 -volt

transistor -radio battery, battery holderand connector, test -lead wire, testprobes, hook-up wire, solder,hardware, etc.

Note: An etched and drilled printed -circuit board is available for $5.00from Richard Hampton, 17005 E. 4thStreet South, Independence, MO64056; order part VC -3. Missouriresident.; add $0.29 state sales tax.

VC -3 1

VISUALCONTINUITY

-4121/6 INCHES 01

Fig. 2. The continuity tester was built on a printed -circuit board, measuring 3 x 3inches; here is the template for that printed -circuit board.

TESTLEADS

LED3 iaphri470K 11,i1Ur

LEN270K NOVI/

LED70

Fig. 3. Assemble the printed -circuit board using this parts -placement diagram as aguide. When assembling the project, be sure to pay attention to the orientation of thesemiconductors and battery polarity.

The circuit is powered from a 9 -voltbattery (B1). Since the circuit is off in thepresence of an open circuit, you canexpect a long battery life.

Circuit Construction. The continuitytester was built on a printed -circuit

board, measuring (what else?) 3 x 3inches. A template for that printed -cir-cuit board is shown in Fig. 2. A parts -placement diagram corresponding tothe Fig. 2 template is shown in Fig. 3.When assembling the project, be sure


Soldering -Iron ControllerTone down the temperature of any soldering iron with precession controller

5 oldering has always beensomething that requires a bitof experience to do properly.

However, even for the experienced,too -hot a soldering iron can lead totrouble. Sure you can go out and buyan adjustable -temperature solderingstation, but at great expense. Now thisis where the Iron Leash described inthis article comes into play; it will letyou adjust the temperature of any oldsoldering iron, although it's best withan iron of 25 watts or less-at leastwith the parts we've chosen. And the

0 best thing about the Iron Leash is thatO the circuit can be built for under 10coO dollars, depending on what parts youa may have on hand already.u) Not only is the device handy andin inexpensive, but it also uses some ordi-g nary parts in an extraordinary man-e° ner. So lets take a look at the circuit01 and see what makes it tick.U)0

gCurrent Regulation and More.cc Many of the circuits that appear in1-,(-3 these pages contain voltage reg-El ulators, and that's as it should be. Allg), circuits require power, and most dr-72 cults require it in the form of well be -92 hayed (read that "constant") DC, and

BY JOHN J. YACONO AND MARC SPIWAK

no IC is better at supplying tame DCthan the common voltage regulator.They provide excellent ripple rejec-tion. They are also very safe devicesand most shut off if overheated. Reg-ulators often have a short-circuit shut-down feature as well; if the load shortsout, the device's output shuts off.

As you may be aware, a subset ofthis important family of IC's are ad-justable. By using two resistors, you can"program" such a unit to supply volt-age at a desired level . .. at least that'stheir typical use. Many of them canbe used as current regulators andthey can even play a role in AC ap-plications.

In the normal course of operation,an adjustable regulator tries to main-tain a specific voltage called the ref-erence voltage (typically between 1.2and 1.5 volts, depending on the reg-ulator type) across an external resistor.The resistor in question is shown as R1in Fig. 1. It does that by producing cur-rent flow between its output and ad-just terminals. However, it limits thecurrent flow through the adjust pin toa bore minimum (typically from 40 to1001.4A depending on the tempera-ture and the particular regulator.) The

remainder of the current is forcedthrough R2. The combined resultingvoltage drop across R1 and R2 is thedesired output voltage.

By Ohm's law, since the regulatortries to maintain the voltage across R1at a specific value, the currentthrough that resistor (which is essen-tially equal to the current through R2)depends on R1's value. If we know theregulator's reference voltage (Vref) wecan set the value of R1 to deliver aprecise amount of current to R2 asfollows:

I = Vref/R1

If R2 is actually the load for the circuit,then the regulator and R1 form a cur-rent regulator for the load.

That technique should only be triedwith "floating" adjustable regulators.Floating regulators do not need to bereferenced to ground, so the loadcan be light or even shut off withoutcausing harm to the regulator. Manycommon adjustable regulators arefloating, so that is not a difficult re-quirement to fill.

To see how such a regulator mightbe used in an AC application, look atFig. 2. That is the circuit for the Iron

siftistrtrs.,w1.11,0

POSITIVEFILTERED

PULSATINGDC

POSITIVE -VOLTAGE

REGULATOR

ADJ

Vow

0

0

VREF

R2 R1

Fig. I. Floating adjustable regulatorscan be used as current limiters. ResistorRI programs the current flowing throughR2.

Leash. Integrated circuit U1 (a high -voltage regulator) is configured as acurrent regulator just as we've de-scribed. Resistor R1 limits the currentflow to an absolute maximum valueand R2 (a variable 5 -watt wire -woundresistor) allows the user to set the valueof current below that maximum.

The current regulator is placed be-tween the DC terminals of a bridgerectifier composed of D1 -D4. Thatmeans the regulator is only exposedto DC. However, the AC socket (S01)and AC plug (PL1) are both outside thebridge (i.e., in the AC portion of thecircuit). That allows the current reg-ulator to be in series with the AC legsof the circuit, and even control thecurrent through them, without directexposure to AC.

That is how the Iron Leash does it's

PL1

D1 D21N4001 1N4001

041N4001

S01

INPUT

OUTPUT

ADJUSTMENT

Fig. 2 This is the Iron Leash in the buff.The application is unusual, butfunctional. With the component valuesspecified, the circuit should be used witha soldering iron of 25 watts or less (seetext).

job. As you may know, the heat givenoff by a resistive element, such as asoldering iron tip, is equal to its resis-tance times the square of the rms cur-rent. Since the regulator circuit limitsthe maximum current through the sol-dering iron, it limits the rms current andtherefore the heat dissipated by theiron tip.

There are some interesting advan-tages to this scheme: The circuit emitsless RFI than a Triac power -control cir-cuit. To control power output, a Triaccircuit would turn on 120 times a sec-ond and generate harmonics thatcan interfere with delicate test instru-ments or ham -radio equipment. Onthe other hand, the Iron Leash just cur-tails current flow to a set maximum, itdoesn't turn anything on or off so youcan leave your iron hot while testingRF sensitive circuits.

PARTS LIST FOR THEIRON LEASH

SEMICONDUCTORS1!I-TL7x3 high -voltage n:gulator,

integrated circuit1)I -1)4-1N4001 I -amp rect4ing

diode


RI ---4.7-ohm, 1'2 -watt. 5'4 resistorR2-----25-ohm, 2 -watt, wirewound

potentiometerPLI-3-terminal AC power plug with

line cordSI-spsT power switchS01 -3 -terminal AC socketProject case, high -efficiency heat

sink (or case with a metal lid, seetext), heat -sink compound,regulator -mounting hardware(including mica insulator), rubbergrommet, potentiometer knob.solder. wire. etc.

Construction. The circuit for the IronLeash is so simple that it would be sillyto go through the trouble of making aPC board for it, so we decided to gowith point-to-point wiring. We didn'teven use any perfboard; connectionswere twisted together and insulatedwith heat -shrink tubing. The line cordenters the case through a rubbergrommet, and the AC outlet, controlpotentiometer, and on/off switch aremounted in holes drilled in the case.

Choosing a case to house the cir-cuitry should be carefully thought out.

Everything fits inside this small projectcase; the metal lid is being used as aheat sink. Mounting an AC socket to theside of the enclosure allows the IronLeash to be used for more than asoldering -iron temperature control.

We built the unit as a stand-alone de-vice-in other words, it's basically avariable -current outlet. Therefore, thedevice can also be used for things likedimming a low -wattage light bulb-again, it's best if it's 25 watts or less.However, if you feel that you will use itonly for a soldering iron (as will be thecase with most people), you maywant to incorporate a soldering -ironstand and sponge into the case. Youcan even hard wire the iron directly tothe circuit to avoid purchasing an ACsocket. Before we get down to"choosing" a case, let's talk about whyit's best to power a load of 25 watts orless with the parts we've chosen.

Most voltage regulators, unlesscalled upon for extremely light -dutywork, do require heat sinking (youknow, the little metal tab with thescrew hole in it must be secured tosome kind of heat -dissipating materi-al). And regulator heat sinking is amust for the Iron Leash; it would simplyoverheat and either shut down or de-stroy itself after a short time in use.

Knowing that our Iron Leash wouldrequire heat sinking, we found a smallplastic project case that all of theparts could be crammed into-but ithas a metal lid that we used as a heatsink. If it were not for the metal lid, aseparate heat sink would not have fitinto the case. We'll get into how youuse the lid as a heat sink in a moment,but as for why a 25 -watt load is amaximum, this is the reason: The metallid gets too hot for comfort with any-thing over 25 watts.

So, if you can find a similar case thatall of the parts you choose will fit into,then use it. However, keep in mind thatthe metal tab on the regulator is elec-


Eight -ChannelAudio Switcher

Give your present A/V system something that the audio -component manufacturersseem to have overlooked-more audio inputs

The home -entertainment revo-lution of the past few years hasmeant a big improvement in

the selection of what we can listen toand watch in the comfort of our ownhomes. Hi-fi videotapes; stereo televi-sion, surround sound, laser discs, CD's,cassette decks, radio tuners, and rec-ord players or turntables (yes, somepeople still have and use them) haveadded up to a number of audiochoices that were never even dream-ed of 20 years ago.

In fact, until just recently, most man-ufacturers of receivers and amplifiersdidn't seem to notice the changes.They kept designing and manufactur-ing audio equipment with just one orIwo inputs for auxiliary equipment,and we consumers kept buying them.But now, as we play "catch up with theJones'," adding another piece ofequipment here and there, we'refinding that our amplifiers and re-ceivers just can't handle all thechoices.

Although you could rush right outand get new equipment to handlethe problem, that often isn't the mostpractical solution, especially whenthere's nothing else wrong with the oldstuff. That's where the Eight -ChannelAudio Switcher described in this arti-cle comes in. The switcher allows youto choose between eight -different,stereo -audio sources, and feed theselected signal to one pair of stereoinputs on your current receiver or am-plifier, freeing up any additional inputsthat might be present on the unit.

The Heart of the Matter. At theheart of the audio switcher is anLM1037, a dual low -noise, four -chan-nel analog switch. That chip is de-signed to switch between 4 differentstereo audio sources (A, B, C, and D).Figure 1 shows a pinout diagram ofthe LM1037, which, as you can see,has eight input pins (for four stereosources) and two pins for the stereooutput.

Four pins on the LM1037 (16, 18, 1,and 3) control which stereo input istransferred to the output. The desiredinput is selected by placing a high1-i-V) on the appropriate control pin.For example, to listen to source A 12volts would be placed on pin 16, theA -channel input selector. Any audiosource connected to pins 2 and 4 (theA -channel input terminals) would betransferred to the chip's stereo outputat pins 9 and 10. All other input controlpins are kept low (at ground) until theyare selected.

If no inputs are selected and pin 7(mute) is held low, the output is dis-abled. That feature allows the outputsof several LM1037's to be connectedin parallel to increase the number ofavailable inputs. In this project, twoLM1037's are used to provide 8 stereoinputs. Alternately, if pin 7 is left discon-nected and no inputs are selected, amonophonic audio input at pin 12(the optional common input/bias) willbe switched to both output pins. Thatlast option could prove useful for apaging system, but is not used in thisproject.

