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THE MAGAZINE FOR THE RADIO & ELECTRONICS EXPERIMENTALIST
July/August 1990 £2.95
36 -PAGE St PPLEMENT OFFERING A VARIETYOF SMALL CONSTRUCTION
PROJECTS
Battery testerSound demodulator bar SAT TV receiversSquare -wave
generatorTTL-level 100 MHz quartz oscillatorSCART-plug FM mini
senderVersatile NiCd battery charger
-
or as e !very e ep oneyour order on 081-205 9558using
VISA/Access Card
art TECHNOMATICAll prices ex VAT.Prices are subject tochange
without notice.
Orders welcome fromgovernment depts &educational
establishments
Techno House 468 Church Lane. London NW9 8UF.Tel: 081-205 9558
Fax: 081-205 0190
MonFri: 9.15-5.30. Sat: 10.30-4.00
rchirriedes COMPUTERS
A3000 (no monitor)A3000 Acorn ColourA410/1 (no monitor)A410/1
Acorn ColourA410/1 Taxan 775'Acorn 420/1 systems420/1 (no
monitor)420/1 Acorn Colour
Acorn 440/1 systems440/1 Acorn Colour440/1 Taxan 775'Techno 410
1 systemsupgraded to 420 1 spec.Acorn Colour systemTaxan 770-
system
vouchers do nor apply to Taxan systems
Carriage £8/computer E12/s3 stem
£599£799
£1099£1299£1385
£1499£1699
£2299£2284
£1459£1699
SPECIAL FINANCIAL DEALComputers alone or complete systems can
bepurchased over 9 months. The deposit will bepayable with the
order followed by 9 monthlypayments. Please phone or write for full
detailsand a personal quotation. Subject to status. weshould be
able to despatch your order within 7days of receivina your
order
100o VOUCHER ON CASH &CREDIT CARD SALES
Cash and credit card purchasers of Archimedescomputers and
complete systems will receive avoucher to the value of 10clb of the
purchaseprice when purchased at the prices shownabove. Vouchers
will be valid for 90 days fromthe date of issue. Vouchers are not
available onTechno bundled packages.
Please add carriage(a) £8.00 (Courier, 2 days)(b) £3.50 (c)
£2.00 (d) £1.50Next day delivery atextra charge
What we offer in addition to efficientsales service and
professional backup!We not only offer professional advice when you
are purchasing your systembut we will also provide friendly
assistance afterwards. All our products carrya 12 month full
...,arranty for parts and labour.
TECHNO 410/1 SPECIALOffer extended due to popular
demand.Archimedes 410 1 upgraded to full440 1 specification with 4
MB RAM
and 50 MB Hard Disc (Acorn)plus
Taxan 770- Multisync Monitorand including Pipedream 3 and
Atelier as well asRISC OS Extras & SID Utilities
discs, a packet of discs, a printerlead and a mouse mat.
for only £1999 carr £12
TECHNO 410/40 UPGRADESA410/1 upgraded to 4 MB RAM and 40 MBHard
Drive complete with Mouse Mat. 1box of 3.5" discs, printer lead and
FirstWord Plus Release 2.Now with the Atelier art package &
RISC OSExtras & SID Utilities discsOur 40 MB Hard Drive is a
high spec. AutoPark.25ms. quality drive with a reliable
Toshibamechanism.
techno 410/40 with Acorn Colour Monitor£1699
techno 410/40 with Taxan 770- £1899Finance available on
chargeable bas s
technoTabletThe latest model of the Genius GT1212A PC tablet
adapted for use with Archimedescomputers offers a resolution of
1000 lines/in over a 12" x 12" working area and connectsthrough the
serial port of the computer.The Tablet is operated by moving a four
button puck controller over the special surfaceand a two button
stylus with switched tip is also available.The software to drive
the tablet is supplied as a module to operate within the RISC
OSdesktop environment. Once loaded. several commands are available
to control the tablet:
turn the tablet on or offselect relative or absolute coordinates
etc.change puck movement sensitivity
Three of the puck buttons act as standard mouse buttons and the
fourth allows specialoperations such as changing the size of the
tablet work area.
The tablet can virtually take over all the functions of a mouse
making the use of graphicspackages much simpler. The puck has a set
of cross -wires which allow simple andaccurate transfer of
technical drawings. The optional stylus will make tracings.
linedrawings etc much easier and more accurate.
The standard Archimedes mouse or a Tracker Ball can be left
connecfed and can evenbe used as alternatives for some
operations.The package includes the tablet. puck. software and
mains power supply.
GT1212A Tablet £259(a) PC mouse drivers andOptional Stylus
£35(d) and Art package £12(c)
TECHNO DTP PACKAGEArchimedes 410 1 Colour System
upgraded to full 420 1spec with 2 Mb RAM and 20 Mb
Hard disc featuring ourtechnoSCAN package and
RISC OS Extras & SID Utilitiesdiscs and the Atelier art
package
and either
Acorn DTP PackageFirst Word Plus Rel 2,
Logistixor
Impression and Pipedream 3and a free mouse mat
for only £1 777 carr £12Finance available on chargeable
basis.Special Educational Subsidy on
the Techno DTP package.
R140 UNIX SYSTEMLimited Period Offer
R140 Base Systemwith
Taxan 770- and PC Emulatoror
Viking IIplus
Ethernet Card andAdministrators Guide
for only
£3000and it also includes on -site
maintenance contract.
A3000 LEARNINGCURVE PACKAGE
with 1MB ACORN A3000Tutorial Video
GENESIS DatabasePC Emulator
FIRST WORD PLUSWordprocessor
the parents guide to the nationalcurriculum
A3000 LEARNING CURVE
£999Suitable monitor available
separately
TEL: 081-205 9558
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tt CONTENTS
July/August 1990Volume 16Number 180
In our next issue:
S -VHS RGB converter
36 -PAGE SUPPLEMENT OF CONSTRUCTION PROJECTSbetween pages 38 and
39
- i ill""High -current Hfetester LEADER rILight -dimming robot
11 Computers take over in the car
I
Mixer -amplifierIsolation amplifier COMPUTERS &
MICROPROCESSORS
_ -, I
Inter IC communications r, The 8031/8731 microcontroller ILF-HF
test probe by Dr David K yteAC motor control 37 PROJECT: Daylight
-resistant opto-isolator
Science & technology
Front cover52 DESIGN NOTES p. 49
Information about 'The 'Times
Atlas of the World' is among
more than one million authorita-
ELECTROPHONICSi PROJECT: MIDI master keyboard -Part2
..0.).,,L6,ti
tive records now stored on CD- by D. DoepferROM for use by
professional
librarians all over the world. GENERAL INTEREST \\A \ \ \ \ \The
British Library's National 16 PROJECT: Glow plug switch for 4
-stroke modelBibliographic Service has placed
comprehensive details of fiction
and non-fiction books published
rnin Britain since 1950 on the co-
pact disc system.
As the British National Bibliogra-
1S
enginesby A. PeperkampDecoupling power rails
4' 8 PROJECT: Door chime/alarm sirenby T. Giffard
i or -r 1-
phy (BNB) on CD-ROM is 56 In quest of a pangram Compact 10-A
power supplyexpected to be of interest to the by Lee C.F. Sallows
p. 19:-._:, c. academic and industrial
oraries of many countries, the
user interface can be switched
between English, Frenc- Ger-
man or Italian.
The system employs the same
INTERMEDUTE PROJECTS43 Versatile NiCd battery charger45
Reversing car alarm46 Electronic siren ... -
easy -to -use software as the 47 Simple square -wave
generatorws#
-,,,, . -
British Library General Cate- 47 Simple effective car theft
deterrent.. ,,.
1
a,.
loge of Printed Books to 1975,databases of the Biblitheque
Nationale of France, the
POWER SUPPLIES & BATTERY CHARGERS
14 PROJECT: Battery tester - an ELV design
44 '.,... ,--.,,.
...
Deutsche Bibliothek of West 19 PROJECT: Compact 10 A power
supplyGermany and the Library of by G. Boddington 100 MHz
TTL-compatibleCongress, USA. oscillator - p. 18!ri the background
of the photo-
graph is the beautiful and his-RADIO & TELEVISION
:oric Reading Room at the
British Library in London, which
s the site for research by peoplefrom all over the world.
18 PROJECT: 100by J. Bareforct
24 INMARSAT's Standardby B. Higgins
MHz TTL-compatible
C
oscillator
33 PROJECT: Mini FM transmitter - !..P' PvThe British Library by
J. BarefordBibliographic Services
2 Sheraton Street39 PROJECT: Sound demodulator for satellite
TV
receiversLONDON W1V 4BH by R.G. Krijgsman '.t 1-i-1Telephone 081
323 7255 --Facsimile:081 323 7039 49 SCIENCE & TECHNOLOGY
-..f.--rif
4
MISCELLANEOUS INFORMATION____Iila 4aili
---,.z.-4-,---- i,, : 41 41...
. -Electronics scene 12; New books 32; Events 61:Letters 62;
Switchboard 62; Readers services 63: Terms 64:Buyers guide 74:
Index of advertisers 74
The 8031 8731 microcontrollerp. 36
ELEKTOR ELECTRONICS KU /at; GUST 1990
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4Please mention ELEKTOR ELECTRONICS when contacting
advertisers
CLASS A AUDIO POWER AMPLIFIERS.3 COMPLETE SUPERMOS KITS NOW
AVAILABLE (complete down to the very last nut & bolt)
Move up to a better class of HiFi. build your ownultra high
fidelity audio power amplifier with ourFULL kits. Based on tried
and tested Supermostechnology. we now offer a choice of 3 FULL
kitsranging from 90Wichannel pure class A stereoamp to an earth
shattering 500W ch Supermos2based system.
The Supermosli2 modules are now recognisedworldwide for their
unequalled technicalexcellence combined with the very
bestaudiophile quality components. Our completekits cost around 1 8
that of commercial esotericand very overpriced HIFI's such as
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substantially better performance. Thuswe now bring esoteric classA
amplification withinthe budaet of the average HiFi enthusiast.
Our new kits are simple to assembledue to the use of a ready
built and testedmodular approach eliminating thevariable
performance otherwiseassociated with homemade kit HiFi's.
What Do You Get- ?Compared to commercial amplifiers costing
manytimes more. there are few amplifiers that canoffer ANY of these
features at any price! TheSAGE SUPERMOS2 kits offer ALL
thesefeatures. and much much more.
Pure Class A operation into any speaker load withoutspurious
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Kit I Complete stereo 90W chincludes the following-
2xSupermoslmodules. total 40.000uF capacitors.2x35amp bridges
rectifiers. 2xDC protectionmodules. 1xtransformer softstart
unit.1x400VA toroid. 1xblack textured finishedcase 280xx190x90mm.
1x hardware packcontaining all input output plugs sockets.
clips. fuses, cable ties. assemblyinstructions etc. Total
component price £328full kit price just £299 p&p £6 (UK).
