IMG_0002

SIMPLE AUTOMATICWAIeR-LEvEL coNTRoLLE Rg SUNIL KUMAR

ater-level coutrollers are

.orlunon nowadavs.'fhe..: r)ri{1. . dlsr:':ib rr,l h (:rire i:

minal Vcc is at the bottom of the tank,

sensor tertninal L is just above tltz:

b()ttom of tlre tank :rrtd st'nsor tcrmi-nal H is at the toP of thc tank. Ath:r

- v.-u. lt-alt B1q,'.rcrly ins.tir!lsr1 lllil ':1'.-

sors in the OHT ar:d cor.necled the

porver sr-rpply, the circuit is readl' to

Ll se.

Since Vcc terminal is at thc'l;ottom

-f thc ti..nk, vvhen thr-' x'ater lcvel falls

la), RL1

energises and

the motor starts

filling rvatcr irr

the tank.'Ihen1otor remains

'ort' eveu rvhet:

a1'a,!g:_lqyg:l:]'osscs selr.sor

the tank

L.

As lvater inrises to

touch seusor H, trmer lC2 is Lc-

triggered at pin 6 via irrvet'ters N3

and N4 ancl as a t'esitlt, its output

goes lon'. 'lhe relay de-energises ancl

the nrotot' stops filling rvater iu the

tank. The motor renrai;rs 'off' even

when the water level fails belorv sen-

sor H.As water is consunrecl and its level

falls below sensor L, the mobr restarts'l'hereafter; the cYcle rePeats.

Yott can also manuallY start and

stop the motor nsing swiich 51. o ,

iliveq,t

br:lorr' scnsor L,

time,: IC2 is

triggere,J at pin2 via irrvcrtersNl anei N2 anci

its output goes

high, As a re-

sult, the outptttof timer: IC2goes high. Re-

R2>'"1-L

R5470O

LEDl

D11 N,100 i'

gf..*^/fw*--R51K

lC1 (N1-N4)= CD4049

Fi!1, 2: Sensor installation in lhe overheadtank (OHT)

RL1=12V, 1C/O HELAYM:WATEB PUMP MOTOR

lh 3

r-{Mto-TI4 n.r

B rcitt1

Fig. t: Sinple ,vale( levei controllcr

L'rril, irlotlnd tirner NE555 and

in\".:r.tr'r brrficr CMOS lC CD4049'

Il usr.rs reaciil),-;rvailable, low-costcornpolrr-'nts, and is easy to build:ind install orl the over-headtank (Ol-lT') to prevent wastage of

ivatet.'l'hr: circtrit rvorks off a 12V bat-

terv or 230V AC nrains tlsing a 12V

aclaptor. I he three sensors builtfrom nott-corrosivc rnetal are fitted

to tire OHT as shown in Fig. 2 anci

come'ctecl to the circuit (Irig. 1) at a1:-

nrr>oriate terrninals. Power supply ter-

; ,,,t :,..',:.,\\tt\it:31:1r'a;:t/:ir,1&:t-r,.;ikitF,l;Wizt:itiAiji&f;1:'41";t*i4ifittt;*witxifllt;jliii\i,#isttild:s;EwLt.ii}'riewi''dd#.lv'w*m:iw;iew9lit :itd#i:b"''"tte:*; ndait::drtl

WtJ!'V,EFy11lA1i.COtui ELECTRONICS FOR YOU SEUiiUAitY 2007'91

2-4>4e-

do-it-yourself

'1 hc lvlag,ic Eye is a versatile electronic eye that can

i.rc usetl for a variety of applications like a burglar alarm,snrokc cietector or an autornatic guest indicator. All these.

applications make use of the Light Dependent Resistor(l,Dll), but installecl and irnplemented differently. ..

Musical DoorbellWith MemoryOVERVIEW

1

T--to-on

itch

n trupru I

lc1Melody

Generator

rransirtor) |

rz tnpru I

Qutput

Iranrirtorf f-Pulh'to.

I Sr,vitch

ilnput)

Ilcl'orrr starting, check for the cornponents supplied witlrtlrtr kit against tire list of parts.

Stttilt:riirtfii[ai::;: ' ''.

l( I- NE555 \lulti-vibrator'/Tirncr

Fig. 1: Block Diagram of the Magic Eye

PARTS LIST

/icr.slslorr^ (trtl th-tuntt, *50/o carbon, wiless stated othet-il i sr);

l{1- 2.2 kilo-ohrnIi2- 100 kilo-ohml,iglit Dependent I{esistor

(r r)R)

C lltttcilors:C1- ?21rF, 12V Electrolyte

C2- 0.02prlt, Ceriunic DiskC3- 0. I U F, Cclaur ic Disk

Fig. 2: Pin-Out of a NE555Timer lC

L,liscellotrco us:

l.S- 4 ohnr, 1W.ltt LoudspeakerPrinted Cilcuit lloard (PCB)

COMPONENT DESCRIPTION

Sirr,glc 7 ittu'r lC Nf555;'lhe N8555 timer IC is widely-usecl in circuits requir-'

rrrg precisi-. tirrn cle.ln1,s or oscillations (pulses). The NE555

Lr:;rr,rlly' lrpr.atcs irr tu'o ruocles: mono-stahle nrorie (for

pLoducinll a single pnlse rvhen triggered) and the astable

nrod,c (for gcnclating pulses ol oscillat'ions with thc desircd

duty rycle).'Itre threshold (Pin6) and trigger (Ph2) level lrrrthe NFl555 are norniallv two-tllirds and one-thircl, respec-

tively, of thc comnron-collector voltag,e (VCC). I-Io'.ve..'e..,

Fig,3: Reprcsgntation and Circuil Synbol of an LDn

connecting the trigger ilput to the tlrreshold input causes

the NE555 to run as a rnulLlvibrator. Tlris is kuorvrr as the

astable rnocll of operation whereby pulses or: oscillationsare generate,l, the frequenry and duty cyclc of which can be

conholled inr{ependentlv with tvvo external resistors arrd .r

single external capacitor (this purpose is sen,ect by I(1, ll2,tl',e LDR'arcl C3 in the'Magic Eye circuit).