About the Circuit. Figure 2 shows acomplete schematic diagram of theEight -Channel Audio Switch. Sourceselection is accomplished by pressingmomentary -contact pushbuttonswitch S1. Switch S1 is connected tothe trigger of a 555 oscillator/timer(U1) that's configured as a monosta-ble multivibrator, which generatesone short output pulse for each pressof S1. That pulse turns on LED1 to give avisible indication that the 555 is work-ing correctly. That pulse is also used toclock U2 (a 4017 CMOS divide -by -10counter/divider).

Both LED1 and its associated cur-rent -limiting resistor R3 are optional,

11

17

13

15

15 112

IN 1

IN 2

IN 3

IN 4

IN 1

IN 2

IN 3

IN 4

+V BIAS

}10

LEFTRIGHT OUT

9

INPUTS

LM1037 LEFT OUT -

} RIGHTINPUTS

18INPUT 2 SELECT -16

INPUT 1 SELECT

INPUT 4 SELECT1

INPUT 3 SELECT -

GND MUTE

17114

Fig. I. This block pinout diagram showsthat the LM1037 has eight input pins (forfour stereo sources) and two pins for thestereo output. Four pins on that chip(16, 18, 1, and 3) are used to selectwhich stereo input is transferred to theoutput.

LEDS 2 -LED 9

PL1

117VAC

S2

F1

5A

T1

12.6V

SA"

BR1

1A

50PIV +

+12V

R2R1 100K

10K 2VvC1

^ .0010 S1SELECT0

LED1

of/

5

C2"1"

114,R3

1K

U5

LM7812

2

+12V INPUTS

C24470-1000

C25.1

16

47

R41MEG

U1

5559 U2

T 15

40173

C3

.1

14

13

8

R5O1K

OLED46-4,) LED5

C4) LED6

LED7

if sl\ LED8

'PN LED9

5

J9 J10

LOO QOR

C7%.-- C8 ==

R6

6 7

J11 J12 J13 J14

L i40 R LOOS

C9 C10:=1 C11 = C1- 2

8

R L CD15

J16

C13 C14- C7 -C14+ 1

R7

16

2

R14

R8 R9 R10 R11 R12 R13 R6 -R13100K

17 11511 13

U3LM1037

+i

C4

5 100

14

C5

1

14 9

12

STEREOOUTPUTS

J17 J180 0

10

U4

LM1037

R15 R16 R17

12

R14 -R211 13 17 15 100K

R18 R19 R20

C15 -C22 +MC15 =C16 MC17 -C18 MC19 -C20L6i OR LOD./

J1 = J2 J3 = J4

2

J5 = J6

3

R21

- C21 -C22R

J7 - J8

4

Fig. 2. Input -source selection is accomplished by pressing S'I; a single output pulse isproduced by Ul fbr each press of SI. That pulse is used by U2 to activate one of its tensequential outputs. Those outputs, in turn, inform U3 and U4 which input source is tobe transferred to the output.

and may be left out of the finishedproject without any affect on circuitoperation. The 4017 advances by oneclock pulse each time S1 is pressed,turning on its corresponding output.Pin 9 (corresponding to output 8) of U2is directly connected to its own resetterminal at pin 15. That allows thecounter to count from zero to seven,and then reset to zero on the eighthcount.

Pin 13, the enable input of U2, is tiedto ground to allow the counter to op-erate. Outputs zero through seven areconnected to eight indicator LED'sand the control pins of the twoLM1037's (U3 and U4). When an outputis selected, its LED lights and the corre-sponding control input on the LM1037

is brought high. To illustrate what ishappening, assume that pin 3 of U2 ishigh. LED2 lights and pin 16 of U4 (thechannel 1 enable) is brought high. In-tegrated circuit U4 then switches theaudio signals applied to pin 2 and pin4 to the IC's outputs at pins 9 and 10.

Since none of U3's control pins arehigh and pin 7 is grounded, U3's out-puts are disabled, and only the se-lected audio signal from U4 appearsat the left and right outputs (J17 andJ18). Pin 12 (bias) of both LM1037's aretied together and connected toground via C3, a 100-µF capacitor, toprevent switching thumps when go-ing from the output of one LM1037 toanother.

The LM1037 has extremely high-im-

INPUTSC23100

pedance inputs and low -impedanceoutputs, so interconnection betweenvarious types and brands of equip-ment should not be a problem. That,together with a wide -frequency re-sponse and low distortion, makes itdeal for use with good -quality, home -entertainment systems. The prototypeof the audio switcher has a usablefrequency response of from just a fewhertz to over 100 kHz.

Power for the switcher is providedby a rather simple circuit (see Fig. 2).Since the switcher only draws be-tween 20 and 30 milliamps, a simplecircuit using the popular 7812 or 78L12(a low power version) voltage reg-ulator works quite well.Construction. A printed -circuit pat-

tern for the Eight -Channel AudioSwitcher is shown in Fig. 3. The circuitboard is a little larger than necessaryfor the simple circuitry of the project,but that allows plenty of maneuveringroom for soldering and drilling mount-ing holes. Unfortunately, due to spacelimitations, that also mean.s that thepattern must be shown here at halfsize.

Figure 4 shows a parts -placementdiagram for the Eight -Channel AudioSwitcher. Note that the printed -circuitboard doesn't contain any of thepower -supply circuitry. Instead, it washard -wired together within the switch-er's enclosure, and connected to theprinted -circuit board at the appropri-ate points.

Begin assembly by installing socketsfor the four IC's, but do not install theIC's in their sockets until the circuit is

T nJ

M.10Ermi

99 9

66

99

a

t 9

(ri

166 6

23/4 INCHES

Fig. 3. Here is a half-size printed -circuitpattern for the switcher. The circuitboard is a little larger than necessaryfor the simple circuitry of the project,but that allows plenty of maneuveringroom for soldering and drillingmounting holes.

PARTS LIST FOR THEEIGHT -CHANNEL AUDIO

SWITCHER

SEMICONDUCTORSU1-555 oscillatoritimer, integrated

circuitU2-4017 decade counter/divider.

integrated circuitU3, U4-LM1037N four -channel

analog -switch, integrated circuitU5--7812 (1 -amp) or 78L12 (100-

mA) 12 -volt, voltage regulator,integrated circuit

BRI-1-amp, 50-PIV, fullwave-bridgerectifier

LED1-LED9-Light-emitting diode

RESISTORS(All resistors are 1/4 -watt, 5% units.)R I -10,000 -ohmR2. R6-R21-100.000-ohmR3, R5 -1000 -ohmR4--l-megohm

CAPACITORSC1 -0.001-µF, ceramic -discC2 -0.01-µF. ceramic -discC3. C25 0.1-1.LE ceramic,

discC4, C23 -100-µF, 35-WVDC,

electrolyticC5-C22-1-).LF, 35-WVDC, tantalum

or metal -filmC24 -1000-µF, electrolytic


F1 -0.5 -amp fuseT1 -12.6 -volt stepdown transformerSI-SPST momentary pushbutton

switchS2-SPST toggle switchPLI-Molded 117 -volt AC power

plug with line cordJ1-J18-RCA jackPrinted -circuit materials, enclosure.

IC sockets, fuse holder. wire,solder, hardware, etc.

completely assembled and checkedfor errors. Although the use of socketsmakes the project a little more ex pe n -sive, they can also save hours of grieflater when trying to remove and re-place defective chips. Jumpers andresistors can be installed next, fol-lowed by the capacitors, taking noteof the polarization of the electrolyticand tantalum units.

Once all of the on -board compo-nents have been installed, place thecircuit board to the side and preparethe enclosure that will house the cir-cuit board and off -board compo-nents. Remember that the enclosure

should have ample room for the cir-cuit board, off -board power supply,and the other off -board components.Drill nine holes in the front panel of theenclosure for the LED's and 2 for theswitches. On the rear panel, drill 18holes for the input/output jacks(J1-J18), and another for the powercord.

Install all of the off -board compo-nents in their respective mountingholes and secure in place. In the caseof the LED's, they can be secured inplace with silicon cement. Begin wir-ing the off -board components(switches, LED's, jacks, etc.) to the cir-cuit board. Although single -conduc-tor hookup wire can be used forconnections between the input andoutput jacks if a metal project box isused, shielded cable will provide bet-ter isolation (less crosstalk betweensources) between the audio chan-nels. When wiring this portion of theproject, it is recommended that youcarefully mark or color -code the ca-bles and then solder them in place.

The final step is to wire the LED's tothe circuit board. There are 8 sepa-rate anode lines for those LED's, corre-sponding to the 8 input channels.One output serves as a commoncathode for all 8 LED's in your finishedproject; simply label the LED's as re-quired. For example, LED2 (input 1)could be tuner. LED3 (input 2) couldbe CD player, etc.

Once all of the parts have beeninstalled and the off -board compo-nents are wired to the circuit board,check your work for the usual con-struction errors. When you are satisfiedthat the circuit contains no con-struction errors, it's time for the smoketest.

Set -Up and Use. Very little has to bedone to set-up the switcher, sincethere is nothing to adjust. As long aseverything has been soldered in theright place, it should work as soon as itis connected in your AN system.

One possible problem that mightcrop up can be traced to the actionof the 4017. The 4017 has a tendencyto allow more than one of its outputsto be on at power -up. If that happens,2 or more LED's will light. To correct thatsituation, simply press S1 several timesto select whichever source you wouldlike to listen to. To avoid the problem,just leave the power to the switcheron.

+12V .4=--C15

-R14-C11115-C17 -R16-

---R17-C18+

C5

J1 J3

LOOLOJ2 J4

R 9R INPUT INPUT $-

1 2

LED20 N(\ /7NZ\

LED4LED5 0 LED6

LED3

U4

C6

J17RIGHTOUT

J18LEFT aOUT 1r

I

J C23

I

C22+---R21- 021-R20-r-R19- C20

+--

J5

C8 - R6--R7-

-R9-+CIO

U3

+C14

-R13-11.2

LED8

R5

f't 1 J J I I IJI ,J

I

J6

NPUT3

J7 J9 J11 J13 J15Lt LOO 9

J8 J10 J12 J14 J16

R *R R OR O0R

s -v -tINPUT INPUT INPUT INPUT INPUT

4 5 6 7 8

Fig. 4. Note that this parts -placement diagram for the Eight -Channel Audio Switcherdoesn't show any of the power -supply circuitry. The power supply was, instead, hard-wired together within the switcher's enclosure, and connected to the printed -circuitboard at the appropriate points.

Here's the author's populated circuit board. It is a little larger than necessary to makeassembly easier.

The author's prototype incorporated two audio-switcher circuit boards and a switchingnetwork.

sl SELECT

C3

ClV.I R2

U2RII

R3

LED1

H4

To connect the switcher to yourequipment, simply plug the outputsfrom your audio sources (CD player,tuner, etc.) into the switcher's eightstereo inputs. Then connect the stereooutputs from the switcher to one inputpair on your amplifier/receiver. Any-time you select that amplifier/receiverinput, you'll be able to hear whateverhas been plugged into and selectedon the audio switcher... without havingto change one cable!

Something Different. The authorchose to incorporate two audio-switcher circuit boards into his finalproduct. The output of one of themfeeds his main amplifier. The output ofthe other goes to the input of a cas-sette recorder. That allows him to listento one source, while recording an-other. In addition, a switching networkwas added to decide which output, ifany, was set for equalization. Youmight have some other arrangementin mind.

However you decide to modify thecircuit, it should give you many yearsand countless hours of listening plea-sure.