Kit 2 As above but monoblockconstruction yielding over 100W ch.
twoKIT 2's are required for stereo price of totalcomponents is
£201. FULL kit price £180p&p £6 each.
Kit 3 Top of the range. Supermos2based stereo kit complete as
kit 1 exceptwithout toroids and includes a total88.000uF
capacitance. Power output user
defined by transformer rating power outputsfrom 100W to 500W.
total component costis £483 kit price just £430 p&p £9
In addition. all kits come with a £30discount voucher off the
purchase of aDigitrap2 compact disc digital noisefilter, normal
price £62.
To order direct please send a cheque payable to SAGE AUDIO and
send to the address below.To obtain more information on these and
all our products please send a large SAE together with
£2 coins (Overseas pIease send 6 International reply coupons) to
SAGE AUDIO,
Construction House, Bingley, W' Yorks BD16 4JH England.
EPROM ERASERWIPEOUT!
Just DCP oriis P&P & VATPerfect condition erasers hold
up to 40 EPROMS.Ideal for home use and in development labs.
We must sell 100 of these to makeway for a new model.
Send Cheque with order or telephone with credit carddetails. 1st
come 1st served.
We also have available: -A wide range of components. Cross
Assemblers.EPROM Programmers and Microprocessor basedcontrol
cards.
Call us today for more details and your freecopy of our
catalogue on v,di(035 388) 325 or 455 LAIVIA
Ai&J. P. istribution.
The Old School. Prickwillow. Ely. Cambs. CB7 4UN
ft Happy Memories4116 150ns only pulls £1.00 2716 450ns 5 Volt
£3.204164 100ns 64K x 1 £1.25 2532 450ns Only pulls £3.5041256
100ns 256K x 1 £2.25 2732 450ns £2.1541464 100ns 64K x 4 £2.75 2764
250ns £2.1544256 100ns 256K x 4 £7.50 27128 250ns £2.2541000 100ns
1024K x 1 £6.95 27256 250ns £2.456116 150ns Low power £1.45
27C256250ns £2.456264 100ns Low power £2.45 27512 250ns £4.7562256
100ns Low power £5.95 27C512250ns £4.75SIMMS 100ns 1 Meg x 9 £75.00
and 8Ons £79.00
Please call for prices of other chips. Same chips but different
speecs.quantity discounts etc. Second (pulled) chips available for
many of theabove devices at substantially lower cost. Call for
availability and price
of these and other items.
Low profile IC sockets: Pins 8 14 16 18 20 24 28 40Pence 5 9 10
11 12 15 17 24
We always have a large quantity of surplus computer equipmentfor
sale; printers. disk -drives, add-on boards, monitors etc:Please
ask for our surplus equipment list or call with your
requirements as new items are added so frequentlythe list is
never up to date !
'ease add 50p post & packing to orders under £15. VAT to be
addedtotal. Access orders by 'phone or mail welcome. PLC.
government &Educational orders welcome for minimum invoice
value of £15 net.
HAPPY MEMORIES (EL), FREEPOST,Kington, Herefordshire. HR5
3BR.Tel: (054 422) 618 Sales, 628 fax MEM
VISA(no stamp needed unless first-class required) 111.
LLEKTOR ELECTRONICS JULY AUGLST 1990
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Produced and published by ELEKTORELECTRONICS (Publishing)
COMPUTERS TAKE OVER IN THE CAREditor/publisher: Len
SeymourTechnical Editor: J. SuitingEditorial Offices:Down
HouseBroomhill RoadLONDON SW18 4J0EnglandTelephone: 081-877 1688
(National)or -44 81877 1688 (International)Telex: 917003 (LPC
0)Fax: 051-874 9153 (National)or -44 81874 9153
(International)Advertising: PRB Limited3 Wolseley TerraceCHELTENHAM
GL50 1THTelephone: (0242) 510760Fax: (0242) 226626European
Offices:Postbus 756190 AB BEEKThe NetherlandsTelephone: +31 4490
89444Telex: 56617 (elekt nI)Fax: +31 4490 70161Managing Director:
M.M.J. Landman
Overseas editions:FEDERAL GERMANYElektor Verlag GmoHaisterfeld
&ratite 255100 AachenEditor: E.J.A. KrempelsauerFRANCEElektor
sariRoute Nationale: Le SeauB.P. 53; 59270 BailleulEditors: D.R.S.
MeyerG.C.P. RaedersdorfGREECEElektor EPEKariskaki 1416673 Voula -
AthenaEditor: E. XanthoulisINDIAElektor Electronics PVT LtdChhotani
Building52C, Proctor Road. Grant Road (E)Bombay 400 007Editor:
Surendra lyerNETHERLANDSElektuur ByPeter Treckpoelstraat 2-46191 VK
BeekEditor: P.E.L. KersemakersPAKISTANElectro-shop35 Naseem
PlazaLasbella ChavricKarachi 5Editor: Zain AhmedPORTUGALFerreira
& Sento Lda.R.D. Esterani, 32-V1000 LisboaEditor: Jeremias
SequeiraSWEDENElectronic Press ABBox 550514105 HuddingeEditor: Bill
Cedrum
Distribution:SEYMOUR1270 London RoadLONDON SW16 4DH
Printed in the Netherlands by NOB.Zoetenvoude
Copyright i; 1990 Elektuur BV
ABC
Motorists may not normally be thought ofas computer operators.
yet the inescapablefact is that the electronics and micorchipsof
the computer age are now becoming in-volved in virtually every
aspect of moderncars, from engine control to braking.
There are even suspension systems inwhich a computer takes the
place ofsprings, while electronics are increasinglypart of in -car
entertainment and mobilecommunication systems.
In Britain, road and traffic experts arealready well on the way
to developing apractical computer -based system that willserve as
both an aid to car navigation anda means of avoiding traffic
congestion.
The latest Jaguar XJ6, for instance, hasno fewer than seven
computers that lookafter the engine, suspension and brakes,cruise
control and the vehicle's sophisti-cated air-conditioning
system.
Many of the latest car engines haveelectronic management systems
that bringhigher levels of efficiency and economy.Typical of recent
advances is the ModularEngine Nlanagemat System-MEMS-de-signed and
developed by the RoverGroup. This controls functions such asfuel
injection, emissions and spark timingfrom a single microchip
unit.
Totally interlinked systems
NlEMS has its own 8 kbyte memory andalso helps in servicing the
engine, as themicroprocessor can signal any developingfaults.
Paul Ryder. head of engine manage-ment at Lucas Components, one
ofBritain's leading electronic car systemmakers, recently predicted
cars in die nearfuture with interlinked electronic systemsin which
chassis, engine and brake con-trollers would share the information
fromtheir various sensors to manage the car asa whole.
A new £10 million research centre setup by Ford in Britain
houses Europe'smost modern test equipment for automa-tive
electronic systems. including themost advanced spark plug
laboratory andthe largest anechoic chamber for researchinto in -car
audio entertainment systems.
Sensors and electronic engine manage-ment systems such as Ford's
EEC IV aretested there, while the anechoic facil-ity-a chamber
designed to be free fromall echoes and sound reflections-is usedto
perfect audio equipment.
The centre is also working v. ith inter-national broadcasting
authorities on radio
data systems that avoid the need to retunemanually to the
strongest signal in differ-ent areas. These systems also
allowdrivers to be given traffic information au-tomatically for
their location.
Used by the champion
Sports car manufacturer Lotus is perhapsthe best-known developer
of active, orcomputerized. suspension systems. NigelMansell drove a
Lotus 92 racing car fittedwith this type of suspension in
GrandsPrix as long ago as 1983.
Lotus systems use microprocessor -con-trolled hydraulic rams
powered by the en-gine to control the wheels' path overbumps. as
well as chassis braking, corner-ing and pitching of the car
body.
So far no mass production car has yetbeen made with this type of
sophisticatedcomputerized suspension. However.Rolls-Royce,
traditionally among themost conservative of designers,
recentlyintroduced a microchip -controlled auto-matic ride control
system said to be un-equalled.
In this, the stiffness of the suspensionadapts in only 1/100th
of a second tochanges in road conditions and selects theappropriate
'comfort', 'normal' or 'hard'setting automatically. To do so, it
uses amicroprocessor and sensors that continu-ously monitor
acceleration, road surfacecondition, braking and steering
changes.
A new era of computer -aided vehiclenavigation seems to be just
around thecorner. Drivers in London, for instance,will by 1993 have
access to a an advancedguidance system that promises to cutdown
both journey times and driver fa-tigue.
The GEC Autoguide system has beenchosen for a government
-sponsored pilotscheme that will be operational in centralareas of
the city next year. It will providethe driver with up -to -the
minute direc-tions for the best route to a chosen desti-nation by a
dashboard -mounted displayand audible instructions.
The heart of this system is a centralcomputer that notes current
journey timeson each route. continuously updates cal-culation of
preferred routes, and broad-casts instructions to drivers from
roadsidebeacons using an infra -red beam.
Later, it may even be able to adviseabout the availability of
parking space ina chosen area. Urban motoring will justnot be the
same again.
ELEKTOR ELECTRONICS JULY/AUGUST 1990
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RADIOCOMMUNICATIONSEXECUTIVE AGENCY
The Radio Communications Division ofthe Department of Trade and
Industry hasbecome the Radiocommunications Agencyas one of the
government's 'Next Steps'Executive Agencies.
The creation of Next Step ExecutiveAgencies within Government is
part of theNext Steps Initiative launched by theprime minister in
February 1988. They aredesigned to bring about lasting
improve-ments in the quality and efficiency of gov-ernment services
to the benefit of cus-tomers and texpayers.
There will not be a lot of immediatedifference between the old
Radiocommu-nications Division and the new Radiocom-munications
Agency, but over time thechange will be substantial. According
tothe chief executive of the new agency, "wewill be working hard to
face the chal-lenges of the 1990s and to build on theprogress
achieved by the Radiocommuni-cations Division in recent years. In
partic-ular, Agency status will give us an addi-tional incentive to
provide an improved,effective, quality service to radio
usersthroughout the country."
TEST SET FOR DIGITALTELEPHONE NETWORKS
A low-cost, easy -to -use error -performancetester for digital
telephone networks oper-ating between 2 and 140 Mbit/s has
beenintroduced by Uplec Industries.
Designed to comply with the specifica-tion for British Telecom's
414A tester, theType 4301 Test Set will be useful to allerrs using
ccirr telecom standards andother providers of
telecommunicationsnetworks. It has been officially approvedby
British Telecom.
Operating at 2.048, 8.448, 34.368 and139.264 Mbit/s over 75-0
lines and2.048 Mbit/s over 120-f/ balanced lines,the 4301 generates
a pseudo -random bit
sequence to ccrrr Standard 0.151 and a16 -bit programmable word
pattern to mon-itor the error performance of digital tele-com
networks.