The res'et ph of NE555 is 'activelow', i.e., when tl're voltage on this pir.r

falls below 0.7V (approximately) itmakes the output low too (0V), overriding all tlre other inputs. ln the MagicEye circuit, this pin is norurally held

high in the astable rnode, the output(Pin3) of the NE555 becomes high and

oscillations are gerreratecl at this pinwhich can be used to drive loudspeakers, motors, piezo-

elechic transtlucers, etc. The ortput of this IC can sink and

source rlp to 200mA, This is more than most ICs and it issuf{icient to supply many output trans-

ducers directly, including loudspeakers

(with a capacitol in series to block the

DC and allow the AC to pass).

Ligitt DeperuIeni Resistor (LDR):

A light dependent resistor (LDR) or a

photo-resistor is a resistor whose resist-

ance decreases with increasing incidentlight interrsity. It can also be referrecl to

as a photoconductor, An LDR is made ofa high resistance serniconcluctor. If light

falling on tlte device is of high enough lretluency, photons

c0l\.4I

Flg.4: SPDT TollgteSwitch Notations

@ Kits'n'Spares

absorbecl by tl're sen"ticondgctor gives it enortgh energy to

,'ontluc( electricity, theretry lowering the resistance' Tllis

teatru t' of I'hc LDR is srnartly combined ilr the circuit to ac-

tivatc or de-active the alarm generated through the NE555

tiurcl if-.

It csis t ors;

Ohlr's Law (Voltage = Current x Resistatrce' i'e'' V =

I r R) gou.r., th" *o1kitlg and application of resistors'

'l hat is, their basic role is to limit the curreirt or divide

tho voltage lvithir. a circuit' More often t!'ran not' ttre

.ornpone;ts in a circuit have different voltage and current

r:ori,-rf,r, hence the use of resistots hecotnes indispensable

anLl conttnon.

Caltacitors:

Capacitors store electrical errergy in the form of elec-

WORKING PRINCIPLE

tlic charge, 'fhey are used with resistors in timing circuits

bccause lt tokn" time for a caPacitor to fill with charge' In

thc lv{agic E)'e circuit, the values of resistors R1' R2 and ca-

pacitor"C3 tlecide the frequencv of astable oscillations being

llerteratctl by the NE555 timer IC'

No'te: Iilectlolvtic capacitors are polarised and must be

contrtlcted irr tlre correct \^/ay' otl the otlrer lrand, cerarnic

capar:itors clo not have polarity-specific connecfions and can

be cortnectecl any way aroulld'

'l'tre Magic Eye circuit eirlpio'iis a si:::plt ::rec!-:o-nis$

kr souucl ati alarur when a shaclow falls on the LDR' In

the r:ircLrit, the Light Depenclent Resistor (LDR) varies its-

lesisttruce corresponcling to a variation in the intensity of

tigtrt falling o,', it. fypicaUy, when the light intensity is high

tlicy offer u t iglr r.rirtuttce. However, *h:n 1shadow

falls

u,, ih. t,DR (i.e. the anount of incident light decreases)' the

lcsistattce of the LDR rapidly falts'

Corrsid* two cases: J

l. In the abserrce of any guest or intmder' tight is di-

rectly incic{ent on the LDR and its resistance is high' Since

the NE555 timer IC is connectecl to operats in the astable

mocie bf operatiotl, this high resistance offered by the LDR

ASSEMBLING TEE-{!I

generates an inarrdible outprtt at Pin3'

2. Colversely, when the sha<low of a guest or an in-

tLucler is cast upon the LDR its resistance decreases' This'

change in the re^sistance of the LDR correspondingly alters

tt',. ,t.tty cycle of ihe osciiiations generated at the output

pin (l'in3) of the NE555' Tlre frequency of cscillations gen-

elateci is now in the auclible range ancl this is fed to the

louclspeaker thr:ough the capacitor C1' The loudspeaker is

basicalli' a transclucer that converts this oscillating elechi-

cal slgnal itlto souncl vibrations' IIence, an alarm sonnd is

g",rerat.'ct bv the Ioudspeaker to alert about the guest or

intruder at tlte door,

Com pononl I dentilication

T^pt"f"iir"r"uype after Assembling the Components and Soldering

do-it-you

Prcpaing tlrc soldering iron:

PlacJthe soldering iron in its holder' Plug it into the

AC socket and switch on Power supply' Typically' the iron

takes 3-5 minutes to reach its operating temperature (ap-

prox,400"c).You can check whether tlte iron has reached its operat-

ing temperature by trying to melt a little sqlder on its tip'"Before pro."".iing, clean the tip of the iron by wiping it

with a damPsPonge.

S olrlerin g tl rc cor trP ou et ft s:

. Use the conrponent overlay on the lrCit to in'sert iire

components. Solcler them in the following ol'der:

1. Resistors

2. CaPacitors

3. IC socket

4. Light DePendent Resistor (LDR)

5. Loudspeaker

6. Connection to SuPPIY

@ Kits'n'Spare$

t--io-it-Yourself

I loict tlrc soldering iron near the

basc of its insulate<l handle' Make

su r'e' thal your hand does not tcuch'the metal.lic tip at any point of tirne'

Position the soldering iron in such

a rranner that the tip n-rakes contact

r,r,ith the ioint to be rnade' Ensure

that tt tout:hes the conlponent lead

trs well as the track on the PCB

Once the joint has heated up, feed

sonre sokler arnd allow it to flort'

orto the lead and the track to forrn

.r r,olcatto shaPe.