A"QUICK & DIRTY"

°QUAD

EN k

If you're a student of anten-na design, or the kind ofperson who insists on pre-

cision and good technique nomatter what, well, good foryou, but you'd better stopreading at this point. Youaren't going to like what fol-lows.

On the other hand, if you'rea CB operator or a ham whowants to take advantage ofthe current hotspots on the 10 -or 12 -meter bands, and all youcare about is getting a goodsignal on the air quickly andcheaply, the QuAD Specialmay be just the ticket.

We call it a QUAD not justbecause it's a full -wave loopantenna, but because its "

Quick And Dirty" too. As thename might suggest, this an-tenna won't win any beauty orefficiency contests, but itshould cost less than $15 evenwith all new parts, and youcan have it on the air in a cou-ple of hours with the mostbasic tools. Plus, it can beerected just about anywhereyou could install a vertical, butit requires no ground plane,puts out twice the signal, andis directional.

Gathering Parts. Sound likeit's worth a try? Then start bysurveying your garage to seehow many "antenna compo-nents" you have on hand. Forthe frame you'll need Iwo 1 -inch radiator -hose clamps,four U -bolts, a scrap piece ofplywood about nine -inches

BY MIKE DEUPREE

If you want to get an antenna upquickly, then our design is what

you're looking for.

square, and three 10 -footlengths of PVC water pipe,each a different diameter. I

suggest 1 -inch, 3/4 -inch and 1/2 -inch sizes, but it depends onthe pipe stock you buy. The im-portant thing is that the small-est pipe must slide snugly intothe next -largest; check for agood fit before you buy. As forthe 1 -inch section, which willbe the vertical member, thethin -wall type isn't as strong,but it slips neatly over the ta-pered end of a standard Ra-dio Shack antenna mast,which can be important formounting purposes.

For the antenna itself you'llneed about 40 feet of wire. I

used No. 14 stranded elec-trical wire with polyvinyl insula-tion because it's cheap,strong, and easily available.The exact length of the wiredepends upon the frequencydesign of the antenna. Theformula for the wire length is1005 divided by the frequencyin megahertz.

You will also need a shortlength of 75 -ohm coax tomatch the antenna to a 52 -ohm feedline. The matching -section length should be 246divided by the frequency inmegahertz, multiplied by thevelocity factor of the coax youuse. If the antenna is for a CBbase station and you are usingstandard Radio Shack RG59Ucoax, you'll need 37 feet, 2inches of antenna wire and 6feet, 10 inches of coax.

The Assembly. With a hacksaw, cutIwo slots in a cross configuration (asviewed from the end) at each end ofthe 3/4 -inch pipe, which will allow it tobe "squeezed" a bit. Cut the 1/2 -inchpipe into two 5 -foot lengths. Insert onelength about halfway into each endof the 3/4 -inch pipe, slip a hose clampover each junction and tighten themenough to keep the inner pipes fromslipping.

You have just completed the hori-zontal frame member. You will be join-ing it to the vertical frame member byusing the plywood as a hub, so drillfour pairs of holes in the plywood,configured as shown in Fig. 1, eachlarge enough to permit a leg of a U -bolt to pass through. Using two U -bolts,attach the plywood to the center ofthe horizontal member. Tighten the U -bolts until they're good and snug butaren't deforming the pipe.

Attach the vertical member (thelargest pipe), to the plywood in a sim-ilar manner, but on the other side ofthe board at a 90 -degree angle tothe 3/4 -inch pipe. Fasten it a couple offeet from one end of the pipe, insteadof at the center as you did with thehorizontal member, and leave theseU -bolts loose enough to allow thepipe to slide easily through them.

Feed the antenna wire through thelength of the horizontal member. Drillholes through opposite walls of thevertical member about a quarrer-inch from the top end. Strip a coupleof inches of insulation (if there is any)

Fig. I. The 10 -Meter version of theQuick And Dirty Quad should bemounted on a TV -antenna rotator andtripod. Four pairs of holes should bedrilled in the plywood in thisconfiguration. The spacing and diameterof each pair of holes depends upon theU -bolt chosen to pass through them.

off one end of the antenna wire, run itthrough one hole and twist it arounditself. Do the same with the other endof the wire in the opposing hole. Stripone end of the 75 -ohm coax and fas-ten the center conductor to one endof the antenna wire and the braid tothe other.

You must now secure the connec-tions. That can be done with with au-tomotive -type crimp connectors. Ifyou choose to solder them instead, beextremely careful not to transfer toomuch heat to the PVC pipe. The ma-terial bums readily, and the fumesare toxic.

Attach an RF connector to the otherend of the coax, and fasten the coaxto the vertical member. Use with elec-trical tape, spaced every foot or 18inches, for that.

Mounting. Your antenna is finishedand needs to be mounted. Ideally youmight have an old TV -antenna tripodand rotator left up on the roof from the"Dark Ages" before cable 1V If youaren't that lucky, secure the base ofthe vertical member to the best an-chor you can find, the higher the bet-ter. If you aren't using a rotator, orientthe antenna so it presents its largestarea in the direction favored for re-ception. Attach the feedline to thematching coax.

Now slide the plywood and horizon-tal member down the vertical mem-ber as far as you can without runninginto your mounting apparatus, andtighten the U -bolts to keep it there.Slide the inner sections of the horizon-tal member out by the same distanceon each side until the antenna wire istaut.

As you do that, the bottom memberwill bend upward like a bow, which isnot only okay, but is one of the reasons(there were others) we used PVC pipe.The flexibility of the bottom member,and the ability to change its length bytelescoping the end sections, allowsyou to adjust the tension and, to acertain degree, the shape of the an-tenna to fit your particular circum-stance. You want sufficient tension toretain the shape and keep the wirefrom tangling or going slack, but notso much that it puts a serious strain onany of the components.

When you get it the way you want it,tighten the hose clamps and that's it,you're done.

There isn't much troubleshootingadvice we can give because if youdid it right, your rig should be lookingat an acceptable SWR reading. If thatisn't the case, recheck the lengths ofantenna wire and coax, as well as theconnections.

Incidentally, by its nature few me-chanical aspects of the "QuAD" areinviolable. You could feed it from thebottom or from a corner, turn it upsidedown, or even feed it to an antennatuner with open -wire line instead ofusing coax.

One final note to fans of portable orfield -day operations: Once built, thisantenna quickly breaks down into asmall, light, easily transportable bun-dle. When you get where you're go-ing, tie a length of line (I favor nylonseine cord) to the top, throw the lineover something high, and pull'er up.Attach other lines to each end of thehorizontal member to anchor or"steer" it.

ELECTRONIC FISHING LURE(Continued from page 87)

The battery should be held in placeby the clip. If not, remove the batteryand adjust the bends at points A and Bso that when the battery is slipped intoplace, it "clicks." Once you have thebattery clip working correctly test theassembly. To test it, simply tie it to a stringand spin it around. Make sure there areno breakables or anyone else in theroom. If the battery doesn't fly out,you've made a good clip.

Take a'/2 -inch piece of 1/4 -inch widecellophane tape and wrap around thewire as shown in Fig. 1 at the point la-beled "insulator." Make the wrap sev-eral layers thick. Next wrap the negativeleg of the LED or the micro lamp aroundthe cellophane -tape insulator. Flowsome solder on the windings on theside that contacts the battery. Solderthe other wire to the clip just beyondthe cellophane -tape insulator.

The lamp or LED can be mounted toface in a variety of directions-for ex-ample, pointing directly out away fromthe battery or, perhaps, pointing to-ward the hook end of the lure. Theswitch is the essence of simplicity-athin piece of plastic or film slid betweenthe battery and battery -contact leadof the LED. Cut the plastic or film into astrip about 1/8 -inch wide and an inch ortwo long.

BASS AND TREBLE

BOOSTER CONTROLSBY A. SINGMIN

Add some pizzazz to your low budget audio projects with a true

tone control that'll make them sound better.

pick up any electronics maga-zine and before long you'resure to come across an easy to

build, low parts -count audio amplifier,suitable for use with your turntable,tape deck, or whatever. Typically,once you've connected the projectto the often suggested junk -boxspeaker and managed to generatesome sound out of it, you hear somedismally disappointing tinny audio-nothing at all like the bone -shakingbass and glass -breaking treble fromyour high cost hi-fi system in the livingroom. The simple circuits often pub-lished rarely have more than a vol-ume control. When they do have atone control, it is usually no more thana treble -cut control that merely con-verts the original tinny audio into an

VIN

R1R2

Fig. I. This basic voltage divider formsthe foundation of the bass- and treble -boost circuits. It simply lacks frequency

100 selectivity.

equally disgusting muddy sound.Of course, using a decent speaker

would improve the sound quality, butwhat you also need is a circuit thatprovides Individual bass boost andtreble boost just as you would find ona hi-fi set. The original Baxandall typeof bass/treble control and it's deriva-tives are found everywhere. They gen-erally take the form of a 4 -terminalnetwork (i.e., there's a terminal for theinput, one for the output, one for acommon ground, and a terminal forthe feedback loop). For the morebasic enthusiast, a simpler, easy -to -use circuit that has only three termi-nals (i.e., an input, output, andground) will be described.

The Bass Section. The best way to

R310K

1K

Fig. 2. The frequency dependence of thecapacitor's impedance permits thiscircuit to boost the bass if desired.

describe how the three -terminal cir-cuit works is to split it into its bass- andtreble -boosting portions and handlethem separately.

To help Illustrate the bass -section'soperation, take a look at the basic DCvoltage divider in Fig. 1. You can imag-ine that R1 and R2 are discrete re-sistors, or consider them as two halvesof a volume -control potentiometerwith the wiper positioned betweenthem. As shown, the input voltage (V)is applied across R1 and R2. Let's saythat V, is derived from some pieceof audio gear. The divided output sig-nal is derived from the junction of R1and R2 (or the potentiometer wiper)and is proportional to the ratio ofR2/(R1+ R2). Thus, as the value of R2 isincreased (which is accompanied bya decrease in R1 for the case of apotentiometer), the output -signalvoltage and volume rises.

Taking things a step further, consid-er the simple capacitor. Unlike the re-sistor, it's reactance (or "AC resis-tance") is a function of the frequencyand is fround from:

)(c =1/(27r1C)

where: Xc is the capacitive reactancein ohms, f is the frequency of the ap-plied signal in hertz, and C is the value

of the capacitor in farads. So we cansee that as the frequency increases,the reactance drops. We can takeadvantage of that to make a fre-quency -dependent voltage dividerthat we can use as a tone control.

Let's now look at a bass -boost circuit(see Fig. 2). Consider an AC signal fedto resistor R3 and ground, with the out-put taken across the potentiometerwiper tap. For clarity, the 100k potenti-ometer can be considered to be aseries combination of 2 resistors (R1and R2), as shown. Capacitors C1 andC2 shunt R1 and R2 respectively.

Note the differing values for R3 andR4, and C1 and C2 (we will explain thedifference shortly). The output signalmagnitude is given by:

V = Vin(1 + ((R1//Xc1) + R3)/((R2/)(c2) + R4))

This seemingly cumbersome state-ment is no more than the basic volt-age -divider equation reworked toinclude the capacitors.