Intended for field operation, the 4301weighs under 10 kg and can
operate from200-250 V 50-60 Hz supplies. An internalNiCd battery
maintains settings and datafor up to 30 days.
Uplec Industries Ltd, Oakhurst Hall,Oakhurst Road, OSWESTRY SY10
7BZ.Telephone (0691) 650422; Fax (0691)658553.
ABERDEEN ENGINEERINGSTUDENTS WIN PLACE ON
NASA SHUTTLEEngineering students from Robert Gor-don's Institute
of Technology in Aberdeenwere given a boost recently when
theylearned that their project to test thestrength of gravitational
fields at altitudewould be sent into orbit on board a NASAspace
shuttle next year.
The group had competed against twoother teams from Nottingham
and HatfieldPolytechnics in the national final of theSpace Shuttle
Competition organized bythe Institution of Electrical Engineers
andBritish Sugar.
The nationwide competition waslaunched in 1988 to give
engineering stu-dents the opportunity to design and build asmall
self-contained payload to be carriedon NASA'S Space Shuttle 4060.
Space onthe shuttle (a 'Getaway Special') wasbought from NASA by
British Sugar anddonated to the Institution.
The winning team now have one yearto build their project ready
for launchlate next year. Financial and practicalsupport will be
given by British Sugarand local industry.
BBC's TIME SIGNALEarlier this year, the BBC assumed
re-sponsibility for the generation of the 'sixpips' time signal.
The pips had since 5February 1924 been generated at 15 -minute
intervals by the Royal Green-wich Observatory.
The new Time and Frequency systemhas been designed to provide
accuratetime and frequency signals to users inthe BBC Network Radio
and other BBCareas as required.
The Time Standard uses three off -airradio receivers in a triple
redundancyformat. Two of these derive time/dateinformation from
Global PositioningSystem-cPs-satellites, while the thirdis a low
-frequency receiver capable ofreceiving MSF at Rugby or DCF at
Mann-flingen in Germany. Time and date in-formation from all three
receivers is pro-cessed via a specially designed 'TimeVoting
Switch' which ensures that therest of the system receives
accuratetime/date information, even if off -air re-ception is lost
for a period.
The Frequency Standard has two ru-bidium atomic oscillators in
dual redun-dancy configuration. Each oscillator ismounted in a GPS
receiver and any driftis automatically compensated by off -airGPS
signals, thus avoiding the need ofregular calibration of these
units. The re-sulting accuracy and stability of the fre-quency
standard is half -way between aconventional rubidium system and
acaesium system, and as such this systemcan act as the primary
timing level in adigital transmission system.
BBC Engineering Information,Broadcasting House, LONDON W1A1AA.
Telephone 081 927 5432.
01-5.5 GHZ PLASTIC -PACKAGEDSILICON MMIC
9
Avantek has now available a plastic -packaged version of its
highest -fre-quency monAmPTm silicon monolithic lcamplifier.
Designated MSA-0986, themmrc amplifier provides 7.2 dB gainwith
±0.5 dB gain flatness from 01 GHzto 3.0 GHz, and a 3 dB bandwidth
oftypically 0.1 GHz to 5.5 GHz. At 2 GHzthe unit provides +10.5 dBm
outputpower, a noise figure of 6.2 dB, typi-cally 1.6:1 input and
1.8:1 output vswit(0.1-3.0 GHz) and is unconditionallystable.
Avantek Inc., 481 Cottonwood Drive,IvilLPTI'AS, Ca 95035-7492,
or, in UK:Wave Devices, Laser House, 132-140Goswell Road, LONDON
EC1V 7LE.
ELEKTOR ELECTRONICSK1N/AUGUST 1990
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UNIVERSAL COMPUTER/PRINTERBUFFER
Micro Control Systems has developed acomputer memory unit that
provides aprinter buffer with two inputs and two out-puts. The
advantages of the `X Buffer' in-clude the ability to connect any
computerwith a serial or parallel output to anyprinter with a
serial or parallel input-equipment that would otherwise be
in-compatible. The buffer memory starts at64 kbytes and can be
expanded with plug-in modules up to 4096 kbytes, big enoughto store
a very long document or even awhole book (over half a million
words).
Micro Control Systems Ltd, ElectronHouse, Bridge Street,
SANDIACRENGIO 5BA.
DUXFORD RADIO SOCIETYThe Duxford Radio Society was formed
in1986. It saw its beginnings during the pre-vious two years when
former members ofthe Special Forces Signal Section operateda radio
station from Duxford to celebratethe 40th anniversaries of D Day
and VEDay in 1984 and 1985 respectively.
LONDON
The association between the societyand the Imperial War Museum
was put ona firm footing when in September 1986the society's call
sign GB2IWM was regis-tered at the Home Ofice. Since then, regu-lar
exhibitions of communications equip-ment relating to particular
themes havebeen held at Duxford on special eventdays. The radios
and associated items ondisplay are from both the Imperial
WarMuseum's communications collection andmembers of the Radio
Society.
The society is not an Amateur RadioClub, but aims to combine
amateur radiowith interest in radio history and to offer
OA] r;',11
some expertise in the documentation,restoration and operation of
historic mili-tary and clandestine radio gear.
Duxford Radio Society, Duxford Air-field, CAMBRIDGE CB2 4QR.
Tele-phone (0223) 833963.
NEW DEVELOPMENTS INTRANSFORMER TECHNOLOGY
At present, the majority of condition mon-itoring techniques for
transformers rely onthe detection of a fault. Provided the
faultevolves relatively slowly, the consequen-tial effects can be
minimized.
Progressing a stage further, ERA Tech-nology is developing
Frequency DomainMeasuring-Fiat-techniques capable ofdetecting a
weakness, rather than a fault,within the transformer. The types of
weak-ness that the techniques will uncover, forinstance, winding
displacement or slack-ness, often remain undetected and can leadto
catastrophic failure and unplanned out-age if they ate not treated.
Winding slack-ness in particular can be removed and fur-ther damage
prevented.
The techniques being developed workby identifying and tracking
resonantmodes exhibited by any electrical wind-ing. It is generally
recognized that the res-onant behaviour of a winding is
stronglyinfluenced by changes in the relative posi-tion of winding
conductors or, indeed, therelative position of the windings. The
pre-sent development makes use of a swept si-nusoidal source to
excite winding reso-nances.
Experimental work at ERA has alreadyproved that FDM techniques
can identifycertain specific forms of winding distor-tion. These
include extreme winding col-lapse, axial displacement between
concen-tric windings and winding slackness.
Two forms of Film test instrumentationare also being developed b
y ERA. Thefirst of these, static FDM testing, involvesan assessment
of the windings in their`rest' or static positions. Developmentwork
to date allows a number of windingfaults and displacement disorders
to be de-termined from typical test data.
Work is also being carried out on dy-namic FDM testing-that is,
the process oftracking dynamically the movement ofconductors. ERA's
objective is to developinstrumentation that will provide a
mea-surement of winding slackness. A tech-nique capable of
dynamically tracking
winding vibration is currently being evalu-ated and ERA hopes
ultimately to apply itto on-line monitoring.
ERA Technology Ltd, Cleeve Road,LEATHERHEAD KT22 7SA.
Telephone(0372) 374151.
UL RECOGNITION FOR SILICONIXPOWER TRANSISTOR MODULES
Siliconix's Type SPMB50A500 and TypeSPMF50A500, a range of 500
V, 50 A ISO -POWER transistor modules, have UL statusas recognized
components under SectionQQQX2-Component Power
SwitchingSemiconductors.
UL recognition means that the modu-lates have been 100% tested
to ensure thatthey conform to UL safety standards for2500 V
insulation and flammability intough industrial applications.
The modules allow the construction ofmotor controls and power
supplies withoutthe need to parallel discrete transistors.They will
operate directly from 240 Vpower lines, thus reducing parts
count,size and weight of power conversionequipment.
Siliconix Ltd, Weir House, OverbridgeSquare, Hambridge Lane,
NEWBURYRG14 5UX. Telephone (0635) 30905.
ADD-ON MODULE FORSATELLITE TV RECEPTION
An add-on unit is claimed to save TVviewers about £200 on the
cost of satelliteTV. The unit, about 100x75x25 mm, con-verts
existing TV receivers and videorecorders so that they can be used
to watchand record the new satellite channels aswell as the
terrestrial broadcasts. Viewersstill need a dish, but will no
longer have tobuy or rent a separate set -top converter.
The unit, developed by Zeta Services,allows viewers to do what
most convertersdo not: watch one satellite channel whilerecording
another-most current set -topconverters can pick up only one
channel ata time.
The Zeta module uses the spare tuningcapacity built into most
modern TV setsand VCRS. Many of these can be set to tuneinto up to
99 channels. The unit leavesplenty of space for the current and
plannedterrestrial channels, but mere the remainderof the tuning
capacity for existing and fu-ture satellite channels.Zeta Services
Ltd, Harden Park, ALDER -LEY EDGE SK9 7QN. Telephone (0625)583850;
Fax (0625) 585282.
ELEKTOR ELECTRONICS JULY. AUGUST 1990
-
BATTERY TESTER
This compact tester,designed and marketedas a kit by ELV, has
three
LEDs that indicate thecondition of
alkali -manganese,carbon -zinc, and
alkali -zinc primarybatteries of the mignon,
mono, baby orpower -block type.
The growing mass of battery -poweredequipment brings with it the
need of quickbattery condition testing. The battery tes-ter
described here helps you to preventgetting stuck, at crucial
moments, with aflat battery or battery pack in, for instance,a
cassette recorder, a torch, a remote con-trol unit or a personal
radio.
The tester is simple to use: the primarybattery to be tested is
connected by twotest clips and flexible wires. Three LEDswith
different colours immediately indi-cate whether the battery is as
good as new('full'; green LED), usable (yellow LED),or exhausted
('empty'; red LED).
The tester is automatically actuatedwhen a battery is connected
to the testleads. This does not work, however, whenthe battery is
completely exhausted.When this is suspected, the TEST button
lAger, Bab, Yana V b.%OM O aswR 4GF ZA
all Battery Tester
must be pressed to prove to the user thatthe battery is really
exhausted, or that theinternal 9-V battery of the tester itself
isflat. When the red LED lights in this con-dition, the battery
under test is completelyempty.
Circuit descriptionThe circuit diagram of the battery tester
isgiven in Fig. 1. The circuit is powered bya 9-\' (PP3) battery.
of which the _termi-nal is connected to PCB terminal ST3, andthe
-terminal to PCB terminal ST4. Thetest circuit is powered only when
transis-tor Ti conducts. Normally, TI is held offby R25 so that the
circuit does not receivea supply voltage.