()nce tlre joint has been soldered'

r-.rle[uliv Lenlove the solder bit and

thctr the iron, rvithout disturbing

{o soldering. (1ihe sockets atld not tlre ICs are soldered

on the PCB, this is to rnake the rnounting

ancl dismounting of the lCs easy while

testing and troubleshooting). "

IC holders and socketq should

be soldered with the notch at the correct

end.. Note that the LDR does uot

have polarity specific connections' just

like anY other resistor

PBE.TEST

Do not insert the i'iE5'55 IC into the

socket yet. First, check the 6V '".tower

supply that is to be applied and its po-

laritv with a multi-nreter' Next' contlect

$is;6V direct current (DC) supply and

measure the voltage across PinS (+V cc),ii-,tlrt lex lr -formed joint'

After a1l the conponents have been soldered' closely'

t"rp..* the solderecl joi-nts under a bright light' The

i,,i',ts shoultl look'shin1" and sltould be free from any

f r:.^r.r. Conrrectrv ity betlveeu closely-placed adjacent

pads should be checked with a nrulti-meter' in case

'ihcr,' is an ulrwatrted solder briclge'

Precutrtiorrs to be takut:. It is preferable to use mulhi-thread wires rather than

single tlrread copper wires for external connections to

thi,iloudspeaker, silce the latter tend to break upon*aolcie-Ling..-

. 'fhc pillJnf tt.te IC sockets rnay have to beadjusted and

l:ent tn oleler to inset:t thern into the drill holes prior

ancl Pinl (GND) of the N8555' It should read approxinately

ZV. ff ,i it readi-ng is okay then remove power and insert

it',. tC lr-rro its so&et. Take care not to bend any of the IC

pat *ittf. tloing so. Accidentally applying a voltage larger

'ttran tO votts to t-he cilcuit can buln the IC or other sensitive

cornpollents in the circuit'

TESTING

Now, apply the supply voltage to the circ'uit' 'lhere

should be no alarrn sound'in the normal staie' To test the

*"*"g of the Magic Eye, cover the LDR with 1'oul'hand or

with an oPilque pen-cqp so as to shadow it from the light in-

ciclent onlt, As tlie obstruction biociis ihe iigir'L faili-g on'J'.e

ilii it" the anount of incident light clecleases)' the rcsist-

url.u of the LDR rapidly falls and the NE555 Senerates os-

+c2470p12V

--- -_'-_-1 iillations of audible frequency'

Hence, an alarm sound will be

generatecl bY the loudsPeaker'

LSYOI

TROUBLESHOOTING

T3

If the circuit does trot work

as desired then the Procedure

clescribe<l below should be fol-

lowed:. 'It is preferable to begitt

the troubleshooting Process

front the outPut stage or'wards

and then Proceed to the inPut

side. to begin, check for volt-

age change at Pin3 (outPut Pin)

oi the NE555. When the LDII

is not shadowed, the voltage

level of this Pin shoukl be 'lold'

I-lowever whcn tlte LDR is cov'

ered with an oPaqtte Pen-coP or

by hancl, the voltage at this pitt

sioul,l go fr'orn 'low' to'higlf

'I B7(or 8C547)

T186548

Fig|. 6: Cucuit Dta(ltL\n of the Musicat Doohell with Memory

O Kits'n'Spares

do-it-Yourselr .

ouifed value' Make sure that you have the right conr

ionents in the right Places'

dn." ,f't" circuit froblenls, if arw' have been resolved

yo.rr Mugi" Eye is ready to'be:installed and used!

(approximately.r.l2$' If this kincl of switching action

iriuLirlg place then your IC is working else ther:e may

trc probiem in the IC' -

Remove the IC from the lC socket and check that no

ii'i''t* ";" o"nt up uncler the bocly of the IC' T:t: ::l.

sometimes happen while inserting ICs ilto so9]<!ts;r

Checkforvoltagesatcharacteristicsocketpins.Typic4l.values can be checkeci for by:referring the datasheets' If

ti',L tC opp"ut, to have'heated'thgn replace it'

. itl".t rtre polarity of the eleqtrolytic caPacftor

iri*'rft", all'thd resistances:beirig used a*'e'1of the re'

CONTACT DETAILS

f,f;lort pfete catalogue of'ewailable kits' visit our web-

site: www.kitnsPares'com

Doownented bY Aditi Gosvrani

.-,tl

CF'-

:

:jr t::

o Kits'n'Spares

^rL5 n >paresl-SS.5. O<..- I::_si: = ;-=aPhaSe-I, [Jey., Deirr_1iO02CPhone: 2637166I, 26371 662e-nta;l; ft.il 59 efl rnd.a.comwebsjte: wrvw.k,tsnslJEr...,,,

VARIABLE POWER SUPPTY WITIHf,}E6lTA!. C0$,!TR0tMAruESH T. MATHEW il'e1l as negatit,e DC output. LEDI, alcng

\yith curuent-limiting resisror Rl, is usecifor ntains'on' indicarion.

l.rboi'.:tories is a univer.sal porver-Tirner lC NE555 (lCll js wireci as

an astable rnultivibrator. It generntesclock pLrlses rvhett srvttclr Sl i: .ro. .l') lrc oirrprrr oi tC I is .ou,r.i,.,ri'r," ."RC netrvork, to the clock input ofcornfer iC CD1O17 (iCJJ

tL LUqu L t; .r de,..]jc ;ir:g courttcr.

he nrLtsl frequently used devicerir elccrronic workshops ancl

:.lpliv iirat ltrovides .l variable, flrrclua-iiirr iti.,f {-)ilt;ritl. llete u,rt Ilresent a v.tri_.:irl:' l)r)r\'..f sLrpply rvith djgital coutroli|;'t. sintirl.';ritd e.ts,,, lo construct.

the output-setting vaLiable resistors(VRset, VR1 rhrough r.'R9), giving arrourput vnltage al pin 2 of IC4 as follirvs:

Vur, = 1.25(l + VRset/R16).Presets \/Ri rhroLrgh VIig are ad_

justed tc 6et ih: c.-s;;:: oijiDiji,,._:lia6i.The coliector of transistor T1 is direcilvconnected to ADJ terniinal (pin t) ofIC4, so the 0utput voltage of IC4 willbe the voltage across fixed resistor.Rl6,

J 0 t-04 = 1t&007

VR1,VB! : 4.7K FBESEf

\:]

.