Fortunately, you won't have to usethis formula to determine the output

VIN O )C1

.001

C2

01

100K

"R1"

'R2"

you,

Fig. 3. The treble control is similar inprinciple to the bass control, but thecapacitors are placed in series with thepotentiometer.

as a function of frequency and vari-ous ratios of R1 and R2 as that informa-tion is already summarized in Table 1.For example: with R1- 0 and R2 100k

(representing the potentiometer fullyadvanced to one end), the outputvoltage is a maximum (86% of theinput) at the low frequency end (10Hz)and drops to only 9% at the high fre-quency end (100kHz). What thatmeans is that the bass frequenciesare enhanced with the potentiome-ter in this position. As the potentiome-ter is rotated so R1 starts to get largerand R2 starts to decrease, the amountof bass is reduced. Finally at the otherend of the scale, with R1 - - 90k andR2 = 10k, the output is essentially flatwith respect to frequency.

The Treble Control. The treble con-trol (shown in Fig. 3) works in a similarway. The input is applied to C1 and theoutput is taken from a potentiometerwiper. Resistors R1 and R2 make up theIwo halves of the potentiometer.

The output signal is given by:

you, = Vin x(R2 + Xc2)/(R2 + )(c2 + R1 + Xci)

The response of the circuit as a func-tion of frequency is summarized in Ta-ble 2. With R1= 0 and R2 = 100k, thehigh frequency signals are now en-hanced, while the low frequencies re-main nearly the same.

With a few additional components,the two circuits (bass and treble) canbe combined as shown in Fig. 4. It isassumed that the signal sent into the

TABLE 1-BASS BOOST

R1 R2

Percentage Output Across R2

10Hz 100Hz 1kHz 10kHz 100kHz

0 100K 86% 60% 20% 10% 9%

10K 90K 75% 43% 14% 9% 9%

30K 70K 56% 28% 11% 9°/a 9%

50K 50K 40% 21% 10% 9% 90/0

70K 30K 25% 16% 10% 9% 9%

90K 10K 10% 10% 10% 9% 9%

TABLE 2-TREBLE BOOST

R1 R2

Percentage Output Across R2

10Hz 100Hz 1kHz 10kHz 100kHz

0

10K30K50K70K90K

100K90K70K50K30K10K

9%9%

9%9°h9%9%

14%14%12%11%10%9%

42%39%31%24%17%9%

86%78%61%44%27%10%

98%89%69%49%30%10%

Fig. 4. The bass and treble circuits canbe combined to form a two -control tone -adjust circuit, as shown here. Note theadditional AC -coupling capacitor.

network has been AC coupled andcontains no DC component.

If your application requires, you canuse just the treble portion (shown withthe capacitors in series with the po-tentiometer) by itself. However, if youwant to use just the bass -boost circuit(on the left side of the circuit), be sureto AC -couple both the input and out-put terminals.

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102

TV/VCR SWITCH(Continued from page 85)

the outer sheath to circuit ground andthe inner wire to switch S1. Strain reliefsshould be provided for the powercord and the signal cable.

Once the circuit is completely as-sembled, visually check for wiring er-rors, solder bridges, cold solder joints,etc. Clear any problems that you find.Once everything appears okay, youare ready for the smoke test.

Smoke Test. At this point, all of thecomponents except for U3 should bemounted on or connected to the cir-cuit board in a manner that conformsto the schematic diagram in Fig. 1. Donot connect the wiring from the relayto the AC line yet. Check for continuitybetween both of the relay's AC con-tacts and the circuit board's ground.There must be no continuity. If there is,find and correct the problem.

Once all is okay, plug the unit in andcheck for the proper voltages at pin 8(+ 12 volts) and pin 4 ( - 12 volts) ofU3's socket. If the voltages on thosepins are correct, unplug the unit andinstall U3. Reapply power and checkfor proper operation of the relay withS1 in the MANUAL position and S2 in theON position. If that checks out, unplugthe unit, and assuming everything isokay so far, complete the relay's ACwiring. Close up the case and applypower again. With switch S1 in theMANUAL position and S2 in the ONposition, check for 117 volts AC at SO2(the iv outlet).

When the unit has passed all tests,it's ready for use. Plug the VCR and TVinto their respective outlets. Connectthe signal cable to the VCR's base -band video output (video -dubbingjack). Place the VCR in the VCR modeby operating the TVNCR switch. ManyVCR's provide no baseband outputunless they are placed in the VCRmode. The TV should be set to Chan-nel 3 or 4, since the video source se-lected for viewing will be delivered tothe TV (which functions as a monitor)through the RF or antenna input. Nowcheck and verify the operation of thecircuit.

Once the circuit has been verifiedas operational, you are ready to enjoyyour new video accessory, and theconvenience that it provides.

ONE AMP CURRENT INJECTOR(Continued from page 79)

With everything ready, push andhold the current injector's powerswitch. Now adjust the trimmer poten-tiometer (R7) until you read 1.000 ampof current on the multimeter. That's it.You're done. Once you have cali-brated the unit, you can attach thebox lid using four screws.

Some multimeters cannot directlymeasure current or don't have a 2 -amp scale. If this happens to be thecase, you will need to measure thecurrent indirectly with the use of anaccurate resistor of known value. A 0.1to 1 -ohm, 1% precision resistor thatcan handle 1 amp would be ideal.Attach the current injector clips acrossthe calibration resistor. Then, connectthe digital multimeter leads across theresistor. Set the meter to measure volts.With everything connected, pressand hold the power pushbutton onthe top of the unit's box. Note the volt-age reading and adjust the current -control potentiometer (R7) on the cir-cuit board for a voltage readingequal to the resistor value. If all goeswell, the unit is now ready for use.

Unit Operation. With fresh batteriesinstalled, the FET (9i) will dissipate amaximum of 2.5 watts. The transistordissipation will be maximum when theunit is measuring resistances below 0.1ohms. Although you installed a smallheat sink onto the transistor, it couldstill get very hot if the unit is operatedfor longer than a few minutes. I rec-ommend that you use the system onlyin a momentary manner. Connect itup to the resistor to be measured, at-tach your digital multi meter, then takea quick measurement.

With fresh alkaline batteries, youshould be able to make hundreds ofmeasurements before the batterieshave to be replaced. Also, underweak -battery conditions the powerLED may turn on when the unit is notconnected to a resistor but will fail toturn on when a resistor is connected.This is caused by a drop in the batteryvoltage under a loaded condition.The best way to make sure the unit'sbattery is still good is by activating theunit while the two test clips are shortedtogether. If the light fails to turn on,replace the batteries.

TALKING COMPASS(Continued from page 82)

on the chip at once by pointing thecompass north and holding the push-button down all the time. It will play-back all recorded compass direc-tions, in order. Then it will be in anoverflow condition and cannot bepulsed to playback again. If that hap-pens, just turn the power off and thenback on again to reset the circuit.Likewise, should the Talking Compassever quit playing back, it is probably inan overflow condition; as describedpreviously, just turn the power off andthen on and the unit should resumeworking normally once again.

If the battery runs down, the chipwill not record; at that point, it will play-back only, and the recorded mes-sage will eventually sound drawn out.That's a built-in low -battery warningfeature.

Other Uses. Since the Talking Com-pass is capable of recording a full 16seconds of voice communications, itcan also be used as a message cen-ter. To use the unit as a message cen-ter, simply place S3 in the recordmode, and with the unit facing north,press S2 and begin speaking. The unitwill stop recording when S2 is re-leased, or it will automatically shutdown after 16 seconds has elapsedand its memory is full.

After recording your message, resetthe unit by simply turning it off and onagain. Then place S3 in the playbackmode, and with the unit facing north,press S2. Note that in order to recoverthe message, the unit must be facingthe direction in which the messagewas recorded. Of course, the unit cannot be used as a compass that way,but it is a simple matter to re-recordthe compass points later.

You could also record two 8 secondmessages; one with the compass fac-ing north and one with the compassfacing south. Each message is playedagain by pointing the compass in thedirection that the message was re-corded and pressing S2.

As you can see, there are severalways to use the Talking Compass. Youmay want to "can" a few specialphrases for use at an appropriatetime. Don't let it get you in trouble,though!

TINY TUNER(Continued from page 89)

(maximum capacitance), then applya few drops of quick -setting epoxy tothe flat knob, and mount a conven-tional knob, centering it over the flatone. The right knob will fit perfectlyover the capacitor's flat knob. Makesure that the conventional knob is po-sitioned so that its pointer is orientedwhere you want the maximum ca-pacitance position to be. Next, mountS1 and the switch/inductor assemblyto the front panel, and place amatching knob on the shaft of S2 (theinductoriswitch combo), making surethat the zero -inductance position iswhere you want it.

After that, mount J1 and J2 (twoBNC jacks). Those connectors can bemounted at any location on the plas-tic portion of the enclosure. In the au-thor's prototype, the jacks weremounted opposite to the front panel,one on top of the other. Once all ofthe components have beenmounted, it is time to interconnectthem. The physical wiring is shown inFig. 5. Miniature shielded microphonecable should be used to connect thecircuit's input and output to J1 and J2.Make sure the shields of the two coaxcables are connected together (in

CENTER

CONDUCTOR

TO J2

SHIELDING

TO

Fig. S. Once all of the components havebeen mounted to the enclosure, use thisdiagram as an aid is the final wiring ofthe circuit.

the author's unit, that was handledthrough the capacitor's ground termi-nals) and to the shell of the BNC connectors.

While the circuit is very simple andnothing should go wrong, its a goodidea to check your work for wiring er-rors anyway. If all appears okay, yourtuner is complete and you can closeup the enclosure.

Here is the lulls sired Tiny Tuner priorto the seuling of its enclosure. Note that1.1 obscures the rotors' s h itch to which itis mounted.

Conclusion. Now you have an an-tenna tuner for QRP operation that issmall enough to literally fit in yourpocket. The Tiny Tuner can be lett per-manently in the line since it is by-passed when the inductance switch isset to minimum, and the center -offtoggle switch is in the center position.With the inductance set to zero, youcan tune out inductive reactanceswith the variable capacitor. With theswitch set to oft you can tune out ca-pacitive reactances with the tappedinductor. You electrically reverse thetuner by flipping the capacitor switchfrom "I" to "0;" thereby, permitting youto match high or low impedances.And while the power -handling ca-pability is not very high, it is certainlyhigh enough for almost any QRP rigthat you might wish to use.

SOLDERING -IRON(Continued from page 93)

trically part of the circuit, so it must beisolated from the metal lid with a micainsulator. Drill a hole in the lid in aconvenient location, put heat -sinkcompound on both sides of the micainsulator, and secure both the reg-ulator and insulator to the lid with ei-ther a nylon screw or a metal one witha plastic insulator.

If you choose to use a separateheat sink, then you'll have to go with abigger project case. But, it's a goodidea to use a mica insulator even ifyou use a separate heat sink.

One last Ming to keep in mind: Theunit's output increases as the resis-tance of R2 decreases. So wire R2 ac-cordingly for an increasing outputwith a clockwise rotation. Also, be-cause most of the usable range of theunit is in the lower adjustment rangeof R2, try to use a potentiometer of 25ohms or less. Using a higher -value po-tentiometer will result in a very smalladjustment range at the very end ofthe potentiometer's rotation.

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104

WIRE ANTENNAS(Continued from page 69)

The D.E. Zepp will work on a lot ofdifferent bands. For hams, a 15 -meterband D.E. Zepp will work as a Zepp onthat band, a dipole below that band,and a four -lobed or "cloverleaf" an-tenna above the band.

Collinear Franklin Array Antenna.Perhaps the cheapest approach toreal gain is the Collinear Franklin arrayshown in Fig. 4. That antenna extendsthe dipole and D.E. Zepp conceptseven further. It consists of a half -wave-length dipole fed in the center with a4:1 balun and 75 -ohm coaxial cable.At each end of the dipole is a quarter -wavelength phase -reversal stub thatendfeeds another half -wavelengthelement. Each element is a half -wavelength long (L1), and their lengthcan be calculated from the equationgiven back in Fig. 1A The phase rever-sal stubs are a quarter -wavelengthlong (L2), or one-half the length cal-culated for L1.