When the TEST button, Tat, is pressed,Ti receives base current
via R24 and con-sequently starts to conduct. The test cir-cuit then
receives its supply voltage. Thecircuit is actuated in a similar
mannerwhen a voltage greater than about 0.65 Vexists at the input
terminals, ST1 and 5T2.In that case, resistor R22 feeds a base
cur-rent into transistor T2. The resultant basecurrent of Ti causes
the tester to beswitched on automatically.
The load resistance of the batteryunder test is determined by a
four -posi-tion slide switch, Si, and one of fourpotential
dividers:
'Mignon (IEC R6) batteries:R1-R7'Baby' (IEC R14)
batteries:R2-Rs'Mono' (IEC R20) batteries:Rs-R9
kT
mon M449-11 S14
Fig. 1. Circuit diagram of the battery tester. The batery type
is selected with a four -position slide switch. S1.
LLEKTOR ELECTRONICS JULY/AUGUST 1990
-
BATTERY TESTER
O 00 00O 00 00
of 10 .01 ,._ lo o.04 = 10
el -100000
0 0 0 0[5.=10
a. loo{===107W -0- -0 0
-41 -
ziS111 a
-411111-
--041!1-
NI. -emir_
-4118*. _
11111-
-
'94/ power -pack' (IEC 6F22) batteries:Rs-Ro-R it
The voltage at the junction of the potentialdivider (R1 -R11)
selected with St is fed tothe -inputs (pins 2 and 6) of
comparators10A and 10 B. The +inputs of these corn-parators are
held at a reference level cre-ated by zener diode Di and
potentialdivider 1213 -Rio. Resistor R12 limits thecurrent through
this stabilizer, whoseinput voltage is decoupled and bufferedby
electrolytic capacitor Ct. Feedback re-sistors RI7 and Ris provide
a certain hys-teresis to ensure flicker -free operation ofthe
LEDs.
When the battery voltage exceeds theminimum value of 1 V, both
comparatoroutputs, pins 1 and 7 of IC IA and 10s, areat a high
potential, so that the red LED, D4,lights. When the batten' voltage
is be-tween 1.0 V and 1.3 V, the output of 'CIAremains high, but
that of IC113 goes low.Consequently, the red LED goes out, andthe
yellow LED, D3, lights. When the bat-tery voltage exceeds about 1.3
V, [CIA tog-gles, so that only the green LED, D2, lightsto indicate
that the battery is full.
The above comparator switching thre-sholds apply to the three
types of 1.5-V
COMPONENTS LIST
content of kit supplied by ELV France
Resistors:2 1115 R3;R92 3123 R2:R82 5126 Rt;R72 150 R6;R111
15052 R5
1 68011 R12
4 1k0 1315;1319:F120:R21
1 3k3 R163 10k R22;R24;R251 15k R14
1 100k R23
2 WO R17;R181 5k preset H R13
Capacitors:2 10oF 25V radial C1 ;C2
Semiconductors:1 11.1358 let1 ZPD3V3 Di1 BC548 T21 8C558 T11 LED
3mm red D41 LED 3mm yellow D31 LED 3mm are en 02
Miscellaneous:1 PCB -mount push button Tat1 4 -way 1 -pole slide
switch Si2 test lead with crocodile clip1 battery clip6 solder
pin-15rnm silver-plated wire1 printed circuit board1 enclosure
A complete kit of parts for the batterytester is available from
the designers'exclusive worldwide distributors (re-grettably not in
the USA and Canada):
ELV FranceB.P. 40F-57480 Sierck-les-BainsFRANCETelephone: +33
82837213Fax: +33 82838180
battery that can be tested. For 9-V PP3batteries, they lie at
about 6.0 V and 7.8 V.
Preset R13 is adjusted to give a refer-ence voltage of 0.65 V at
pin 3 of ICI. Thisadjustment is made with a full batteryconnected
to ST1-ST2, i.e., the input volt-age must be 1.4 V or greater.
ConstructionThe construction of this small circuit isrelatively
simple. Start by fitting thesingle wire link on the board, followed
bythe resistors and the zener diode. This parthas a coloured ring
to mark the cathode.
Next, fit the three LEDs so that theirtops are about 15 mm above
the boardsurface. The cathode of a LED is usuallymarked by the flat
side of the plastic body.When the device is held against the
light,the cathode is identified as the larger met-al surface. The
LEDs in this circuit are notnormally damaged when fitted the
wrongway around.
The last components to be fitted on theboard are the capacitors,
the transistors,the integrated circuit, the slide switch andthe
TEST button. Finally, connect the redwire of the battery clip to
PCB terminalST3, and the black wire to PCB terminalST4.
Two flexible test leads with crocodileclips are supplied with
the kit. The redlead (for the positive battery terminal)
isconnected to PCB terminal ST1, and theblack lead (for the
negative battery termi-nal) to PCB terminal ST2. The test leadspass
through 2 -mm dia. holes drilled inthe short side of the top half
of the enclo-sure. Make a knot in each wire, at about20 mm from the
free end, to provide somestrain relief.
Fit the completed printed -circuit boardinto the top half of the
enclosure, aligningits central hole over the moulded boss andmaking
sure that the LEDs go into therespective holes. Then connect the
9-Vbattery and fit the other half of the enclo-sure with the self
-tapping screw supplied.
ELEKTOR ELECTRONICS JULY/AL:GUST 1990
-
16
GLOW PLUG SWITCH FOR4 -STROKE MODEL ENGINES
A. Peperkamp
A notorious problem with four-stroke model engines is
theirtendency to stutter or even stall at low speeds with all the
obviousrisks of carefully wrought model aeroplanes fluttering
helplessly
about before crashing to the ground. This circuit gives ease of
mindto aeroplane modellers by automatically switching on the glow
-plugwhen required at low engine speeds to keep the combustion
going.
Among the conditions for a reliably run-ning model engine are a
correctly ad-justed carburettor, the use of the rightfuel, and a
suitably rated glow plug. Thelatter is fitted to ensure a
sufficiently hightemperature in the combustion chanber ofthe engine
to enable this to be started. Aglow plug is normally powered by a
start-ing battery, which may be disconnectedonce the engine is
running.
Most engines in model aeroplanes are2 -stroke types with glow
ignition. Recent-ly, however, 4 -stroke types have becomeavailable
with two main advantages: first,they produce less noise, and,
second, theirsound is more like that of a real
aeroplane_Unfortunately, 4 -stroke engines also havedisadvantages
with respect to 2 -stroketypes: their fuel/performance ratio
isworse, their construction is more com-plex, they weigh more, and,
importantly,their combustion is optimum at relativelyhigh speeds
only. When a 4 -stroke engineruns at low speed for some time, its
oper-ating temperature drops to a level wherecombustion strokes
fail, or the enginestalls altogether. Clearly, the additionalheat
of the glow -plug may help to preventthis happening. The present
circuit con-nects the glow plug to a battery on boardthe plane.
This connection is made auto-matically when the engine speed
dropsbelow a certain value.
Not the mechanical way...A simple form of mechanical control is
alever switch coupled to the acceleratorservo. In practical terms,
this can take theform of a cam or notch in the servo discoperating
a switch when a certain position(corresponding to a given engine
speed) isreached. The switch, in turn, connects orbreaks the supply
voltage to the glowplug. The main problem of this approachis
finding the right switching point by ex-perimenting with a running
engine. Also,taking into account that space is always ata premium
in a model, a mechanical con-struction with a lever and a switch,
how-ever small, can become very complexindeed and take a lot of
time to install andadjust.
...but with electronics!The first 'electronics' idea that comes
tomind is, of course, replacing the leverswitch by a relay or a
power transistor.The choice in favour of the latter will beobvious
in view of reliability in a fairlyhostile environment (vibration
and shockcaused by the model). The next step is toeliminate the
mechanical coupling to theaccelerator servo disc. Instead, the
rele-vant pulses received from the remote con-trol transmitter are
accepted andprocessed in parallel by a special circuit
0
50
12
-7 a
ICI.at
C3
74
ICI
X11 TICUS
IN1143i
TO
1141143
ICI=4Ma B$170 o
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3B5170
0
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20:03 - I.
Fig. 1. Circuit diagram of the glow plug control.
i.e., the glow plug switch is controlled bythe accelerator servo
pulses supplied bythe receiver on board the model. When thepulse
-width of the accelerator control sig-nal reaches a certain
(predefined) levelcorresponding to a relatively low enginespeed,
the glow -plug is automaticallypowered, and switched off when the
en-gine is revved up again.
Powering the glow plugGlow plugs fitted in model engines
gener-ally operate from a 1.5-V supply. Depend-ing on the type, the
current consumptionis usually between 2 A and 4 A. Providedthe
switch is virtually loss -free, a NiCd(nickel -cadmium) battery
with a capacityof 1.2 Ah or 1.8 Ah mar be used as apower source.
Since the glow plug isswitched on at low engine speeds only(e.g.,
while the model idles on the ground,or while descending or
landing), this sortof battery capacity is sufficient for a num-ber
of flights.
The author has fitted one of his modelswith a 9 -way sub -D plug
for outboardcurrent supply and charging of the re-ceiver battery as
well as the glow plugbattery. A switch is added to enable theglow
plug to be powered by an external(outboard) battery or power supply
dur-ing starting on the ground. At the sametime, this external
power source chargesthe on -board battery. When the switch isset to
the 'fly' position, the glow -plug bat-tery is connected to the
control board.
Circuit descriptionThe circuit diagram of the glow plugswitch is
given in Fig. 1. The power FET,T4, used to switch the current to
the plug,has a typical on -resistance of 0.04 n. Thisextremely low
value is only achieved,however, at a sufficiently high gate
volt-age. Since the battery voltage is usually4.8 V in models,
voltage doubling is usedto ensure that T4 can be driven into
satu-ration.
The voltage doubler consists of T2, Di,D2, C4 and R4. The
circuit supplies an out-
ELEKTOR ELECTRONICS JULY 'AUGUST 1990
-
GLOW PLUG SWITCH FOR 4 -STROKE MODEL ENGINES
Fig. 2. Printed -circuit board for the glowplug switch.
COMPONENTS LIST
Resistors:1 10k1 68k1 33001 82002 100k1 50k preset H
Capacitors:1 101iF 25V1 47nF1 2112 25V radial2 471.1F 25V
radial
RI.
R2
R3R4
R5:R6Pi
C1
C2C3C4:C5
Semiconductors:2 1N4148 01:021 LED D3
1 39V 0.4W zener diode D43 BS170 ;T2:T3
1 11211 T41 4538 ICI
put voltage of about 9 V across C5. Thiscapacitor is discharged
by R5 after the re-ceiver is switched off to ensure that T4 isoff
no longer than 3 seconds afterwards.The value of Rs is a compromise
betweenrapid turning off of 14 after the receiver isswitched off,
and a small load for the volt-age doubler. The PWM (pulse
-widthmodulated) signal taken from the acceler-ator servo terminals
provides the clock forthe voltage doubler, obviating a
separateoscillator.