X1 = 220VA(] PFlIIARYTO I 2V,0.1 2V

J A SECONDARYTnANSFOU[1En

ltf,a.t sti..tK

47o

C52?00r

rerrs lTl-.] --2, :l(

rriOM

li ,.,.] 0 tlr

,12V DC

C;ND

r i.5V lO12V DC

VARIABLE

OUTPUTS

IIEAT S[.]K

I ==-

cl01p

25V

S3PT]SH,I O,ON

swlt r-'H

I

reos FTVI -{-4Rs14

LED3.LEO11 : GRE€NT1.T10: 8C546R7-R15 = IK

lbii: .l .lerntinri positive-voltage regula-ior IC t.\4317, L-MOS dcc.ide counter. ICr-l) lr'l l. iilrt{- rf' \.!555 .rr:i1 3-telll:;lllliir ed ;r,:i;a I i,,'e-\'ol tagrl regLr la tor LM7 9 I 2.'l'ht'it(l nlalt)s supply is steppeciiirn,rr lr),rr.arrsfor.rner.Xl to deliver a\,',, il,l.rr\' ,rr,tl'ltt 0l IZV U-12V AC, lA.'i'irc ctirtltrrr 0i llre lranslorrntr iS recti-iitrl bi, .i irll-rvavr. rL.ctiiier rrotnprisingrli0riEs Dl titroLtgh l),i. Capacirors Cithrorii;it C4 ale cilrnr clecl in para)lel torL.dtil.ier diotics,., bvpass undesired.g il:, ., ,trr,l Lrr r rviill' s;l)rr0tlt .iriJ fittctualioi,-1rrr: porvt'r, Cap.tcitors C5 and Cl3.ric Ltseil ,rs iillers to ciitninate r.ipple.iile both ncgati\/e ancl positive lra)frvcifs itlrr itscrl to oltiairr posilive. as

Each of its ten outputs goes high one byonewhen a clock pu)se is received. TheuuLtruis cri it. rij4Ul/ afe COniteCied t..,

the bases of transisiors Tl through T'lC,respectively, as shown iI.I the figrr;.e. LED.)through LED11 are used here to inclicatcilre voltage levels. The collectors of tran.sistors T2 through T10 are connected t0p|esets VR1 through VR9, respectively,'"vhich are used t0 set the oritpnt voltage.

Adjustable vollage regulator ICLM3l7 (lC.l) rlevelops I .25V noruin.rlreference voltage (\, ,.) bclrvccn its out.put and the adjustable ternrirr.rl..flterefeience v0ltJge appcnrs across resistolRl6. Wlterr thc' voltagi: is constant, ac0nsIant cr]rlent florvs through one ol

rvhich is equal to 1.25V. Wher srvitch53 is pressed, pin 3 of IC2 goes higlr,::r(j rlte ourpur volrage bccornls l.2Vl

When switch S2 is presseci., the out_put of ICI goes high. .A.s a result, theoutputs of IC2 go high onc. by one. as .-r

ring c0ul)ter. Sirrce prcsets VRI tlrrougirVR9 are corrnectcci at the collectors

"of

transistors T2 thrcugh Tl0,,,respecrively,different oulpr.lt resjsl.tnces appear be.tween the acljustir,,le .:nit ground termil, ,ln,ils of iC4, rr'siiirirrg in diiierent ourputVolt,1gs5. By rrs,:. ,r properly caljbrafeLldigital nuiritncler y(.;L] carr easily aajqptii;rl ,:tlre presr..rs to obt,ri.rr l.5V ro l2V.

A frxed, negarive l2V DC can beobtained b1' usitrg fi.xed, negative-volt-

aBe feililialor lC LM79I2 (lC3J. Thuslhe por,r'er suppl-v unit catr be used forr:ircuits reqLriring both negative and posi-

ii3!1 :,1;:i: tr 'i

tivrr DC voltages.

When CD4017 is reset by pressingswitch 53, the output voltage becomes

1.2V and all the volt.rge-indication LEDsturn off. LED2 is used to indicate thenegative l2V DC voltage.

DETAILED DESCRIPTION

Arrplication of the circuitA requlated power supply is one of themost important and essential require-rrrent in electronic lab. The availablepor'/er -r'-rpply must provide variableoutputs ir.r steps as different appliancesiequrre different supply voltages vary-ing in the range of 1.5V to 12V. Also,

the outputs must be easy to select andunit shoulci provide proper display. The

iti'es€ni circuii is r.iesignecl with keep-ing above points in mind. lt gives vari-able and fluctuation free DC voltage as

output in the rangr-' of 1.5V to 12V.

Proper display of output selected, nega-tive supply voltage and mains ON con-dition are provided using LEDs.

Explained working of circuitDividing the whole circuii in two parts

as power supply section and voltage se-

lector section, we have their detailedworking as explained below:l. POWER SUPPLY SECTION; Trans-

fornrer X1 steps down 230VA,C.mains to 12V-0-12V, I A A.C. current.Diodes D1 to D4 form a bridge recti-fier to rectify stepped down voltageiu D.C. wiriic adiid!;ioi5 ii to C4 uy.pass undesireil spikr:s. Further filter-ing is perfcrme.cl by capacitors C5

and C13. Tliis positive 12V DC outputis Lrsed to operate lC1,lC2, lC4 and toget variable output. A fixed negativel2V DC outilut is obtained using lC7912 (lC3). Yellow LED2 indicatesnegative 12V output while Red LEDIindicates mains ON condition.

.l VOL'IAGE SILECTOR SECTION: Thevoltage selecting section is used toobtain variable voltage in nirresteps, from 1.5V to 1 2V. The sectionis ccntered around variable regula-tr:r lC 1M317 (lCa). The versatility ofthis lC allows us to obtain voltageranging frorn 1.2V to 37V. But as in-put here is linrited to 12V, the lC out-put is also limited.fo this level. Thevoltage at its output pin 2 is relatedto input resistance as follows:

Vout = 1.25(1+'VRset/R16) Volts.......Eq. 1

it is c!ear fron'r al:ove equation thatto vary Vorrt, VRsct shuuld be varied(keeping R16 fixrcJ). |lert' Rl6 is set to220ohms and VRset i:l tire :iariable re-

sistance. A particular lireset should be

selected at a tirne srtch tlrat voltage var-ies accordirrgly, This is dontr by lC

CD4017 (lC2) that is configured here as

decacie ring counier. ;At each [lockpulse, the counter advances its otltput

to higher stage. The clock pulses aregenerated by astable multivibrator us-in-q lC NE555 (lC1) whenever switch 52is pressed. The output selected turns ON

the respective transistor (T1 to T10 tran-5istors acting here as switches) and pre-set connected at that transistor getsconnected to regulator. The output volt-agr: varies according to value of resis-

tance offered by this preset" The corre-sponding LED also glows to indicate se-letr.ed voitage levei-

For exarnple, when switch 52 is

prerssed eight times, decade counter(lC2) gives high level output only at itspin 9. This enables transistor T9 to con-du,:t and LED10 starts glowing.The pre-

set VRB is connected at collector of T9

and adjust pin 'l of regulator (lC4). Thusvoltage Vout is proportional to resi5-

tance offered by VRB (putting VRset =VR8 in Eq.1). As value of VR8 is already

set to provide 10.5V, the desired out-put is obtained.