The version of the Collinear shownin Fig. 4 has a gain of about 3 dB. Thereis no theoretical reason why you can'textend the design indefinitely, butthere is a practical limit set by howmuch wire can be held by your sup-ports, and how much real estate youown. A 4.5 -dB version can be built byadding another half -wavelength sec-tion at each end, with an interveningquarter -wavelength phase -reversalstub in between. Once you get longerthan five half -wavelengths, whichprovides the 4.5 -dB gain, the size be-comes a bother.

Lazy -H Antenna. The Lazy -H anten-na (shown in Fig. 5) is called a"stacked" antenna because it consistsof Iwo antennas, one on top of an-other. That antenna provides gains ashigh as 5.5 to 6 dB just because of itsconfiguration. In addition, the angleof radiation is lower, so it can put the"first hop" of a shortwave transmissiona lot further out than a simple dipoleantenna.

The phase -reversal harness be-tween the elements should be madefrom either 450 -ohm parallel trans-mission line, or 450 -ohm twin -lead.Note that it is twisted over on itself inorder to make the phase reversal

Li

DIRECTIONOF

TRANSMISSION

DRIVENELEMENT

DIRECTORL3=0.94L1

FEED POINT

TWIST

300aTWINLEAD

L2

A

FEED POINT

Fig. 6. The ZL-special antenna is sort -ofa folded dipole version of the lazy -Hantenna shown back in Fig. 5. However,it does not have a discreet matchingsection.

FOR FURTHER READING

ARRL Antenna Handbook(multiple edi-tions), American Radio Relay League.

Wire Antennas For Radio Amateurs, WilliamI. Orr, W6SAI Radio Publications, Inc.

Radio Handbook -23rd Edition, William I.Orr, W6SAI, editor. Howard W. Sams & Co.,Inc. (Carmel, IN), Cat. No. 22424.

Practical Antenna Handbook, Joseph J.Carr, TAB Books, Inc., (Blue Ridge Summit,PA, 17294-0850; 1-800-233-1128), Cat. No.3270., $21.95 paperback, 439 pages.

happen (lack of this phase reversal isone reason why this antenna mayseem to 'fair when built). The match-ing section (with length L3) should alsobe made of 450 -ohm line.

The 75 -ohm coaxial -cable trans-mission line should be connected topoints "A" and "B" through a 1:1 baluntransformer. These points are foundexperimentally by moving the balunconnection points up and downalong the stub until a 1:1 SWR isachieved. The formulas for the lengthsof the elements (L1), their spacing (L2),and the matching section (L3) areshown in the figure.

ZL.Special Antenna. Figure 6 showsa ZL-Special antenna. It is a half -wavelength horizontal antenna (seenfrom above in Fig. 6). It consists of twofolded -dipole elements built of 300 -ohm television twin -lead wire cou-pled with a 135 -degree phase -rever-sal harness (also made of 300 -ohmtwin -lead). The length of the drivenelement is found from the equationback in Fig. 1, while the director ele-ment length (L3) is about 6% less thanL1. The equation for the length of thephasing harness (L2), which is also thespacing between elements, is thesame as that for the double -extendedZepp antenna (look back at Fig. 3).The feedpoint impedance is about100 ohms, so it is a reasonable (but notexact) match for 75 -ohm coaxial ca-ble. Alternatively, either a 2:1 broad-band impedance transformer, or aquarter -wavelength matching sec-tion similar to the Lazy -H antenna canbe added.

The selection of antennas hereshould give you plenty of ideas to ex-periment with. If you build them safelyand wisely, they should perform verywell.

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106

PORCH -LIGHT CONTROL(Continued from page 65)

Since the Triac is one of the tallestcomponents in the circuit you willhave to alter it to reduce its profile. Todo so, file -down the upper 'far partof each of its terminals. That will allowthe terminals to slide all the waythrough the PC -board holes so thebottom of the part will rest on the cir-cuit board. The filing must be donewith care so that the legs are notmade so thin that they break. Increas-ing the size of the holes instead offiling the terminals is not recom-mended as it increases the likelihoodof forming a solder bridge betweenterminals, (which is especially dan-gerous for pins 1 and 2, which carryAC Dower).

It is strongly recommended that ICsockets be used for both IC's. Thatmeans you'll have to turn an 8 -pin ICsocket into a 6 -pin socket to accom-modate the optocoupler. To do that,carefully cut -down an 8 -pin socket.

Stuffing the Board. Using Fig. 3 as aguide you can begin filling the board.The order in which you place the partson the board is not important, how-ever you should not install the switchor the IC's yet. In fact, keep the 4020 ICin its package until you are ready toinstall it to avoid static damage.

Furthermore, do not solder the po-larized components to the board untilyou double-check their orientation. Inthis circuit none of them will be forgiv-ing if power is improperly applied; it isnot a question of whether there will bedamage, but rather how much!

Having double-checked their ori-entation, solder all the components inplace leaving the switch for last. Tak-ing care not to over -handle the 4020,place it and the optocoupler in theirsockets. Double check their orienta-tion as well.

If, for some reason, you later need totake the switch out of its bracket afterit is soldered in place, it can be donewithout unsoldering by very carefullyunscrewing the last section of thebase of the switch, being ultra -carefulnot to lose the two small springs andcontact plate from inside the body ofthe switch as you do so.

The last step is to install the 8-32screws back into the nuts soldered to

the board. The screws should be inser-ted from the foil side of the board andsecured loosely.

Testing the Unit. For the rest of thisprocedure keep in mind that much ofthe circuit is hot. Touching any ex-posed contact must be avoided.

Turn the porch light on by using itswall switch. Then remove power fromthe porch -light circuit using the ap-propriate breaker or fuse in the elec-trical entry box.

Now remove the wall switch's frontpanel by taking out the Iwo screws onthe panel's face. Unscrew the two ad-ditional screws that hold the switchand its bracket to the wall box. Care-fully pull the switch bracket with its twoattached wires out of the wall box anduse some kind of test equipment (amultimeter, a neon -bulb, etc.) tocheck that neither screw terminal onthe switch is hot. If everything appearsdead, untighten the screw terminalsto release the two wires.

Hook each wire from the wall boxaround one of the 8-32 screws, plac-ing the hooks in the wire in a clockwisedirection and tighten the screws. Nowstart gently pushing the circuit into thewall box checking to see that there isno possibility of the sides or back ofthe control unit touching any metalpart of the wall box. Some wall boxesare made of plastic and presentfewer dangers. Even so, if there is anypossibility of metal touching metaluse layers of electrical tape to insulatethem from one another. With the cir-cuit in place, screw the switch bracketto the switch box. Restore power to theporch light circuit via the fuse or circuitbreaker in the entry box.

The bulb may very well light imme-diately and if it does, it should ex-tinguish after about 21/4 minutes (orwhatever time delay you have se-lected). If it does not immediately light(or after it has first gone out), press thepush button and the bulb should lightand stay lit for the delay period se-lected. Any failure of the circuit boardwill either leave the light on perma-nently, (similar to the spring of theswitch having broken with the switchclosed); or permanently off.

Fit the new front panel in place (re-moving the button if necessary) andscrew it to the bracket. Press the but-ton onto the switch shaft, and you'reall done.

49-MHZ FM TRANSMITTER(Continued from page 54)

whip antennas are chrome platedand therefore do not readily acceptsolder. The mounting hardwaremakes it a lot easier to attach a leadwire to the antenna. Once all of thecomponents have been installed orconnected to the circuit board,check your work for accuracy. If allappears okay, move on to the testand adjustment phase of the con-struction.

Test and Adjustment. Before usingthe 49 -MHz FM Transmitter, you mustadjust R10, L1, T1, and T2. The tuning -core setting for L2 as supplied by the

SPECIAL COMPONENTSOURCES

Toko InductorsDigi-Key Corporation701 Brooks Ave. SouthThief River Falls, MN 56701-0677Tel 800-344-5439

Varactor Tuning Diode (Motorola)Circuit SpecialistsP.O. Box 3047Scottsdale, AZ 85271-3047Tel. 800-528-1417

49.890 MHz Crystal (may be used at16.630 MHz)Jameco Electronics1355 Shoreway Rd.Belmont, CA 94002Tel. 800-831-4242

2SC1687 NPN RF TransistorMCM Electronics858 E. Congress Park Dr.Centerville, OH 45459-4072Tel. 800-543-4330

CRYSTAL SOURCES

International Crystal Manufacturing Co Inc.PO. Box 26330729 W. SheridanOklahoma City, OK 73126-0330Tel: 800-426-9825Fax: 800-322-9426

Jan Crystals2341 Crystal Dr.PO. Box 06017Fort Myers, FL 33906-6017Tel: 800-526-9825Fax: 813-936-3750

Crystek Crystals Corp.1000 Crystal Dr.FT. Myers, FL 33907Tel: 813-936-2109Fax: 813-939-4226

factory is satisfactory and should notrequire adjustment. When adjustingany of the Toko coils (L1, T1, and T2), usea 3/64 -inch blade, non-metallic align-ment tool or, as a last resort, a jeweler'sscrewdriver. The cores are very brittleand fit snugly. Because of that, it is wiseto avoid any unnecessary adjust-ments.

Initially, set R10 to about the 2 -o'clock position. Fully extend the tele-scoping antenna, connect a 9 -voltbattery to the circuit, and press S1.Then, using a DC voltmeter, check for3 volts at the R12/R13 junction; If thevoltage is otherwise, the oscillatormay not tune to the crystal's frequen-cy. The core of inductor L1 may beadjusted to fine tune the oscillator'sfrequency. Generally, however, that isnot required.

The cores of RF transformers T1 andT2 should be adjusted for maximumRF-output power. That is indicated bya dip in the DC emitter voltage, or apeak in reception range. As an alter-native, you can lightly couple theprobe of a 50- or 100 -MHz os-cilloscope to the antenna, and thentune T1 and T2 for maximum signalstrength. Once the adjustments arecompleted, your transmitter is readyfor operation.

Conclusion. The 49 -MHz FM Transmit-ter offers many advantages overother 49 -MHz transmitters and wire-less microphones. Its highly stableVCXO keeps its signal locked on fre-quency. It's easy construction and lowcost allow you to build as many trans-mitters you need to operate on thefrequencies that are of interest to you.And the 9 -volt power requirement al-lows you to use a battery or a 9 -voltwall adapter. In addition, the 49 -MHzFM Transmitter is just plain fun to buildand use, offering insight into the worldof RF circuits.

FREQUENCY COUNTER(Continued from page 50)

pins 29, 34, and 35 of U8 to be surethey are tied to ground.

When the display properly indi-cates all zeros with no input to thecounter, apply a signal to the inputand note the display response on allranges. Use an audio or RF oscillator,or function generator if available. Anywave shape is fine; the amplitude ofthe signal should be at least 0.5 -voltrms, but not more than 5 volts.

Set the oscillator to about 1.9 MHzand check the frequency on the high-est range of the counter; it shouldread close to 1900.0 kHz. Set the fre-quency to 190 kHz and switch the unitto the 200 -kHz range. The displayshould read about 190.00 kHz. Finally,set the oscillator to 19 kHz and coun-ter's range switch to 20 kHz. The coun-ter should read about 19000 Hz.