The drive signal for the power FETgenerated by two monostable
multivibra-tors, ICI: and ICis. The former suppliesan output pulse
at the leading edge of thePWM input signal. The pulse width of
thisoutput signal (available at pin 6) may beset to a value between
0.5 ms and 3.0 msby adjusting preset Pi.
Monostable !CIF; is wired to trigger atthe trailing edge of the
pulse supplied byICI A, i.e., when the receiver output signalis at
'0'. The control signal for T4 is takenfrom the Q output of ICis
and applied tothe gate via a small -signal FET, T3.
0
CP.hartext witherria
battery
2charge on -board
.,'" battery
CP batterycharge receirer
servo controlof carburettor
S2 a
0er
battery
charge flyre- -en
0
S ow plugcwitcr. control
engine ground connection
R-CRX
Jon 900028-12
Fig. 3. Interconnections in a model aeroplane.
LED D3 forms the glow plug on/offindicator. Where appropriate,
it may bereplaced by an actuator such as a low -power piezo buzzer.
The engine speed atwhich the glow plug is switched on maybe
adjusted with PI.
Construction and wiringThe printed -circuit board for this
circuit issmall (Fig. 2) in view of the restrictedspace in the
model. Jumpers A and B allowthe control to be geared to the
polarity ofthe servo control signal supplied by the
remote -control receiver.The wiring between the control
circuit,
the two batteries, the glow plug, the'charge/fly' switch and the
9 -way sub -Dconnector is connected as shown in Fig. 3.Be sure to
use heavy-duty wire for theconnections that carry the glow plug
cur-rent.
The current consumption of the circuitis negligible relative to
that of the glowplug. In the off state, about 1 mA is drawn,in the
on state, about 12 mA, mainly onaccount of the LED. - -
ELEKTOR ELECTRONICS JULY/AUGUST 1990
-
18
100 MHz TEL- OMPATIBLECRYSTAL OSCILLATOR
J. Bareford
2
Al
XI 152 C2
ItoOMHz 22P
T2
L2
ICI
C4
6-133p R3
8F982 Dll
T1N4148;:r
caw = ICI = 74F00 893176 .
*see text5V
The use these days of clock frequencies ofup to 100 MHz is not
uncommon in digitalsignal processing (DSP) equipment,
RFsynthesizers, video storage circuits andlogic analysers. The
circuit described hereis based on a quartz crystal, and suppliesan
output signal of 100 MHz with suffi-cient drive capacity for TTL
circuits.
The circuit consists of three sections: aquartz -crystal
controlled oscillatoraround XI and Tt; an impedance conver-ter, T2,
and an output buffer, ICI.
Tuned circuit L1 -C2 is designed tomake the quartz crystal, Xi,
operate at itsfifth overtone (i.e., its fundamental, paral-lel
-resonant, frequency is 20 MHz). Posi-tive feedback in the
oscillator is providedby C5 between the emitter and the base
ofTi.
Since the oscillator must be loaded aslightly as possible to
prevent startingproblems and instability, the output sig-nal is
applied direct to a dual -gate MOS-FET, T2, of which gate 1 forms a
very highimpedance. The high transconductance ofthe N1OSFET enables
the oscillator signalto be taken from the drain at a relativelylow
impedance. Network R3 -Di raises thetop level of the 100 -MHz to
above the TTLthreshold for a logic 1 (approx. +2.42 V).
Four parallel -connected NAND gatesin a 74F00 or 74AS00 package
are used todigitize and boost the oscillator signal.The 5-Vpp logic
swing of the output signalenables it to be applied direct to
TTL-com-patible clock inputs.
ConstructionThe oscillator is best constructed on thesmall,
double -sided printed -circuit boardshown here. The component side
of this
board has a ground plane of unetchedcopper to assist in
decoupling the high -frequency signal.
Start the construction with windingthe two inductors. Li
consists of 10 turnsof 0.5 mm diameter enamelled copperwire
(e.c.w.), and has an internal diameterof 3 mm. L2 consists of 25
turns of 0.3 mme.c.w., and also has an internal diameterof 3 mm.
Use the shaft of a 3 -mm drill asa former to make these inductors,
whichare fitted just (
-
MPACT 10-A POWG. Boddington
SJPPLY
It has been some time since we published a 200+ Watt powersupply
like the one described here. Capable of supplying up to 10 A(and
more if so configured) at an output voltage range of 4 to 20 V,
this ultra -reliable PSU uses a minimum of components and
issimple to build.
If there is one instrument in the electronicsworkshop or
laboratory you must be ableto rely on at all times, it is the
powersupply. These days, a d.c. power supplywith excellent
regulation, low noise out-put and high output current can be
builtwith relatively few components. The pres-ent design is based
on the well-knownType L\t317 integrated regulator. Sincethe LN1317
is capable of supplying an out-put current of 'only' 1.5 A, a
number ofthese devices is connected in parallel,under the control
of a single voltage set-ting circuit. The result is a
surprisinglysimple PSU, which, in its basic version, iscapable of
providing an output current ofup to 10 A.
The present PSU is ideal for chargingbatteries, for experiments
with a widerange of electronic circuits, and for usewith high
-power transistorized RF ampli-fiers.
Design backgroundBefore discussing the circuit in detail, it
is
worth while looking at the basic operationof the LNI317.
The LN(1317 is a three -pin integratedhigh -power voltage
regulator which maybe used in a 'floating' circuit. As shown inFig.
1, a voltage of 1.25 \ e\i'zts betweenthe output and the ADJLsr
input. Providedthe output current is 5 mA or greater, andthere
exists a sufficiently high voltage dif-ference between the input
and the output,the internal control circuit will maintainthe 1.25 V
voltage difference between theoutput and the adjust input.
Evidently,this voltage disappears when the chipswitches off owing
to a thermal overload.condition.
Since the regulator may be used in a'floating' circuit, it is
possible to set theoutput voltage by raising the potential atthe
ADJUST input with the aid of a voltagedivider between the output
and ground asshown in Fig. 1. The constant voltage of1.25 V across
R1 causes a constant currentthrough RI and R2 (disregarding, for
themoment, the small current supplied by theADJUST terminal). In
this configuration,
MAIN SPECIFICATIONS
Output voltage:
Output current:
4-20 V
10A(basic version)
Current limiting:
Thermal protection:
Ripple rejection:
Operating temperature:
internal
internal
>80 dB
0-50 CSimple to extend for higher outputcurrents
Separate voltage and current indica-tors
the output voltage, U, is determined bythe ratio of Rt and R2.
The output voltagerises when R2 is increased. When R2 ismade 0 S2,
the output voltage equals thereference voltage of 1.25 V. In the
form ofan equation:
Or
1.25 = (R1/ (RI + R2))
= 1.25 (RI + R2)/ R1)
It will be clear that when a number ofregulators are connected
in parallel, theoutput current must be distributedequally. This may
be achieved as shownin Fig. 2 by fitting a small resistance,
Rs,
0SL,n45 12
0
Fig. 1. Lt.1317 in basic regulator circuitwith adjustable output
voltage.
ELEKTOR ELECTRONICS .R tX AL GUST 1990
-
20 GENERAL. INTEREST
Fig. 2. Principle of parallel -connectedU.1317s with series
output resistors to en-sure equal current distribution.
in series with each regulator output. As-suming that Rs«R 1, the
operation of thetop voltage regulator in Fig. 2 is expressedby:
L25 = Uo (Rt /(R1 +R2)) + 10 R.
and that of the one below by
L25 = Llo (RI / (Ri +R2)) + 11 R,
Since the equations are identical with theexception of the terms
I. and II, these cur-rents must be equal. The equations alsosuggest
the use of more than two regula-tors in parallel, since the output
currentdistribution is, in principle, determinedby two tolerance
factors only: first, thereference voltage of the LM317s used,
andsecond, the values of resistors R,_
Unfortunately, connecting LM3I 7s inparallel is not so simple in
practice,mainly for two reasons. First, the voltagedrop across
resistors R., is dependent onthe output current, so that the
regulatorscan not keep the output voltage constant.This is so
because they will attempt tokeep the voltage across the series
combi-nation of RI and Rs at a constant level ofL23 V. The upshot
is that the voltage atthe supply output (i.e., behind resistorsR,1
will drop when the output current
Fig. 3. LM317-based series regulator withactive, external,
voltage setting.
rises, since this means that the drop acrossresistors Rs. rises.
Second, small differen-ces between the reference voltages of
theregulators will result in unequal currentdistribution.
External voltage regulationFigure 3 shows the basic circuit of
an ex-tended voltage control circuit connectedto the LM317. For
simplicity's sake, it isassumed that the power supply containsonly
one L\.1317.
The -input of the opamp (a Type 741)is held at half the supply
output voltage,LI., with the aid of R4 -R5, while the +inputis held
at a reference potential. This refer-ence is obtained from a
constant currentthrough resistor R3 and preset Pt. Thisconstant
current is obtained from a resis-tor connected between the output
and theADJUST input of the regulator. Since the
From theory to practiceAfter the above description of the
basicoperation of the power supply, little re-mains to be said
about the circuit diagramin Fig. 5.
The mains transformer, Tri, is a toroidtype with two secondary
windings of15 V/7.5 A each. The current specificationis not
obligatory, however, and may begeared to the anticipated loads. In
anycase, the transformer output current mustbe greater than or
equal to 1.4 times themaximum anticipated load current of thepower
supply.
Although most high -power toroidtransformers have two secondary
wind-ings which may be connected in parallelto boost the output
current, it is better inpractice to fit each secondary windingwith
its own bridge rectifier and associ-ated reservoir capacitor.
Fig. 4. Completed 10-A regulator board with heat -sink. and
voltage control board.
regulator maintains a constant voltage(1.25 V) between these
terminals, R3 andPt draw a constant current via a
transistor,Ti.
Because the opamp is a difference am-plifier, it will attempt to
regulate its out-put voltage until its inputs are at equallevels.
Transistor Ti is, therefore, drivensuch that the voltage across R3
and Ptequals half the supply output voltage.This means that the
changing resistanceformed by the transistor causes the volt-age at
the ADJUST input to rise, and with itthe output voltage of the
supply. Thiscloses the control loop. In the circuitshown in Fig. 3,
preset Pt forms the out-put voltage control because it
determinesthe voltage at the +input of the opamp.
The high currents that may have to besupplied by the bridge
rectifiers force theuse of adequately sized heat -sinks forthese
devices. As a rule of thumb, thereservoir capacitors must be 10,000
1.1Feach per 10 A of output current. When thesize of your enclosure
allows it, this is bestincreased to 20,000 !IF per 10 A.