, When reset switch 53 is pressed, firstoutput (pin 3), gets selected to turn Tlon ancl VRset becomes equal to zero.

eutting VRset = 0 in Eq. 1, we,have Vout

= 1.25V. Thus at reset, output voltagebeco.mes 1.25V. ln this way, the unit is

::rp;blc cf prcviding bcth negrti'.,e :nCpositiveOC voltages.

Sctting the outputs

The circuit will not provide proper volt-age outputs without prior settings. Onlyafter proper settings are done (de-scribed here), the circuit will give de-sired outputs without any hassle.

1. Cornplete assembling and solderingof all components on the PCB.

2. Connect transformer's primarywinding to 230V AC supply throughswitch S1 and fuse F1.

3. Connect transformer's secondarywinding to 3-pin SIP connector(SlP'l) orr PCB. Wl.rerr S1 is closed,LEDl will hght up to indicate mainsON positian. Yellow LED (LED2) will

I also turn ON to indicate negativel2VDC voltage.

4. The outputs are to be set using a

properly calibrated digital multim-eter. Select appropriate voltage po-

sition of multimeter and connect itscommon terminal to GND of the cir-

cuit. Measure fbttage at negativeoutput tenninal of circuit. lt must be

-l2V on its own as no setting are

required for this.5. To set variable voltages, connect

multimeter's positive terminal to

IC3lc4

LM7912LM3I7Transistor BC54BDiode 1N4007Red LEDYellow LED

T1-Tl0DI.D4LEDILED2LED3-LEDl1 - Green LED

Reslstors {all %-watt, L50lo carbon,unl ess stut ed othera i se ) :

Rl, R7-R15.

31/_ "_R2R3

R4, R5R6

Rl6VRIVR2.VR4VR5-VR7VR8, VR9

iti

Capacitors:

Cl-Cc - 47nF, ceramic .- q?3C5, Cl3 - 2200pF, 25V electrolyticC6 - 10pF, 25V electrolyticLl - U.U t pr, cerarnlcC8, C9, Cl2 - 0.lp!', cer,rnricC10 . lpF, 25V electrolyticCll - 0.22UF,ceramic

Miscellarteous: '

- lkilo-ohrn- 22kilo-ohm. 5btj-onrn- 8;2kilo-ohrn- l0kilo-ohn- 220-ohm- I00-ohrl- lkilo-ohrn- 2.2kilo-ohnr- 4.7kilo-oirnr

Lo 'otr V"lr f)

SI . ON/OFF switch52, S3 - PUS|I-TO-ON Switclr

^iri !.t^,1..--.--._-i rll i-C t'ir'r Jli' r tirriitlltii - -Transformer 230V to 12-0-12V,1AFuse lA (

Heat Sink (for lC3, IC4) - 2

PCB

7,

variable output terminal of the cir-cuit. Now, press switch 52. LED3 willglow to indicate selection of firstoutput.Vary the output voltage by rotatingthe preset VR1 position until it is set

to 1.5V DC.Again press switch 52 so that nextoutput is selected. LED4 will glowto indicate selection of second out-puf. Vary the output voltage by ro-tating the preset VR2 pcsition untilit is set to 3V DC.

ln similar fashion, oo on selectingdifferent outputs and set the out-puts accordingly.Note that these settings are re-quired only for the first iime.

10. Desired outplrt flovJ ortr,vards can be

oblained sirn;.;iy hv selecting it us-

ing switch 52 arrd riren connectingthe 'load' acro:s output t6rminals.For example, to select 9V output,press 52 seven times.

Noter Switch 51 and'F1 are not on PCB

but connected separately betweei,transformer and AC mains.

I

I

___l

6.

8.

o

){

KS Project Manual

Heat Sensitive Switch(EFY Nov. '0S;

Description

'iht circtiit prescnteci here catt be usecl to turn on (or off) t,re loacl coriiicctcC gcrcss therelay at a predetermined temperature. At the heart of this i.e,at-sensitive switch is ICLM35 (IC1), which is a linear temperature sensor and linear temperature-tb,voltageconverter,circuit.

ing input (pin 3) of thecomparalor IC2, The inverting input (pin 2) of IC2 is connectJd ac.oss the p*itiu.supply rails via a voltage divider network fonned by potmeter VRl, Th;;;tde at pin2is used as the ref'erence level for the conparutpt uguinrt the output ruppiirO tViCr

So if pin3 of fCz-receives a voltage lower than the set levcl, its output goes lour

(approximately 650 mv). This low level is applied to the input of tire lJad-relay drivercornprising npn transistors T1 and,T2 and tliey are in cut-ofi, Hence, relay RLi is in de-energised state, keeping mains supply to the load 'off as long as the temperatur.e at thesensor is low. Conversely, if pin3 input receives a voltage higher than the set level, itsottti;tit goes higi. (apprcrxinratlly ?200 "1\./) und tlir; ioaciis i;;ii,,.i ,uri.' iiris irappenswhen IC I is at a higher temperature and its output voltage is also higher thu" trrr set levelat pin2 cf IC2,

Assembling ancl Testing1' Clean off any dust and dirt front the PCB with paper torvel soaked i1 thinner/acetone(nail poli sh renrover).2, Trace the conductor lines ancl com;nnent markings on [,cB and rnount eachcomponent conectly.3' Check.coffect polarity o1 the power supply before conne ctiirs power to the circuit.4'Yary the reference-voltage level potmeter VRI at the invertinj input pin of iCt to ,rtthe temperature threshold at which Lnergisation ortne rJ]'ir;;"q;til.'N;;; tt ut tt .knob of potmeter VRI can be provided with a linear dial calibrateo in degrees.r"iigrrO..Hints: Suppose, you want to switch on the load at 50oC. ,Heat the .rnr6, with solderingiron until 50mV is obtained at pin2of the serisor. Simultarreo;rt, til;u, to'uary vntsuclr that pin6 of CA3l30,becomes'"high. This will enable tu.nlijire tir. rriuy and tumon the load. Keep the setting of VRI at this position for futurc ur.] ro ttrat wnlneverthetemperature reaches 50oC , the circuit rvill autornatically sr.r,itch on the load. ;

Parts Listl!"'