If the counter does not give theproper indication, use an os-cilloscope to locate the fault. Firstcheck pin 11 of U3 -d for 3.2768 MHz at5 -volts peak -to -peak. If the signal isabsent, check the wiring and compo-nents associated with U3 -c and U3 -d.Try a new ICif possible. Check U1 pin 3for the presence of the trigger pulseon the two highest ranges of thecounter. There should be a 7 -millise-cond wide, negative -going pulse, re-peating about once every halfsecond. When the range switch of thecounter is set to the 20 -kHz position,the pulsewidth triples, and repeatsevery 2 seconds. The absence of atrigger pulse indicates a problem withU1 and its associated components.Check R3, R4, R6, R7, C3, C4, and Q1for proper values and orientation.

Check pin 4 of U3 -b for a periodic10-, 100-, and 1000 -millisecond,positive -going gate signal for each ofthe positions of the range switch. Theabsence of that pulse could becaused by a failure of the flip-flop (U3 -a and U3 -b), U6, U4, or U5. The decadedividers can easily be checked by ob-serving the wave shapes at pins 6 and14 of U6-a rectangular wave shapeat a frequency of 327.68 and 32.768kHz, respectively is normal.

The binary divider can be checkedby observing any of the 12 output ter-minals of U4, and pins 9, 7, and 6 of U5.Each succeeding output terminal

should produce a squarewave of halfthe frequency of the previous stage. Ifthe binary dividers are not operating,and there is a clock signal present atpin 10 of U4, the fault may be with thelatch circuit. In order for the binarydividers to count, the logic level at pin11 of U4 and U5 must be zero for aperiod of 10, 100, or 1000 millisecondsafter each trigger pulse from U1.

The operation of U8 should bechecked by examining the input sig-nals at pins 31, 32, and 33 of U8. At pin32, the amplified signal -generatorsignal should appear as a 5 -voltpeak -to -peak waveform. Pin 31should exhibit the positive -going gatesignal generated by U3 -b at pin 4. Pin33 should have a narrow, negative -going (5 microseconds), differenti-ated pulse.

The absence of a waveform at pin32 of U8 indicates that the analogamplifier is defective. Check the ori-entation of Q2 and Q3 carefully, andbe sure that they are not inter-changed. Check all the parts associ-ated with those transistors to be surethey are of the correct values. Alsocheck the orientation of C8.

Using the Counter. The operation ofthe frequency counter is simple. Theonly operating control is the frequen-cy -range switch, which allows full-scale readings of 19,999 Hz, 199.9 kHz,and 1999.9 kHz. Note that the resolu-tion of the counter for the ranges is 1,10, and 100 Hz, respectively.

The circuit is not sensitive to the levelof input voltage or wave shape, but itshould be within the range of about0.5- to 5 -volts rms. The circuit is usableat frequencies of 10 Hz to 2 MHz, butthe counter will respond to frequen-cies somewhat outside that range.

The counter's 1 -Hz resolution on the20 -kHz range can be exploited onhigher frequencies by taking advan-tage of the overflow characteristic ofthe counter. That feature permits the1 -second gate time of the 20 -kHzrange to be used to indicate the last 4digits of the frequency even thoughthe first digit, 1, is not a valid digit onoverflow.

The circuit draws about 7 milliam-peres, which allows in excess of 20hours use from a fresh alkaline battery.At the end of battery life, the displaywill become dim and/or the frequen-cy count will become erratic. 107

CONTINUITY TESTER(Continued from page 91)

to pay attention to the orientation ofthe semiconductors; and pay par-ticular attention to battery polaritywhen connecting the power source.Connecting the battery with reversedpolarity can destroy the semiconduc-tors.

A small battery holder fashionedfrom a 13/4- x 2 -inch strip of scrap sheetmetal (bent to conform to the battery'sbody) was used to hold the battery tothe board between the two IC's. A com-mercially available battery holder willalso fit that area. A homebrew holderwas used because the sheet metal wasavailable, and to help keep costsdown.

Although the author chose not to doso, the circuit can be housed in anysuitably sized enclosure. The enclosurewill require at least eight holes; seven inthe top for the LED's and one in the side,through which to feed the test leads.Note: If the circuit is to be placed in an

enclosure, it will be necessary to eithermove the battery or the LED's off -boardto allow the LED's to protrude throughthe case. (I'd opt for moving the battery,since doing so involves adding no wireleads to the board).

If you decide to mount a battery holder onthe board, care should be taken so as notto sever or short the circuit -board traces.In the case of the latter, it may benecessary to use insulating washers on thefoil side of the board.

The test leads can be terminated inthe test terminal of your choice: probe

tips, alligator clips, hook clips (which theauthor used for his prototype), etc.

Test and Operation. To check thecontinuity tester, insert a 9 -volt batteryin the battery clip. Touch the two testprobes together. The LED's should flashvery rapidly. When the test points areopened, the LED's should extinguish. Aswas noted earlier, the rate at which theLED's flash is proportional to the resis-tance between the two test points.

As mentioned, the continuity testeralso gives a relative indication of theresistance between its probes. For ex-ample, if a resistance of 330k is con-nected between the test probes, LED3will flash at a 2 Hz rate, while all othersflash at a rate that's either faster or slow-er than 2 Hz. With a little practice it iseasy to judge the 2 -Hz flash rate.

The tester can be used to test semi-conductor junctions and other compo-nents. A forward -biased silicon junctionwill cause LED5 to flash at 2 Hz. No LED'swill flash when the test points are con-nected to a reverse biased junction(effectively an open circuit).

NEGATIVE ION GENERATOR(Continued from page 14)

In passing, if you chose not to buy D1from the supplier mentioned in theParts List an exact replacement may bedifficult to locate. However, eventhough it has a lower current rating, anECG -518 should work fine, although thissubstitution has not been tried.

The discharge point should be"pointy" to enhance the ionization ofthe air. You can use a sewing needle, forexample. An alternate discharge point

mcan be fashioned from a small piece of

zro No. 22 stranded wire. Strip off about'

i inch from one end of the wire and sep-arate the fine copper strands so that

1(7) they are more or less evenly dispersed.When the wire is connected to the high

coCI3 negative voltage, the end of each

strand will behave as a discharge point.cr)O You can use any enclosure largeE enough to hold all the components. I'd(I recommend using a plastic enclosure ifO one is available. You should place a fewEj air holes in the side or bottom of yourc') enclosure for the fan to draw air in. TheF2 fan should be situated in the enclosure

108 to pull air in past the discharge point(s)

As you can see, there is some space left between components. Note that in the prototypetwo capcitors have been used to emulate CI.

and out through an opening hole atthe top of the enclosure.

Any screen or covering on the fan -outlet hole should be non-metallic orplastic in nature. Using a metal screenwould severely cut the efficiency of thegenerator because the negative ionsthat come into contact with the metalscreen would be neutralized.

When testing the circuit, if you see

any arcing or discharge from the highvoltage transformer or high voltage ca-pacitors, cut the power immediately.Let the project sit for awhile to let thecapacitors discharge, and, withouttouching the project if possible, coatthe faulty area with a little "No Arc"spray (available from Radio Shack). Al-low the material to dry before testingthe unit again.

TRACKING TRANSMITTER(Continued from page 24)

spread. Spreading the windings willalter the inductance of the coil, thuschanging the frequency range of thetransmitter. That could make it impos-sible to tune in the designed FM range.

Once all of the on -board compo-nents have been mounted, connectthe antenna. The antenna is nothingmore than a 12 -inch length of #22stranded insulated hook-up wire. Atthis point, connect a 9 -volt batterysnap to the circuit. If you wish, you canadd an on/off switch to the circuit byconnecting the switch in series withone of the battery leads.

Although the Tracking Transmitter isdesigned to be used without a chassisbox, you can house the unit in a smallplastic or metal box (recommended ifyou will be including an on/off switchin the circuit). A metal box is the pre-ferred enclosure; it will make the trans-mitted frequency much more stableand easier to set.

Checkout. Check over your work forproper assembly and short circuits.Make sure that each transistor is cor-rectly oriented and in its proper place.Check each resistor and make surethe resistor values are in the properlocation as well. Connect a 9 -volt bat-tery to the circuit.

Use an oscilloscope to look at thesignal at the collector of Q2. Youshould see a pulse train with a peak -to -peak amplitude of approximately8 volts. The positive -going pulsesshould be approximately 300 -millise-conds wide and should be separatedby approximately 1500 -millisecondspaces. If you don't have an os-cilloscope, connect the ground leadof an analog (non -digital) voltmeterto the negative terminal of the bat-tery. Set the voltmeter for 10 volts orhigher. Connect the positive lead ofthe voltmeter to the collector of Q2.The meter reading should repeatedlypulse from about 1 to about 9 volts.

Next, turn on an FM receiver and set itto c clear (unused) frequency between88 and 108 MHz. Using a non-con-ductive alignment tool adjust C7 andC6 until you hear the transmitter on thereceiver. You may have to squeeze orspread L2 to insure that the TrackingTransmitter tunes from the low end tothe high end of the band.

RING LAUNCHER(Continued from page 34)

ground the AC line voltage to a met-al chassis. In addition, an isolationtransformer should be used whentesting or troubleshooting the cir-cuit to avoid a very serious shockhazard.

Apply power to the circuit; DISP1should display a 9. Press S1 andmonitor the display. The displayshould show a descending count. Ifthe counter does not function (the dis-play fails to count after pressing S1),check for a clock pulse on pin 3 of U5.If U5 is receiving the proper clock sig-nal, check the BCD output wiring thatfeeds U4 (the latch/decoder/displaydriver) for a BCD output at pins 3, 2, 6,and 7 of U3. Confirm that those termi-nals are wired to pins 7, 1, 2, and 6,respectively, of U4. Also check U4 pins5 and 16 for the proper supply volt-age.

The monostable timer (U2) shouldtrigger as soon as the counterreaches zero. A UL logic probe or anoscilloscope can be used to checkthat Q1 pulls pin 2 of U2 low when thecount of zero is reached. About onesecond later, the output of U2 at pin 3should go low, resetting the flip-flop(U1-a/U1-b). Check for a low on pin 11of U3; that disables the counter/dis-play at a count of zero.

If the ring is not repulsed when thecount reaches zero, check to makesure that pin 12 of U3 goes high, trig-gering U6, on the zero count. If that'sokay, check that the gate of TR1 re-ceives a trigger voltage from the op-toisolator/coupler on the zero count. Ifall seems to be okay up to that point,check the interconnections to andfrom the Triac. If the Triac is wired cor-rectly, but the ring is still not repulsed,try replacing the Triac. Continuechecking the individual sub -circuitsuntil the problem is located and cor-rected.

One final note on safety before weconclude: While the prototype doesnot propel the aluminum ring with anygreat force, you should, nonetheless,not point the unit at any person oragainst any object that may beharmed by contact with the ring. Itwould be a shame to ruin the fun thisproject could provide through a care-less act.

HOT CANARIES(Continued from page 30

their sockets, but do not mount theboard in its enclosure yet; it must still betested.

Testing. To test the circuit, place a 9 -

volt transistor -radio battery in the hold-er, attach the snap -on connector to thebattery, and turn S1 to the on position.You should hear chirping sounds notlong after the circuit is powered up.Using a voltmeter, check the +V inputof each chip at pin 4 for + 9 volts. Onceyou established that the IC's are receiv-ing power, potentiometers R5 and R6must be adjusted.