Provided the reservoir capacitors aresufficiently large, a
secondary voltage of15 VAC will provide an output voltage ofup to
12 VDC. Similarly, a transformervoltage of 18 VAC allows the
circuit tosupply up to 15 VDC. A maximum outputvoltage slightly
lower than 28 V may beobtained by using a transformer with two24-V
secondary windings and reservoircapacitors rated at 63 V. Note that
a 33-Vtransformer must not be used since it
ELEKTOR ELECTRONICS JULY AUGUST 1990
-
COMPACT 10-A POWER SUPPLY
U4317
K1
Trl
healsink
printed circuit board 1
- B1
7A 5
, re: Ao IC8 01
LM317
R13
I Id
0++-f3++
IC7LM317
all.
/ I
111
1
3W
R52
106LM317
adi.
3W
an
105LM317
3W
I
CIC=I
00014 25Y
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0
C2CI100005 255
51. 52 = B80C10 000
printed circuit board 2
IC4LM317
./I
/I111
1
3W
R9
0 1C3 R8
LM317 I
J
0
R2
TI
3W
_
C C141P2 R6`III MN
Ik
H
BC161
25V
R3
6
1N4148
INiatt
R4
IC1
7 2
LM741
H
PI14
R?
CtO471, 25Y
P3 ,474
1.4
- - - -Si.,Z075.11
Fig. 5. Circuit diagram of the power supply (basic version with
one regulator board for an output current of 10 A).
would cause the maximum input voltageof the circuit to be
exceeded.
Two moving -coil meters are includedin the circuit, one for
voltage measure-ment and one for current measurement.These meters
may be replaced by digital(LCD) read-outs, which are available
asready-made modules. Two such modulesare used in the prototype of
the powersupply. Their one disadvantage is thatthey require a
floating power supply. Thesimplest way to avoid problems with
thissupply is to power the modules from twoseparate 9-V batteries.
To save batterypower, an optocoupler circuit may beused to enable
the power supply to switch
the modules on and off. The basic circuitto realize this type of
control is shown inFig. 8. Alternatively, construct a
small,separate, power supply for the LCD mo-dules.
Most LCD modules are 200 -mV volt-meters. Fortunately, they are
easily con-verted into 100-uA ammeters as requiredhere by shunting
the input with a 1-k0resistor.
ConstructionFigure 6 shows the two printed -circuitboards You
need to build the power sup-ply: one holds the seven regulators
and
their associated power resistors, the other,a much smaller type,
the voltage controlcircuit.
All components, with the exception ofthe mains transformer, the
bridge recti-fiers and the reservoir capacitors, are ac-commodated
on the two PCBs. The sevenregulators are fitted on the heat -sink
in amanner that allows them to be soldereddirect to the printed
-circuit board asshown in the photographs. Each regulatormust be
electrically insulated from theheat -sink. In the prototype, 1.5
-mm thickceramic insulators are used instead of themore common mica
washers for reasonsof safety and mechanical stability.
FLEKTOR ELECTRONICS JULY/AUGUST 1990
-
GENERAL INTEREST
PNociireurahfro.:\m-jiAir.\0
000A
ICE 000 IC7 0 0 0 ICE
r
6
Its .0cc0c0
o -61 IC5
P3
000
a
0 -{E16 -K)
01:
C3-40
IC4 0-00-
0 A 0000
103
0
O 0ccCO
Fig. 6. Track layouts (mirror images) and component mounting
plans of the two boards that go into the making of the 10-A power
supply.
COMPONENTS LIST
Resistors: Semiconductors: 1 toroid mains transformer Tn7 01222
3W RI:RS-813 1 1N4148 2x15 V'7.5 A e.g. ILP1 10052 R2 1 8C161 Type
63013 (240V mains)1 15012 R3 1 741 ICI or 61013 (220V mains)
2 4k7 R4;135 7 11.4317 (S0-220 enclosure) IC2-ICS 7 Insulating
washer for LM317
1 1k5 R6 1 Heat -sink 1 KW: e.g..
1 82k2 1k0 preset H
R7
Pi:P2Miscellaneous:2 100pA f.s.d. moving -coil M I ,M2 1
Fischer SK120SA100printed -circuit board 900045-1
1 47k preset H P3 meter, or two 200 -mV LCD 1 printed -circuit
board 900045-2
voltmeter modules 1 enclosure e.g.. Tetet
Capacitors: 2 B80C10000 B1;132 Type LC1050
2 10,000pF 25V1 10µF 25V1 47µF 25V
C1;C2C3
C4
1 Mains appliance socketwith built-in switch andfuseholder
KI
1 100n CS 1 Fuse 3.15 A slow Fl
ELEKTOR ELECTRONICS JULY AUGUST 1990
-
COMPACT 10-A POWER SUPPLY
Fig. 7. Wiring diagram of the power supply. Use heavy-duty
insulated wire as indicatedby the heavy lines.
Fig. 8. Power supply and automatic on'offcontrol for the LCD
-based V,l read-outs.
The.population of the two single -sidedprinted circuit boards is
not expected tocause problems. Mount the power resis-tors on the
regulator board at a height ofabout 3 mm above the PCB surface.
The completed boards are fitted in asturdy metal enclosure as
shown in thephotographs of the prototype. A clearanceis cut in the
rear panel to enable the heat -sink with the attached regulators to
befitted.
The mains on/off switch is purposelynot fitted on the front
panel to avoid wiresinside the enclosure that carry the
mainsvoltage. Figure 9 illustrates the use of amains socket with
integral fuseholder andon/off switch fitted in the rear panel of
theenclosure. The supply output terminalson the front panel are
heavy-duty wandersockets.
Fig. 9. Close-up of the rear panel assembly. Note the mains
socket and the clearance cufor the heat -sink.
The thick lines in the wiring diagramin Fig. 7 show the
connections that mustbe made in heavy-duty insulated wire. Allother
connections are made in medium -duty insulated wire. Do not forget
to con-nect the output terminal to the '0'terminals on the two
boards. The heavy-duty wires are best connected to the PCBsvia
spade terminals and mating sockets asused in cars. When this is
done, the outputvoltage of the supply will remain constanteven at
heavy loads. Our prototype wastested in this respect and found to
degradeby only 60 mV when the load was in-creased from 0 to 10
A.
Need more than 10 A?The power supply may, in principle,
beextended with as many regulator boardsType 900045-1 as required
for a particularmaximum output current. Each addi-tional regulator
board increases the cur-rent by 10 A. If that is too much, simply
fitone regulator per 1.4 A of additional cur-rent. The construction
of the additionalregulator boards is identical to that of thebasic
version described above. They aresimply connected in parallel by
intercon-necting corresponding terminals, exceptterminal 'B', which
is connected from oneboard 900045-1 only to the
correspondingterminal on board 900043-2.
AdjustmentSwitch the supply and on adjust Pi untilthe output
voltage is 10 V. Next, connecta load (e.g., a 12-V car lamp). Use a
digitalmultimeter to calibrate the current meterby adjusting P:,
and the voltage meter byadjusting P3.
Note that when the supply is notloaded, the LM317 with the
lowest refer-ence voltage will supply the output volt-age. In this
condition, it may happen thatcurrent flows into the outputs of the
otherLM317s, causing the current meter to in-dicate a negative
value. This is normal.however, and no cause for concern.
ELEKTOR ELECTRONICS JULY AUGUST 1990
-
24
INMARSAT'S STANDARD -CB. Higgins
International Maritime Satellite organisation (Inmarsat) are
nowmarketing a package of satellite -based communications services
to
the business community generally. This article provides
anintroduction into the technical aspects of these services.
Inmarsat uses geostationary satellites inthe three geographical
regions of the At-lantic (AOR). Pacific (POR) and IndianOcean (IOR)
regions. For each region aworking pair (known as a dual) and
onespare satellite are employed. An over-view of the currently used
nine satellitesis given in Table I. It should be notedthat Inmarsat
plans to widen the AtlanticOcean coverage towards the West. mov-ing
the \tarecs B2 satellite from 26° \Vto 55.:;\V.
What is Standard -C?Standard -C is a satellite -based data
com-
munications system that operates at aspeed of 600 bit per
second. Data. in theform of computer output. or the outputof
various telemetry systems on boardcraft and vehicles, can be sent
to a basestation from almost any location onearth.
Standard -C is a message -based sys-tem. i.e.. the sending
equipment must'pack' its data for each individual trans-mission.
Once formatted. the data pack-age ('packet') is stored in a
messagebuffer until a suitable time slot is ob-tained on the
satellite. The message buff-er has a single packet .capacity of32
KBytes.
Standard -C \ stems on board craftand vehicles are made with
connectionsvia an RS -232 port to allow for easyinterfacing with
data equipment such aspersonal computers. terminals. data log-ging
systems. etc. functioning as DCE(data circuit terminating
equipment)and/or DTE (data terminal equipment).
Two main categories of service arepossible in the Standard -C
stem:
store -and -forward message transferend -to -end services
Store -and -forward message transfer in-volves the formatting of
complete mess -
COAST EARTH STATIONStore and Forward
Message Switch
TELECOMMUNICATIONS NETWORK
TelexVoice Band DataLeased LinesTeletexElectronic Moil
Packet SwitchedData NetworksLettergrom ServiceX.25X.400
PUBLIC NETWORK
per
0 0 CLOSEDUSERGROUPS
ma Weiwigs
oft II NagOMR'
11.
111114
thesimai
Fig. 1. Coast earth station (CES) acts as a store -and -forward
message switch on to the satellite link (illustration courtesy of
Inmarsat).
ITLEKTOR ELECTRONICS JULY/AUGUST 1990
-
ages at the coast earth station or the shipearth station before
transmission overthe satellite channel. The (telex) mess-ages are
then transmitted to ship or toshore on a simplex basis when
capacityis available.
End -to -end services require a perma-nent or semi -permanent
circuit to be es-tablished from the coast earth station tothe
appropriate terrestrial facilities forthe duration of the (telex)
connection.
All other services provided by Stand-ard -C are optional. These
services in-clude ship -to -shore half -duplex circuits.full
-duplex circuits, polling, individ-ually -directed. group -directed
and area -directed calls, and automatic datareporting.
Standard -C uses radio frequencies inthe L band and C band
sections of thespectrum as shown in Table 2. Incre-ments of 5 kHz
are used throughout thebands.
ManufacturersAround the world, interest is beingshown by
manufacturers of electronicequipment to produce Standard -C
com-patible communications sets for use atcoast -earth stations and
on board ships.vehicles and, recently. aircraft.
STC International Marine based atMitchem in the UK produce
equipmentcalled Mascot C that is designed for allsizes of shipping
vessels. Denmark -based Thrane & Thrane make systemsfor use in
and on land -mobile vehicles.Table 3 shows the major equipment
ma-kers and the names of their products.
The SES: antennas and RFconsiderations
All manufacturers of ship earth stations(SES) use
omnidirectional antennas intheir systems. as this eliminates the
needfor the user to re -adjust for ever\ trans-mission or
reception.
INMARSAT'S STANDARD -C
Fig. 2. Intelsat -V -F1 satellite undergoing tests in an
anachoic chamber.