SemiconductorsIClICzrc3T1

T2Dl- D5I-ED1, LtrDz

CapacitorC1

C2

C3

C4

Miscellaneous

X1

RLl

- LM35 temperature sellsor- CA3130 Comparator- 7806 DC voltage regttlator- 8C549 NPN trartsistor- BD139 NPN transistor- 1N4007 recti{ie"' diode- Smm light emitting diode

Resistors (all t/t-watt, *5o/o carbon)R1 1.2 kilo-ohmR2 - l0 kilo-ohmR3 - 12 kilo-ohnR4 - 680 ohm

R5 - 15 kilo-ohrn

R6, R8, R9 - 1,5 kilo'ohmR7 1 kilo-ohmVRI - 10 kilo-ohrn log Pot

- 47vf, 10V electrolYtic- 1uf, 10V electrolYtic,- 0.1uf ceramic disc- 1000u1 35V electrol$ic

- 230V AC to 0-12V AC, 250mA secondary transformer

- 12V,200 ohm lC/o relay

. '.,

Description of main comPonent(s)

LM3S: The LM35 series are precision integrated-circuit temperature sensors, whose output

voltage is linearly proportional:to the Celsius (Centigrade) temperature. It develops an output

volta;e of l0 mV pft d"gt.r centigrade change in the ambient temperature. Therefoqe the output

,;;i6; varies from 0 mi at OoC to tv at 100"C and any voltage measurement circuit connected

urrori the output pins can reari the tenrperature directly. It can be used with srngle power

supplies, o, *ith pius and nrinu; supplies, As it draws only 60 nrA from its supply, it has very

iow seif-heating, iess than'O.loC in still air. The LM35 is rated to operate over a -55oC to

+150"C tempeiatrxerange,whiie theLM35Cisratedfora-40oCto+ilOoCrangel-lOoCu'ithimprovecl accuracY). r

cA3l30 : cA3130A and cA3130 are operational amplifiers that combine the advantage of both

cMos and bipolar transistors. The cA3130 Series circuits operate at supply voltages ranging

from 5V to l6V, (+2.5V to +8V). It has many applications which includes high-input-impedanceiomparators(IdealInterfacewithDigitalCMoS)-

iltffiRL1 I)* Iaol3s I

Circuit diagram of heat sensitive switch

7

Mffiffitcal'Toucht Be$lOVERVI[$/

iin-it yourself

N/l()st ( or1\'rlntiorral calling-bclls avililable irr the urarke t

t',rrr oulr, i)c r)lrcratcrl rvith a tnccharrical on/off switch. The

rrrrricnl frrLrr lr lrcll inrpleuretrted herc catr bc' operated Lly

irrsl lrrirllliriii tlrt: 11;rp l:rctweetr two touch-plates bv otre's firr-

T(rudl Plalq, -)

{f;(til! lil!iltl

t:ig. l. Block Touch Bell

gr:r'tiprs ani{ r'r:cluircs utinintal polver, T'he circuit generates

.r |11'11s'1111 rrrr;icill touc through a nrelody-generator itrte'

11r'alcrl crrr urt (i( ), ns loug as thr: tottclt plates are in contact.

PARTS tIST

_ $efore starting,ciltck il-,e CUirrpo'

' nents supplied with

the kit agaiust the

list of parts.

C()MPONENTDESCRIPTION

l.S'lt Ohnr, 2 lVatl L,outlsgre;rker

S( t ('lvs

l'r'irtlecl ( il'rrrl Il',rnl (PCB)'1: Generstor 13T66'I'

" : ktr llM66):

'Ihe 8T66T IC

scrics is tlt'si1';uccl fol usc' irr doorbells, telephones arrd toys.

I lrc t:lrip r1i'rrL'r.atcs a nrelorlior.ts tune at its output pin (Pin1)

n'hirn porvi'r' is appliccl betweeu its Pin2 and Pin3, Sonte of

thc rrrarr\, {carult:s of the 8T66T inclucler. 64-notr, r'i'atl-onl1, ulemory. l.tltr, r,r()\'\,L't LoitsutrrLrtiou. l-)r,uanrit speakcr tlrat can be driven by an extenral NPN

trarrsistirr (lilic the !JEL187 /8C547), Orr-chr1, rcsistor-capacitor (ltC) oscillator. I'tr\\'cl on lcse t; melody begins from the first note

'lirt' nrrirrtil, gerreratcc'l by the chip depends upon the

l'rirlt rlrnrlrL'r' bcing usccl fronr atlongst the 8T66T family,

lrrrllorvirrll is llrt' Irst of available sottgs:

l] l'()() I, ii)l ,; lroI lllisc

ll 1 66 I - il 'l : lingle llclllll66l' ilill.: I lappv llirthdayl] I6() I- I"ll ,: Love Storv

ICI'il'1'2

'l i

-li't'6(r (rr UM66). i 'i,', i r aniistriir DC54t3 ,i- 1'r'arrsislot RC558 '.''- {'rarrsisttll BEl;i87 ,,

ftrL IlC5:tZ) . ,,

/(r si:1,,r: !1, , -;:'rll, t.\"/' cntlttin, ilttltss

;ltIitl ollt, ,,t t', t:lil ^l 2 nlrnt

A li.ri'/iiir', ,

t'l it'rPll!l0ri

5r'//llc{)lir///r l''' \

-

_---- --l

| #n''''''' Il'4'li: t" j tr1 ,t lll11",.r'1:,'o,l]lFig. 2: Pin-OLtt of the SimpleMektdy-Generi,lor BT66T

8T66T- 68L: lt's a Snrall

WorldThe following circuit carr

be ernployed for driving a

loudspeaker through the

output pin oI iirc BTooT arrri

an NPN transistor:

Fig. 3: Circuil Diagram lor Dridng a Loudspeaker ihrough the 8T66T

Output Pin

ln the above circuit, the rnelody is generated for as long

as the switch is closed.