Once the printed -circuit board has beenattached to the lid -mounted speaker andswitch, it must be tested and adjusted toensure proper operation, prior to beingsealed in its enclosure.

Adjustments to R5 and R6 are bestdone by temporarily desoldering R1and R2 in turn. Remove R1 first and ad-just R6, so that chirping starts at a slowpace then increases to a faster rate,and then stops before starting again. Ifthe trimmer is too far counterclockwise,the canary will hardly chirp at all, but ifit's too far clockwise, it will not stop chir-ping. Once that adjustment is com-plete, reinstall R1, remove R2, andadjust R5 in the same manner. The chir-ping from the second half of the circuitshould sound slightly different from thefirst.

Once the second half of the circuithas been adjusted, the printed -circuitboard can be mounted in the en-closure, and the enclosure can then besealed. As a final touch, you can attacha pair of artificial canaries to the lid ofthe enclosure to partially conceal thespeaker holes and the switch lever inthe lid.

109

VOLTAGE ADAPTER(Continued from page 22)

Put an "S" -shaped kink in the wiresto the switch to allow them to fold overonce they are put in the lighter plug.Now insert the assembly, switch -first,into the lighter plug. As you do so, foldback the wire that goes to the centercontact of the lighter plug. Make surethat the switch's body is perpendicularto the hole for the coax. That allowsthe switch to slide over the coax with-out pinching it. Once the switch is all

TO PL1

TO PL2

across the lighter plug's contacts. Itshould read about 6000 ohms. If youget zero or an off -scale reading,check for an open or short in the cir-cuit, respectively. If all is well, plug theunit into your car's cigarette -lightersocket and measure its output with avoltmeter. Unless you've redesignedthe unit for different outputs, with theswitch in the center position, the de-vice should yield 9 volts. The other po-sitions should give 6 and 3 volts.

If you get nothing out, check theground and Vout connections. If youget three incorrect voltages, check

U1

LM317WITHOUTHEATSINK

R4

CUT OFFTAB OF

REGULATOR

Fig. 3. Here is the best way to lay out the parts to form a neat, compact package. Youshould use heat -shrink tubing to insulate all the connections.

The inside of the Car -Power Adapter is laid out like this. As you can tell, the compactdesign requires precise lead lengths to fit properly in the plug.

the way in, turn it to align it with thecoax. Push the clip the rest of the wayin and screw on the cap containingthe center contact.

The plug you connect at the far endof the power cord (PL2) and its polar-ity is up to you. I chose to use an RCAphono plug because I have a fewadapters that can convert it for usewith the devices I have. Once youhave connected PL2 you're all done.

Testing. Before plugging the unit into

110your car, take a resistance reading

the connections to R1 and R2. If themaximum voltage (9 volts for the au-thors model) is correct, but one orboth of the other voltages are wrong,check R3 and/or R4 as necessary.

Once ready, your Car -Power Adapt-er should bring you many hours of lis-tening pleasure. As you'll probablydiscover, it can be used for more thanjust audio and is perfect for working ona laptop by the shore, or to give your-self a quick shave before an importantappointment. You're bound to comeup with more uses on your own.

TUNE PIANOS(Continued from page 20)

the piano is less than a semitone belowstandard pitch, then bring it up by 20cents. Never bring a piano down inpitch, always up.

You may have noticed the slight dis-crepancy between the value that wecalculated for middle C and the valuelisted in Table 1. As indicated in the ta-ble, C40 is "stretched" downward by 2cents. The reason for that is that be-cause of their stiffness, steel strings gen-erate overtones that are slightly higherthan true harmonics. That makes an oc-tave sound flat, unless it is stretched tocompensate. The pitches shown in Ta-ble 1 are stretched for the averagepiano tuned to standard pitch, whichwill produce excellent results for anypiano.

To include the - 20 stretch in our pre-vious calculation of C40, the exponentof 2 would have been 902/1200. For anypitch other than standard, you'll have tocalculate and tabulate a new table ofpitches. That's an involved and tedioustask. Fortunately, there is an easier ap-proach: A computer program for thePC, available from the vendor namedin the Parts List, will do the work for youand print the results. It calculates thepitches for all 88 keys for any value ofA49, and can optimize the stretch forthe type of piano, whether spinet, up-right, or grand. It can also generatetables of unstretched values.

When tuning the strings in sequence,it's best to start with key 1 and work yourway up the keyboard to key 88. The top -octave strings do not sustain well, andmay present some difficulty in readingtheir waveforms on the scope. The ster-eo headphones can be used here togive an audible indication of relativepitch. They are also useful when tuningin a noisy environment, which can dis-rupt the waveform display. It is possible,with practice, to tune the entire pianowithout the microphone and os-cilloscope; that is done by listening tothe tone in the headphones whilecarefully adjusting each string of theinstrument for zero -beat.

If you use the Precision Audio -Fre-quency Generator to tune an organ orother non -stringed instrument, nostretch should be used. The pitches canbe calculated from the formula given inthis article.

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112

TELEPHONE RING CONVERTER(Continued from page 56)

Testing and Operation. Start by re-checking your wiring to make sure youhaven't made any errors. When youare confident that everything is okay,you can check out the ring converterby using the 60 -Hz signal present onyour home's powerlines. To do that youwill have to take a line cord and add afuse to it to form a test jig as shown inFig. 5. Be sure to use a 14 -amp fast -acting fuse as shown, and Insulateall connections to prevent a shockhazard. Be cautious when workingwith house current-remember:safety first! Once you've modifiedthe line cord, attach it securely to theappropriate points on the circuitboard.

FlI/4 -AMP FAST -ACTING FUSE

PL1

TO GREEN

WIRE TERMINAL

TO RED

WIRE TERMINAL

Fig. 5. A quick test jig can be madefrom a linecord and a fast -acting fuse.as shown here. Be very careful toinsulate all the connections of thisassembly.

Turn both the volume and tone con-trols to mid -position, and plug the as-sembly into a wall outlet. Adjust thevolume and tone controls throughtheir ranges; you should hear the war-ble of the ring converter. If nothing isheard, unplug the assembly andcheck to make sure the fuse hasn'tblown. If it has, check for a wiring errorbefore replacing the fuse.

Make sure the ring converter pass-es this test before connecting it to thephone line. When you are satisfiedwith its performance, disconnect theline -cord/ fuse assembly. Finish theproject by using decals or a labelmaker to provide legends for the con-trols, and fit the circuit into an appro-priate case.

Disable the bell in the telephone byswitching the bell off (look for a slideswitch on the side of the telephonenear the bottom), or move the bellloudness lever to low. Another way to

PARTS LIST FOR THETELEPHONE RING

CONVERTER

RESISTORS(All fixed resistors are 1/4 -watt, 5%

units.)R1 -2200 -ohmR2-1-megohm, linear -taper

potentiometerR3-l-megohmR4 -100,000 -ohm, linear -taper

potentiometer

CAPACITORS400-WVDC, Mylar

C6-10-11F100-WVDC non -polarized electrolytic


Ul-TCM1506 Texas Instrumentsring-detector/driver, integratedcircuit

BZ1-25,000-pF piezo transducerclement

Modular telephone extension cord(see text for type), project box,potentiometer knobs, circuit -boardmaterials, wire, solder, etc.

mute a mechanical bell is by wrap-ping the bell rim(s) with electricaltape. The tape will dampen the bellring to a whisper.

To use the Ring Converter simplyplug the jack into a modular wallsocket as shown in either Fig 4A or Fig.4B. Call up a friend and ask them tocall you back and let the phone ring.Adjust the tone and volume to apleasant level and you are done. Youwill find the Ring Converter indispen-sable if you work in an office area fullof ringing telephones.

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High Energy Capacity ChargingHVM7 Plans Complete System $15.00HVM7K Complete System KiVPlans $174.50TCL4K Tesla Coil Only Kit/Plans $99.50115/19AC Wall Adapter for 115AC $15.50

Table Top Tesla CoilSpectacular -A Real Attention Getter! 250,000 Volts! 7-10' Sparks!Energy even passes throughwindows. Great for scienceprojects, displays, advertising.

Highly spectacular devices producesvisible, audible bolts of lightningappearing to flash in the air. Causescertain materials to burn from within and glow, lightsbulbs without wires, produces induction fields, St Elmo'sfire corona. Clearly demonstrates high frequency highvoltages yet terminal may be touched by user duringoperation with a metal object. 115VAC operation only.BTC3 Plans .. $15.00 BTC3K Kit/Plans $299.50BTC30 Assembled and Tested $399.50

Shocker Force Field / VehicleElectrifier - Neat little device allows you to makehand and shock balls, shock wands and electrify objects,charge capacitors. Great pay back for those wise guyswho have wronged you!SHK1KM Easy To Assemble Electronic Kit . $24.50

Ultrasonic BlasterLaboratory source of acousticalshock waves. Blow holes inmetal, produce "cold" steam,atomize liquids. Many cleaninguses for PC boards, jewelry,

( coins, small parts, etc.$10.00 ULB1K Kit/Plans $6950

100,000V Intimidator / Shock WandModule Build an electrical device that is affectiveup to 20 feet. May be enclosed for handheld, portablefield or laboratory applications.ITM2KM Easy to Assemble Electronic Kit ... $49.50ITM2 Plans Only; Credit -able to Kit $10.00

Ion Ray Gun - Projects charged ions that induceshocks in people & objects without any connection!Great science project as well as a high tech party prank.

10G3 Plans $10.00 10G3K KiVPIans $69.50

Invisible PainField GeneratorShirt pocket size electronicdevice produces time variantcomplex shock waves of intense directional acousticenergy capable of warding off aggressive animals, etc.IPG7 Plans .... $8.00 IPG7K Kit / Plans $49.50IPG70 Assembled $74.50

Homing / Tracking Transmitter -Beeper device, 3 mile range.HOD1 Plans .... $10.00 HOD1K KiVPIans $49.50

Listen Thru Walls, FloorsHighly sensitive stethoscope mike.STETH1 Plans ... $8.00 STETH1K Kit/Plans $44.50

3 Mile FM WirelessMike - Subminiature!Crystal clear, ultra -sensitivepickup transmits voices and soundsto FM radio. Excellent security system, warns ofintrusion. Become your neighborhood disk jockey!Monitor children and invalids.FMV1 Plans $7.00 FMV1K Kit/Plans . $39.50

Telephone Transmitter - 3 Miles!Automatically transmits both sides of a telephoneconversation to an FM radio. Tunable Frequency Undetectable on Phone Easy to Build & Use Up to 3 Mile Range Only transmits during phone useVWPM7 Plans .... $7.00 VWPM7K KIVPIans $39.50

INFORMATION UNLIMITEDDept PEM12, Box 716, Amherst, NH 03031Phone: 603-673-4730 FAX 603-672-5406MC, VISA, COD, Checks Accepted. Please Add $5.00 Shipping & Handling

with many mono Items

FREE with Order,Or Send $1 P&H

PlasmaFire Saber

Produces the spectacular effect that captured the fantasyof millions of movie fans. Visible plasma field iscontrolled by grip pressure and adjusts saber length.Active energy field produces weird & bizarre effects.Excellent for special effects. Specify photon blue, neonred, phasor green, or starfire purple.PFS2 Plans .... $8.00 PFS2K KIVPIans $49.50Special Offer PFS20 Assembled reg $895°, $59.50

TV & FM Joker / Jammer - Shirt pocketdevice allows you to totally control and remotely disruptTV or radio reception. Great gag to play on family orfriends. Discretion required.EJK1KM Easy to Assemble Electronic Kit $19.50