Antennas used in the Standard -C sys-tem must be installed at
least 5 m awayfrom C -band radar equipment. For X -
Region Longitude
AOR 26=1N
AOR 18.5=IN
AOR 15°W
IOR 63=E
IOR 60'EIOR 73=E
POR 180°E
POR 177.5'E
Satellite Use
Memos 82 operationalIntelsat -V (MCS) dual
Marisat Fl spare
Intelsat -V (MCS) operationalIntelsat -V (MCS) dual
Marisat F2 spare
Intelsat -V (MCS) operational!.larecs A dual
Table 1. Satellite positions and earth coverage.
band radar. the minimum distance ismuch smaller.
Antenna designs vary from manufac-turer to manufacturer. Special
designshave been adopted for use on differenttypes, of sea vessel
and on land basedvehicles. One innovative design stili tobe tested
is a flat circular antenna thatcan withstand an automatic car
wash.
Power levels in the standard -C sys-tem are low compared to.
say. satellite -TV. This is mainly because of the muchsmaller
bandwidth requirement (typi-cally. about 1 MHz instead of 27 MHzon
a satellite -TV transponder). Circularpolarisation is used to
reduce the effectsof Faraday rotation in the uplink anddownlink
paths to and from the satellite.Althoueh the antenna gain pattern
is not
ELEKTOR ELECTRoNICS JULY" AUGUST 1990
-
26 CONIMUNICATIONS
ACTUATOR
DCP
DATA TERMALECUPMENIT
(DTE)
N I -AFACE 4AND CONTROL
INT
LEVEL
FLOWMETERTEMPERATURE
GASESCONDUCTIVITY
PRESSLP.E
Fig. 3. Schematic diagram of Standard -C interfaces for remote
data collection and control
Use Up Down link Frequency Radio band
Coast earth station up 6 GHz CCoast earth station down 4 GHz
CShip earth station up 1.6 GHz LShip earth station down 1.5 GHz
L
Table 2. Band frequency assignment for Inmarsat Standard -C
communication links.
Country Manufacturer Equipmentname
Denmark Thrane & Thrane TT -3020AFrance SNEC STC 01Japan
Japan Radio Co. JUE 65AUK STC International Mascot C
Marine
Table 3. Standard -C equipment manufacturers.
directly specified. provision must bemade. e.g.. 1t ith a
gyroscope. to ensurethat the minimum EIRP and GfT figuresare met
down to -15' to cope with shipmotion. Table 4 shows some typical
RFequipment parameters.
Out at sea...s Inmarsat is mainly concerned with
maritime aspects of communication.equipment designed for the
system hasto conform to the rigours of operating atsea. Therefore.
specifications alwayshave a strong leaning to
environmentalconditions such as temperature. hu-midity and
vibration-see Table 5.
Coast earth station
The link between the Inmarsat systemand communications companies
of vari-
220 220 3:: 320 34: 20 £3 50 100 120 143 150 180 2c,0 220
240
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11111111111111.____-....___ __ --
GOONHILL . '4, \, SARYDESSA ' 1%., 1
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I OUTHBURY8 ITR 0
ATA0 #10PYLAE RAH
!BARAK!FUCA YAMAGU H SANTA P
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1.14U- KARACHI
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FDA ARV I -tN
SINGASOR
TANGUA
2ALCARCE
U
583
trie 873
11414
4.582fir 872
28: 220 34: 0 20 43 :0 '20 '40 750 .20 2:: 220 240-AL OCEAN
REGION CODE (TELEX) ear OCEAN REGION CODE (TELEPHONE)
SATELLITE LOCATION, ACRE 18.5°W, IOR 636E. POR 180°E, AORW 55°W
COAST EARTH STATIONS AIN OPERATION OPLANNED
0
Fig. 4. Overview of frequencies used for Standard -C
communications between vessels, satellites and coast earth
stations.
ELEKIOR ELECTRONICS JULY AUGUST 1990
-
INNIARSAT'S STANDARD -C
Parameter TT -3020A
Antenna polarisation RHCEIRP (at 5' elevation) 12 dBW
(min.)Figure of merit GiT -23 dB,K(at 5- elevation)
TX frequency band 1.6265 - 1.6465 GHzRX frequency band 1.530 -
1.545 GHz
JUE65A
RHC
14 -z2 dBW
-23 dBiK
1.6265 - 1.6465 GHz1.530 - 1.545 GHz
Table 4. Some antenna unit specifications.
ous countries is all-important for the im-plementation of the
complete Standard -C system.
Figure 3 illustrates how the coastearth station fits into the
total system. It
acts as a store -and -for ard messageswitch to the satellite.
Operating. on C -band (i.e., 4/6 GHz). the link to the sat-ellite
is less susceptible to atmosphericinterference as a result of
problematic
weather conditions.Developments are continuously tak-
ing place in coast earth station technol-ogy. For example.
Thrane and Thranehave recently been ax% arded contracts bySingapore
Telecom and Telecom Den-mark for the supply of equipment forcoast
earth stations in the respectivecountries.
Further information on the Standard-C communications system may
be ob-tained fromInternational Maritime Satellite Or-ganisation
(Inmarsat) 40 MeltonStreet Euston Square LONDONNW1 2E0.
Parameter
Temperature (electronics)
Temperature (antenna unit)
Humidity
Ice
PrecipitationWind
Vibration (electronics unit)
Vibration (antenna unit)
TT -3020A
O'C to 45:C (operating)-20:C to 70 C (storaae)-35: to 55'C
(operating)-40:C to 70=C (storage)95% non -condensing
up to 2.5 cmup to 10 cm,hrup to 100 knots2-15.8 Hz at 1 mm
peak'15.8-100 Hz at 1.0 g peak acceleration2-10 Hz at 2.54 mm
peak10-100 Hz at 1.0 g peak acceleration
JUE-65A
0=C to 45'C
-35:C to 55'C
up to 95% at 40:C
2 to 15.8 Hz at 2.54 mm peak15.8 to 100 Hz at 1.0 g peak
acceleration2-10 Hz at 2.54 mm peak10-100 Hz at 1.0 g peak
acceleration
Table 5. Environmental specifications of two types of Inmarsat
Standard -C SES (ship earth) stations.
NATIONAL ANDINTERNATIONAL NETWORKS
Fig. 5. Inmarsat satellite coverage at 0 and 5 degrees elevation
above the horizon. The illustration shows the three ocean regions,
AOR,POR and 10R, ocean codes and locations of coast earth stations
(illustration courtesy of Inmarsat).
ELEKTOR ELECTRONICS JULY AUGUST 1990
-
28
HAND-HELD 8 -CHANNEL LOGICANALYSER
The new TA -100 from Thurlby-Thandar is alow-cost logic analyser
that replacesmultiple logic probes or logic checkers. andcan be
substituted for more complex logicanalysers in many
applications.
The TA- 100 has eight data inputs. an exter-nal clock input, a
trigger input and a triggerchaining capability. Maximum clock
fre-quency is 25 MHz. and data pulses less than10 ns wide can be
captured and displayed.The trigger circuits of up to four pods
can
be linked together to expand the trigger rec-ognition to up to
32 channels. Each channelof the trigger word can be set to 0. 1 or
X(don't care). The logic status of each channelis continuously
shown on a LED display. andpulse -stretching enables short pulses
andhigh frequencies to be clearly displayed.
The TA -100 is priced at £89 (plus VAT).
Thurlby-Thandar Ltd. Glebe Road HUNTINGDON PE18 7DX.
Telephone:10480) 412451. Fax: (0480) 450409.
NEW PHOTODETECTOR RANGEFROM CENTRONIC
Centronic have launched a new ranee ofphotodetectors. the 0S135
series. The newrange of devices has a photodiode mountedtogether
with an amplifier in a hermeticallysealed TO8 package. and
incorporates a low -profile cap.
The new photodetectors are claimed to sim-
i\ EW PRODUCTS
design by eliminating the needfor a head amplifier. Applications
includeoptical instrumentation. colour coding. am-bient brightness
control. alarm systems andflow meters.The detectors are available
in four ver-
sions. tailored to operate within the follow-ing wavelength
bands: ultra -violet(250-400 nm), visible (400-900 mu). infra-red
(600-1100 nm) and for eye -response de-tection.
Centronic Ltd. Centronic House KingHenry's Drive New Addington
CROY-DON CR9 08G. Telephone: (0689) 47021.Fax: (0689) 45117.
LOW-COST 31/, -DIGIT LED PANELMETER
Autona's low-cost DVM module has anoverall depth of only 11 mm.
which allowsit to be built into the most compact of
equip-ments.
Introduced as the DVM 456. the unit fea-tures 0.56 -inch high
-efficiency displayswhich, [(nether with the red filter in
themoulded bezel (supplied with the unit). pro-vides a display
which is readable under highambient light conditions.
An on -board supply stabiliser simplifiesinstallation into a
wide ranee of equipment,since the module operates from an
unregu-lated supply of 7-12 V. whilst protectionagainst input
overload and reverse polaritysupplies ensure safe operation in
hostile en-vironments.
Available in a standard form with a basicsensitivity of ±L999 V.
the unit may be sup-plied with alternative f.s.d.
specificationswhere quantity requirements exist.
Supplied with a comprehensive, data sheet.the unit is priced at
£19.95 (plus VAT) forsingle quantities.
Autona Ltd 51 Poppy Road PRINCESRISBOROUGH HP17 9DB.
Telephone:(084 44) 5740. Fax: (084 44) 7102.
TR_t\SPARENTSATELLITE DISHGETS GREEN VOTE
Zeta Services have recently introduced atransparent glass
satellite dish designed toovercome environmental objections to
un-sightly metal and fibreglass alternatives.
The patented 60 -cm see-through dish,CrystalVision. is made from
Armourplatemetal -impregnated glass that has the samereflective
qualities to microwaves as stand-ard metal dishes.
The electronics for the CrystalVision dishare supplied by
Marconi. and the whole unit.which is the same size as the smallest
Astradish. is mounted on a clear polycarbonatebase plate for
unobtrusive installation. Pro-duction of the glass dish is expected
to startlate summer for autumn delivery at a priceclaimed as
slightly higher than opaque metalor fibreglass options.
Zeta Services Ltd. Harden Park Alder -ley Edge CHESHIRE SK9 7QN.
Tele-phone: (0625) 583850. Fax: (0625) 585282.
NEW SERIES COMPACT 15-75W DC -DC CONVERTERS
A new series of DC -DC converters, desig-nated 700 Series, has
been introduced byIntrOnics Inc.. U.S.A.
There are six models in the ranee offering5 V. 12 V and 15 VDC
single outputs at 3 Ato 5 A (remote sense and remote control
arcstandard on the 5-A models). The voltageinput range varies from
8-40 VDC to 18-40 VDC depending on the specified outputs_All models
operate at 40 kHz (typ.) arid from-25'C to 70°C with derating. The
storagetemperature is specified at -40°C to 105°C.