'l ra; r i s tor s (;Y,l)l'J Ti;;, :- B €547/tsE!-787, IJC548,;;i C ;"lJ,l'

Type-8C558):

8C558 and BC54B are gtlneral-purpose lransistors used

for switchrng ancl amplification purposes. In the musical

touch bell circuit, these two transistors are basically oper-

ated in the following flvo modes:. Saturation (or conduction) mode: A bansistol is said to be

operating in the conduction mode when both ib junctions

are forward-biased. In this state, the haruistor facilitates

high current conduction from the emitter to the collector

and corresponds to a logical "ON" or a closed switch'

1r Cut-off: In cut-off mode, the biasing condition of the harr-

sistor is exactly opposite thart in the saturation mode, r.e.,

!oth its junctions are reversed-biased, Currelrt conduchon

is very low and this state corresponds to

a logical "OFF" or an open switch.

Or,r the other hand, transistol T3

(which can be either a BEL187 or a

8C547) arnplifies the varyirrg electrical

signal generated at tire output pin of

tsT66T. The amplified signalis available

at tlre collector pin of BEL787lBC547,

which is input to the loudspeaker for

turre gerreratiot-t.

Resisfors: .

Ohrn's Law (Voltage = Curent x Re-

I x Il) govems the workurg and application

Fig. 4: PinCon{iguralion ofTransistors 8C547,BC54B and 8C558

/i -t'.//(^;/\it--/ i

r -----,, /\rl /1 n \ilt'lMl''

tl[/tl // //

cut(-BE

sistauce, i.e., V =

@ Kits'n Spares

ffiJ,l ri'\r5Lt)rs. l'hat is, their basic role is tct lirlrit the cLtl'rent or

1r'.'tLlt'tlrl voltallc r'r'ithnr i ctrcltit N'lot'e often thalr rrot' the

l,',',,,,,,,,,',,,, rn a L irt:uit havc' differelrrt voltage and current

r,rt1u!ls; lictlcr: tlrc trse of resistors beconres irrdispensable

,\rlii r()lllll\l)ll

-------\t thc lreart of the nrttsical touch bell lies *,::il1l"

.i,n('I1 rtor l(- ll'l'66l" -l he circuit enlPioi's two transistors for

:.j,]]i, .'r"r'-',)tt"'u, *..,".n ;rtrcl iot'switching ou the 'relocly-

i,,t'rtt't'.tttlr 1(..

i\s showll irr the crrcuit cliagt'all' ti le ernitter of h ansistor

f r tflC::+Sl is shortecl to the groirncl while that,of lrarrs::::l:

ii,Hil.""'*.*' to the positive tcnninalof th:^'ll"o"tl; \ ,r,"r,..

,\iso tl',r colleckrl of trarrsistorTl is connected to o't: out:,:: I ::-:"",')ll,jl[i,]' ;,;;;;.';;;''";; conuectecl P 'r*

*,'::'jJX I component tdentiricauon

,,trilt:ctor of lJcl55tj is cotrnectecl to Pin2 of nlusical,lC::T: \ ,r"t*"ot*;*,# i.

r,ii,,'. '''"0

of ll'1661 rs shortecl to the ground' The output

tr..r,,r i'lnt is conrrectecl to a transistor amplifier conrprising

ii.i,' ,,',',lti7 transistor for feecling the louclspeaker' One encl

,,,,' l.],,t.tn', rtrsistor (l{1) is connlctecl to the posihve rail and

lirt,othcr to a screrv (as shown in *rc figure)' The cornplete

r ilr rril is corrlrtrctt:c'l to a single pencil cell of 1'5 Volts'

iht: trncicrlving meclianism is very sinrple' When

tlie touc[r'platt' '13up i' brictgecl with a finger' the enritter-

L rrllLrctoi' tLrnction nf t'ansisior "l''l starts conducting' Con-

r;r:r1 ue tr tlt', the e rlitter-base junctton :: jt:]]", :::"-:, :;;1::'rjtlLrstrrl-r ""lt

of this' the collectdr of 12 isstn|tl; aolrcltlctirrll As a rr

,.,'llr',1 rowitt'(ls the positive rail' lvhich thus activates thet"""''l,,..liu.''u-i,,,,,,.,'atrrr lCl (8T66l) to produce.musical tunes

,,,',',. ..',,,ir*, pirr in the fonn iil a varying electrical signal'

ll h, trarrsistol Btit 187 (or llc547) receives ures; v11]atiol1

i,lcctrical Variatious into auclible sotlnd, thereby gelleratillg j ^ . ,

rirL' rncloclions trtttsical tone' So, we hear a music;l1.ote iust \ :''f:1rr{.1:::ili::fltl

,,r(,\\ lrca(l l'hcwashcrco"i'tb'ui:.|,:']:i:,,1;:'"t1,",:].:l I it. ;'ffi;L."eratorlC,i:i'r',,.,r''"tn.:sive, while the.screw tt: b::::tll,il]:li:t \ i, ;'-..,til;' ,

,'';'li',,.;;;r;;'... useci for urouuti'g the touchdate I :' rrarrtsrrrurr

.^,.u^.r r^" I 4. Touch Plates

i lrt' Lrsc of ii brass washer at''cl screw is recotrrtneuded for | 4' I'(' i 5. LotrclsPeaker

AssEMBLINGIIE-[!T:

It'rttt't'rnttitc rrY t'r';' rr1' to melt a ":::,::1i::l:llti,ll." t, 1 ",*,* rn^P.

rvilh a danrP spolrlle o Kits'n'Spares

do it-Yoursei{ t:'l:.i

i\rl.d..