Visible Beam LaserHigh brightness red HeNe laser visible for miles.Produce your own light show! Projects a beam orred lite clearly visible in most circumstances. Can beused to intimidate by projection of a red dot on targetsubject. Also may be used to "listen in" using ourlaser window bounce method #LLIS1 below. Easyto Build Modules Makes A Working Visible Laser:LAS1KM Kit w/1mw Laser Tube, Class II . $69.50LAS3KM Kit w/2.5mw Laser Tube, Class 111A$99.50

"Laser Bounce" Listener Systemallows you to hear sounds from an area via a lite beamreflected from a window or other similar object. Systemuses our ready -to -use LATR1 Laser Terminator gun siteas the transmitter. The receiver section is supplied asan easy -to -build kit, including our cushioned HS10headsets. Order # LLIST20 System, includes ourLATR1 Ready -to -Use Laser Gun Site, LLRIK SpecialReceiver Kit, and HS10 Headset, all for only $299.50

5mw Visible Red Pocket LaserUtilizes our touch power control!VRL3KMX Kit / Plans $119.50

See In The Dark ViewingDevice uses invisible infraredillumination for seeing in totaldarkness. Excellentfor low cost nightvision,along with observinglasers and other IR sources.Functional unit, many useful applications.SD5 Plans . $10.00SD5K Kit / Tube / Plans $299.50GPV10 Ready to Use Viewer $499.506032A Tube / Plans to build your own ... $99.50

Order by Mail,or by 24 Hour

Orders -Only Phone:

800-221-1705

(800) 645-9212KELVIN (516) 756-1750Imimglimlimumil10 HUB DRIVE, MELVILLE, NY 11747 (516) 756-1763FAX

100 Basic 150 Basic+ 200 Advanced PRO 400Standard Features - Models 100, 150, 200 & 400 AC & DC VOLTAGES DC CURRENT RESISTANCE CONTINUITY TEST -Buzzer DIODE TEST 3 1/2 DIV LCD LOW BATTERYINDICATOR ACCURACY +/- 0.5% RDGBATTERY TEST TRANSISTOR 20MHzFRECIKELVIN CAPACITANCE COUNTER

990087 Aux AC/OCCURRENT100 Basic CURRENT CAPACITANCE

$ 1 9 9 5 1#790V019/4

LOGIC TEST1 'TRANSISTOR

-TRANSISTOR 200 Advanced LED TEST

VERIFY GO OCVRADBATTERY TEST KELVINKELVIN *990092# 990090

PRO 400150 BaS1C+ 30 DAYMONEY

6995$2995 BACK

2 Year Warranty (Parts & Labor)

KELVIN 94 The Ultimate MeterLCR - Hz - dBm - True RMS - Lo is ProbeThe only meter with 0.1% Accuarcy on DCVoltages, built-in True RMS, Frey Counterto 20MHz Res: 10 Hz, LCR-InductanceTester Res: 10 uH, DC/AC VoltagesRes.0.1mV, Ohm Meter Res: 0.1 ohms

12 INSTRUMENTS IN ONE -AC & DC VOLTMETERS,AC & DC CURRENT, dBm,OHMMETER, DIODE TESTER,AUDIBLE CONTINUITY TEST,20 MHz FRED COUNTER,CAPACITANCE METER,INDUCTANCE METER,LOGIC PROBE

TRUE RMS PLUS

Model 94#990111

$19995

ENGINEANALYZER PLUSModel 95 #990112

$19995

DIGITAL TRAINER

Laptop POW Trainer comes oUr 100 pagertstucton manual, power supply. Cult in 1

doe tue he xadearnel dospl ay two rdependentdocks rah user adrostable Seto 8 duty cyder.4 data to switches and 4 LED clupays

Stock No. 1540460 99"COMMUNICATION TRAINERWIRE - FIBER OPTIC - INFRARED

Ideal for schools,Explore the technology of communicoOons withWIRE, FIBER OPTIC 8 INFRARED; one selcpwhich Incorporates 3 technologresStock No. 840515 /ACT '275

BREADBOARDS

5.61EL A O Oe

Stools No. Post Contacts YOURGOAT

680093 0 500 s 4.25680097 0 840680098 2 1380680100 4 2390WIRE JUMPER KITR. -cut, Pm -Stripped330289 140 Piece Sel ....$ 4."330290 350 Piece Set 8."

611.'5:22.05

WALL TRANSFORMERSWALL TRANSFORMERBATTERYELIMINATORCENTER NEGATIVE!TOO( NO TYPE Geom.

220084 90 DC300 rwA220068 IV DC/500 teAMALE JACKST005 PO TYPE

370048 2.1 mm Male$ 49 e. $.39 rla.

TEST ACCESSORES

Standard Features plus -TEMP, TACHOMETERDWELL ANGLE TESTER,DUTY CYCLE, 10M OHMIMPEDANCE, ANALOG BARGRAPH, K -TYPE TEMPPROBE, ALLIGATOR CLIPTEST LEADS, INDUCTIVEPICKUP CLIP, 6' TEST LEADS

DELUXE CARRYING CASEStandard Features - Models 94 & 95 DC/AC VOLTMETERS AC DC CURRENT OHM METER DATA HOLD RELATIVE MODE FRED COUNTER to 4 MHz (Model 95) AUDIBLE CONTINUITY TEST DIODE TEST MAX'MIN AVERAGE MEMORY RECORD 10A HIGH-ENERGY FUSE PROTECTION AUTO SI F FP & AUTO POWER OFF

SCOPEPROBES60 MHz, X1 8 XIO

SPECIAL700072 $18"150 1442, X10

700073 13915

IC CLIPSSOLDER TYPESPRING LOADEDSect No COLOR COST 25. Oty990104 BLACK .65 . I .50 .woos RED .65 .50..

IC TESTLEAD SET5 COLOR CODED ITliEWAYUPE 0005 GM18 LEADS WITH

PROD*, BOVA ENDSStock No. YOUR COST 3. Otyaeoloa '8.95.. $8.25 v.

CIRCLE 18 ON FREE INFORMA

Established 1945

M/C & VISA '20Minimum

KELVIN CATALOG 53Stock No. 650412

TESTINSTRUMENTS

T145 MONTH. SPECIAL I

BONUSRequest Your

-FREE -KELVIN 103Multi meter

will your Scope order

20 MHz SCOPEDual Trace 2 Yr Warranty -Pct. 8 LaborStock No. 740355 '38540 MHz SCOPEDuel Trace with Dateared Sweep2 Yr Warranty-Parts8 LaborStock No 740086 '655100 MHz SCOPE3 Channel, 8 It... with Delayed Sweep2 Yr Warranty -Parts & laborStock No. 740089 31,295

HITACHI - DIGITAL STORAGEMODEL VC -6025 50 MHz SCOPEAUTORANGE_ 20IASS, RS -232 PORT3 Yr Warranty -P. 8 LaborSock No. 100074 *2,595

FLUKE - SCOPEMETERMODEL 97 FULLY LOADEDHANDHELD, 50 Metz, DUAL O4ANNELStock No. 710046 31,795

DISCOUNTED PRICES!FLUKE

AUTHORIZED DEALERFLUKE 79 Soros lI '169FLUKE 87 True RMS $289

FLUKE 45 '599

FLUKE 3 YEAR WARRANTY

2 MHz FUNCTION GENERATOROutput. SINE. TRIANGLE, SOUARE WAVE,PULSE, RAMP SLEWED SINE WAVEStock No. 720098 $199'6

100 MHz MULTIFUNCTION COUNTER8 DIGIT LED DISPLAY ram DECIMAL POINTStock No. 720099 $189'6

150 M147RF SIGNAL GENERATOR1004044 b 1501.4147 COVERAGE450MHz IN HARMONICS, AM MODULATION.IN OR EXTERNAL 0 100%Stock No. 720022 $219

DC POWER SUPPLYCONTINUOUSLY VARIABLE -TWO SEPARATE LED DISPLAYS, GREENREADOUT FOR VOLTAGE 8 RED READOUTFOR CURRENT

sock No 600036... 30V 3A $295so 690039 60V g 1.5A 1295

POWER SUPPLIESwrre ANALOG DISPLAY METERADJUSTABLE OUTPUT VOLTAGE a cusses,

18V / IA Single OutputBeck as 690040 8155

18V 1 1A, 30V / 0.5A Dual Outpul680041 '215

LOGIC PROBESASURES TTL, DTI, RTL. CMOS

Stock No. Model VC", C 3ST740071 LP10A - 17 Wiz '

740087 LP25A - 25 Lei: :;9°'740088 LP50A 50 MHz 149"

LOGIC PULSERSYOTORABLE 0.5.400 PULSE RATE, 100mAStock No. Model YOUR COST

740073 PR41 $4915

COMPONENTSWHOLESALE PRICES!

Pc MtnStock No. TYPE YOUR COST600021 555 TIMER '20600029 556 DUAL TIMER .40 ea

600039 LMSS6 PPL '.60 eaFUNCTION GENERATOR

600018 741C OP -AMP '.30 caINTERNALLY COmPENSATED

600026 1458 OP -AMP '.35 caDUAL 74iC OP AMR

630041 2N2222 '.20 ca

630383 PN2222 q8

600023 7805 Voltage Rep '.36 La

SIUCON CONTROLLED RECTIFIER(Smdar to GE C106G11 4 0 art -17 1 DOPIV600014 ',89 ea '.79 94'10.

THERMISTER 100 ohm110097 '1.35 ea 1.00 ea/20.THERMISTER - 10K ohm110097 '1.35 ea 1.00 ea20.

PROJECT PARTSP rojectSpeaker2-, 8 Ohm, .1 WartStock No. 350009

59

P rojectBUZZER

- 9 Volt DC, 80 ribStock No. 660089'1.59 ea$1.39 ea; 10. Chy

SolderingIRONwith STANDLONG LIFE TIPStock No. 99009813.95 ea

L E DTI3/4Stock No Color 100. oa 1000. Os260020 RED '.05 ea '.045 ea260027 GREEN '.08 ea '.07 ca260026 YELLOW '.08 ea '.07 ca260078 2 COLOR '.32 ea '.29 ca

RE CI GREEN

XENON STROBEStock No. TUBEnoose$2.95 ea$2.50 ea / 20. Oty

TRIGGER COILfor XenonStrobe TubeStock No 320037$1.25 eaI .89 ea 120. ay

INFRARED LEDIR Pair, LED infraredtransmitterand receiverStock No. 260061

11.95 ea

NEON LAMPNE2, 2- LeadStock No. 260303'.15 ea

.12 ea / 100. Oty

PHOTO CELLPhoto Cell - 450 ohmStock No. 260717

s .65 ea :.45 ea 20. OtyPhoto Cell I.56 ohmStock No 260010

1.65 ea 2.45 ea 20. Oty

PUSH-BUTTON SWITCHPUSH -ON, PUS14-OFFStock N. 270021'.55 ea$ .49 ea / 100. thy

SLIB.B'INIATURE MOMENTARY' . ITCH

No. 990002

'.35ea$ .28 ea 1100. OtyMINIATURE TOGGLE SWITCHStock No. 2700341.90 ea Type. SPSs .79 ea / 50. Qty `1".

TION CARD

3ERNSBACK SPECIALTY SERIES Q3 49604 …americanradiohistory.com/Archive-Hobbyist-Specials/...XK-500 Digital / Analog Trainer A complete mini -lab for building, testing, prototyping

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