Important features of the new supplies in-clude ultra -wide
input voltage range. effi-ciency of up to 90g. thermal
overloadprotection, low thermal gradient and reversepolarity
protection.
Measuring just 3x2.5x0.81 inch. theDC700 series are all copper
encased for six -sided shielding and are pin -compatible forPC
board mounting. They are suitable forapplications in
telecommunications. processcontrol systems and battery -operated
sys-tems.
Pascal! Electronics Ltd. Saxon House Downside
SUNBURY-ON-THAMESTw 16 6RY. Telephone: (01 979) 0123.Fax: (0932)
782402.
ELEKTOR ELECTRONICS JULYiAtGUST 1990
-
all ICs on the controls board. Switch onand check that the LEDs
light in a certainpattern (depending on the software ver-sion).
When the processor works, the LEDdisplays indicate a start-up code.
Possiblesources of failure: incorrect connection be-tween main
board and controls board;empty EPROM; LEDs fitted the wrongway
around, short-circuited PCB tracks;bad IC socket(s); faulty
component.
Switch off. Insert the remaining ICs intheir sockets, then
connect the keyboardvia the 40 -way cable- Switch on. The start-up
code (software version number)should appear on the display. Connect
aMIDI expander (set to ON INI mode) to theMIDI output. If
everything is all right sofar, it should produce notes when youplay
on the MIDI keyboard. If not, reversethe 40 -way keyboard
connector. Possiblesources of failure: incorrect keyboard
con-nection; short-circuited PCB tracks; faultyMIDI cable; wrong
MIDI channel on ex-pander; faulty component_
MIDI MASTER KEYBOARD
PART 2: TESTING AND PROGRAMMING
D. Doepfer
In this second and last instalment we check the operation of the
twoprinted -circuit boards, help you on your way in faultfinding
(if
necessary) and last but not least discuss the various
programmingand menu options offered by the microprocessor
-controlled
operating system running on the keyboard.
Even experienced electronics constructorsshould not fit the
completed printed -cir-cuit boards in the keyboard enclosurewithout
a thorough functional check_First, inspect the boards visually,
lookingfor short-circuits and bad solder joints.Once again refer to
the component over-lay and the parts list to make sure that
allcomponents have the right value andorientation. Test all
flatcables by checkingthe continuity of every individual wire.
Connect the two boards via the 16 -wayflatcable, observing the
polarity of the1DC sockets. If applicable, remove all in-tegrated
circuits from the boards. Applypower, and check the presence of +5
V atall relevant points (consult the circuit di-agram). Possible
sources of failure at thisstage are the mains adapter, the 7805 or
itsassociated smoothing capacitors, a defec-tive tantalum
decoupling capacitor, or ashort-circuit between PCB tracks.
Switch off the power, and insert ICI,IC2 and IC3 into their
sockets, followed by
MIDS-MASTERKEYBOARD
Lint11\72IMete-
0r r I
When the previous tests check out, thehardware is likely to
function correctly_Note, however, that errors like a stuck keymay
not come to light until later.
Testing the modulationwheelAs already noted in the description
of themodulation wheel function, the mechan-ical end stops of the
potentiometer do notallow this to cover the full turning rangeof
270°. Although this is taken into ac-count by the control software,
the periodof the VCO signal (IC4) should be made tolie in the range
between 4.2 ms and 8 ms_The actual limits are 4096 us and 8192
is.Values outside this range produce erro-neous control values.
The range limits are simple to adjustwith the aid of a period
meter or a fre-quency meter: alternately adjust Pt (span)and
operate the modulation wheel (peri-od) until the above range is
achieved.
In case such test equipment is notavailable, the modulation
wheel may alsobe adjusted with the aid of routine 1 orroutine 2
provided by the keyboard con-trol software. These routines enable
themicroprocessor to send the MIDI controldata obtained from the
modulation wheelto the LED displays in two different ways.
Routine 2 is invoked by keeping the sec-ond key to the left in
the upper rowpressed while the keyboard is switchedon. The displays
indicate the measuredcontrol data in hexadecimal (00-FF).
Thecorrect range is achieved by alternatelyadjusting PI (parameter
span) and opera-ting the modulation wheel (actual par-ameter
value). Set a sufficiently largerange to allow for wear and tear,
compo-nent tolerance, and drift owing to mech-anical strain.
Remember that the softwarecaters for the reduction of the full
range(00-FF) to OF -FO to cover the requiredMIDI range of 00-7F.
This means thatMIDI parameter value 00 is sent when themodulation
wheel supplies a value smal-ler than OF. Similarly, 7F is sent when
the
ELEKtOR ELECIRuNICS t_(tsT 1990
-
30 ELECTROPHON1CS
,--! N CI F? :4 C9.07")' 1:3 7- C'i In CO CO ° .'j C-.3 L'" N -
CO 0C,4 Cs.ICN: 7,,N ir)N t!'N CPCsj 001 CqCOBank Nr.
930339 -II- I
Fig. 7. A number of keys on the musical keyboard are used in
conjunction with the control software to enter menu options and
settings.
value exceeds FO. Hence, a range settingof, say, 0A -F2 is
perfectly adequate.
Routine 1 is invoked by keeping the ex-treme leftmost key in the
upper rowpressed while the keyboard is switchedon. It enables the
processor to indicate thetransmitted MIDI parameter value, i.e.,the
control data sent to the MIDI instru-ment after averaging and
proportioningvia a look -up table in the control program.Obviously,
the range of this indication is00-7F, corresponding to the
permissiblerange of MIDI parameter values. When aself-adjusting
modulation wheel is used,its rest position should produce a
displayreading of 40 (64 decimal), irrespective ofthe side from
which it arrives at the restposition. If necessary ensure this
centrevalue by carefully re -adjusting Pi andchecking the range
limits with the aid ofroutine 2.
In the pitch -bend mode, the softwareprovides an automatic
correction functionthat subtracts or adds a certain value togive a
range where only 40 is produced atthe centre position of the
modulationwheel. In case a steady value can not beachieved, fit a
2.2 tiF tantalum capacitor(Cu)) between the control voltage
sup-plied by the potentiometer and ground.An instability of ±-1
digit is allowed be-cause it is compensated by averaging
andthreshold detection routines in the controlprogram.
After the above adjustment, carefullytighten the nut on the
modulation poten-tiometer, making sure its setting is notchanged.
Switch on the keyboard (with-out invoking either of the test
routines)and check the correct range and functionof the MIDI
control parameters.
Programming functionsMost of the functions provided by theMIDI
master keyboard are selected withthe aid of the programming keys on
thefront panel. These keys work in conjunc-tion with a menu, the
control of whichrests with the microprocessor and the
soft-ware.
Connect either one of the MIDI outputsof the keyboard to the
MIDI input of anexpander synthesizer, sequencer or sam-pler.
Connect the foot switch to the key-board via the jack socket. When
soprogrammed and actuated in a particularkeyboard zone, thiS foot
switch forms aSUSTAIN pedal. Do not connect or dis-connect the foot
switch with the keyboardswitched on.
Apply power. The LED displays indi-cate the software version
number (e.g.,100), and the LEDs should light up briefly.Next, the
display indicates 'PLA' for PLAYmode. At this stage, PRESET 1 is
used.
The menu has the following eight options:presetprogram
change/real timesplitchanneltransposedynamiccontrollerspanic
which are selected by the eight associatedkeys. The current
option is indicated by aLED. In the PLAY mode, no LED lights.
Insome menus, the keyboard keys are usedin addition to the control
keys to set cer-tain parameters. Also note that somemenus return
automatically to the PLAYmode after the parameter has been set.Most
menus, however, can be left only bypressing another menu key.
In all menus, except PRESET and PANIC,the next keyboard zone is
selected bypressing the same menu key once more(note: the
boundaries of a zone are markedby splits). Therefore, press the
menu keyas many times as required to arrive at acertain zone. The
selection is cyclic: i.e.,zone 1 follows zone 4.
With some functions, the displaysbriefly shows a letter- or
number -se-quence before returning to `PLA'. Duringthese sequences,
however, the play modeis active. The indication period before
thedisplay switches to 'PLA' allows set par-ameter values to be
read off easily.
Figure 6 shows which keyboard keys
are used in conjunction with the menukeys to set certain
parameters. As shownin Fig. 7, the white keyboard keys in thelowest
octave are assigned the followingfunctions:
Bank 1-4 (C; D; E; F)Start (G)Stop (A)Continue (B)
The number keys start at the next higheroctave, i.e., C=1; C#=2,
D=3, D#=4; etc. forall number entries required (programnumber,
channel, dynamic response table,control code, etc.)
PRESETThe EPROM contains 16 presets, any oneof which may be
selected by the user as thebasic keyboard setting. Each preset
con-tains data on each of the four zones, theMIDI channel,
transposition, assignmentand actuation of control data, and the
vel-ocity table. The currently selected presetis indicated on the
LED displays for acouple of seconds- before the keyboardgoes to
PLAY mode as indicated by theletters `PLA'.
PROGRAM CHANGE/REAL TIMEThis menu allows the programs runningon
the connected MIDI equipment to bechanged. It is used together with
key-board keys to send PROGRAM CHANGE com-mands and, with certain
keys only,real-time .MIDI commands START, STOPand CONTINUE.
The selected zone is shown to the lefton the read-out, while the
current bankappears to the right. The zone indicationis important
for the MIDI channel onwhich the PROGRAM CHANGE command issent.
The programs are organized in theform of 4 banks of 32 numbers
each.Bank 1 contains program numbers 1-32,bank 2 program numbers
33-64, bank 3program numbers 65-96, and bank 4 pro-gram numbers
97-128. The banks are se-lected by the first four keys on
thekeyboard (see Fig. 7). When a bank num-ber is changed, the new
number is shown
ELEKTOR ELECTRONICS JULY/AUGUST 1990
-
MIDI MASTER KEYBOARD PART 2
Fig. 8. Software -selected dynamic response curves. A linear
response (curve 'a') oftengives the impression that the dynamic
characteristic can not be set with sufficient accuracyin the low
-volume ranges. This may be compensated in three steps by response
charac-teristics 'b', 'c' and 'd'. Curve 'e' provides the inverse
effect, giving greater resolution in thehigh -volume ranges. Curve
'f' is exponential with a certain low -volume off -set. The
inversecurve, 'g', gives a smaller dynamic range at greater key
velocities. This response isparticularly suited to velocity
-controlled mixing effects: one zone is assigned a normalresponse
(e.g., 'c'), and another zone, of equal size, the inverse response.
These two zonesare used to control two MIDI channels
simultaneously, e.g., on two expanders, or on oneexpander capable
of generating two sounds on two different Channels. The key
velocity thenallows you to switch between these channels as you
play. Curve 'h', finally, producesvelocity parameter '64'
irrespective of the key strike force. This response is
particularlysuited to non -dynamic sounds, e.g., those