; i;,i:i::!,:li,

:ir

'ta

LoudsPoakol

;,,:

:.'l))i?t.i::11

li:,i,;::::::lli:lf,l'ffiliH:H:ffiilil^,: \ #t*,'dpro'|o'!vpeat'|erAssant)tinstheco'rnponen'|sand

tlr,,, l,,ur"trp,,uke r,'lhe louclspeaker converts tn:t-1Tfl::: I

il.:llffi1li'lllil.,irxl'l;:iil,'lTl[ii.''l:x:,1,'^":H; \ :"'ffi .on,po,,ent overlav on trre pcB to i*sert trre

r,h.Lrrd bt: I to 2 millinrei"' O"l greater '1"" liili* \ ;;ru*:;sotaer

thetl' iu the followir"rg order:

\ ' ii"ti tr"'tiiJt"ng iton near the base oitT l.t::5::hanclle. Make sure tlut your hand does rrot torrch the

metallic tip at any point of time' -.- rr-^r +r.o

i'"iil::'i,ii::'rlffiill'lnitstrorcrerPlugl"':':'l:f \' i:**i};1'XT}il':i'.'lffl';"#ilil:'tl.l*:ililix;Tliilf ;l?;i;:l*iT#tif"--,1* \ ll[l**;:lliliJX]*;l;il:J:n:',i'*';':T::iittltrtirlitls3-5tititrutestoreac}ritsoperatirrgtenPeraturellllatl[tuuLltlo!lrv!Y...r--'-1 on dre PCB'(aPl'rox 40i)'C)

il,',,i.,,,,,i,.",,l,irethcr.the iron has reached its opcrating ! ' Yt]* lit: luu* rrsJ

rih I allow ,, tJ fto* onto tl'rc lead arrti thc track to form a

,,.,,',1," p,nr.u,."ting,, .i"n'', the tip of the iron by wipins tt \ . ;il:'il';tii has been solderecl, carefully rer'ove the |fd

{ iil").\trt'!

[1{i

q

,ct ii-5rgt-.1rSelf

'olilt.r hit and then the irotr, withoutr I r r; I Lr rl.r r rr11 tlrc nelvlv-fornrdd joiut.

. .\ltirl all thc componettts havelrccn solclclercl, close lv inspect thesoltit'r't'tl joirrts urrdcr a blight light.i lrr' loinls slroulcl look 'shiny' ar-rd

slr,rrrlc{ [rt'frt'e from any breaks.( rrrrrrectivrty betweetr closely-

i,lirt t'tl acl,accrtt pac'ls slroulcl be

L irli'kcd ll,ith a tlulti-meter, in case

- . rlr, r, r'. un ,UlrU{d$I$+koltlcr bridge

l'rectulitttts ttt be tnken:. Note that connections to the loudspeaker need to

bc rnade externally using multi-thread wires. Pleafe

rclt'r to the above illustration to understaud these con-

n('ctions.

" 'lirt' thrce-lcggecl tratrsistor should also be carefully

placi:rl rnkr tlrc correct clrill-holes orr tl're PCB.

. ,\lso note that the urelody-generator IC has a packing

sinrrlal to tlte transistors 8C548,8C558 and BC547. Read

' tlrc part nunrber carefully before soldering the cotrrpo-

rrcnts inkr their respective drill-holes on the PCB.

. Ialic clre not to apply ltlore thall 3 V to the circuit. A

loltalic 0f nrore than 3.3 V nray damage thb ntelody-

ilute rat()r lC oI other sensilive comPonellb jn the circuit,

-+=+lffi ****?-

Fig. 5: Circuil Diagram ot the Musical Touch Bell

( hcck the supply voltage (approxin'rately 3 V) and

l)()lirlitv ol the DC supply (batteries) with a nrulti-meter.

'\ ppll thc DC supply voltage of 3 V by inserfing two AAA

irattlries rnkr thc battery holder.

TESTING:

' lo tcst the working of the urusical toucl'r bell, make

r on[lt I br'trve'crr the two touclr plates using your fingers;

tlrjs sltourlcl gelrelate a musical tune for a certail't time

i n tcrva l,

. I hc musical lLrrrc shoulcl be generated for as hng as the

platcs toudh (]ach other.

Tfi()UBLESH()()TING:

l1 tlrc citcLtit clocs ttot work as desired, the procec'lure

iir,sL rilrctl below sltoulel be foliowed:

to the input sid,r. To check the alarm generationmechanisrn; apply f irigh' {a.pprox. 3 V) to Pin2 of the

nrelody-generator IC. This will cause oscillations to be

produced at the output Pinl and generate a nrusical

tulte at the loudspeaker end through transistor am-

plifier T3. If this mechanism is working as described,

then tlre circuit stages beyond IC1 are OK, If not,

proceed with the next step,

Check the cor-\uectiou of components like the transistor

and the melody-generator IC. Also check that the resist'

ance being used is of the required value. Make sure that

you have the right componens in the right places,

Check for voltages at the Vss and Vdd pins of the melo'

dy-generator IC.'I'he voltage belween these trvo points

should not be nore than 3 V. If the IC appears to have

heated, replace it.. Check for the voltage change at the output pin of the IC

when tlre plates ale tnade to touch each odler.

Once the circuit problems, it any, have been resolved

your musical touch bell is ready to be installed and used!

TRY THIS OUT NEXT!

The musical touch bell discussed here can be ir:lple'

nentecl as a calling bell by installing the loudspeaker at

the other end (where the person to be called is present)'

'Ihe circuit can further be extended to include nultiPle

melody-generator ICls (each with a different part nuntber

in the 8T66T family), each producing a distinct tune to call

a differeut personl

C(}NTACT DETAILS:

For a complete catalogue of available kits, visit our web

site: www.kitfi spare$,c0t'tl

Documenled by Adili Goswami!t is prt,lcrabte to begirr the troubleslrootinglr'()itr Ilr() oLrtput stilgL' ollwards and thetr

P IOCesS

proceed

(5rr-96qg'W

@HE soloenEou--porrur

./.]--T-a

@HWOODEN BASE

o(5'"'€rff"

m

O Kils'n'Spares

do-it-yourself

q

\!Li:i:e+T?ttapr'E';ltv.i:!rt$S4'e'S+t'&NS+d4t*A$EW_l'j&i!St'SW,,M14i#r14tvJ

r E I -il! ^ -I-r $imptc water Leuel lndicatorl:l OVERVIEW

The purpose of the water-level indicator- is to cau-

,i'i" tion a person when a water tank has been filled up to a

' .:1' narticular level. This circuit exploits the sin'rple fact that

rn'atcl is a gooci concluctor of elcctricify' The system is

:. '..: l..r .: l

Lll,llll;l:r:r1,ll

,,.11,11

, ,l i.:

I .,t.

Ftg. 1: Etock Diagram of the Simple Water'Level lnd[cator

capable of inclkating the water-level in two ways: vizual

lLry tt',ua,',, of a lighl-emitting cliode (LED)) and audible

iiry *.url, c,f a piezoelectric buzzer)' The placement of

t*o proU.,, 1witi, c,o,.nections to the circuit) inside the

watr:r tank cletermines the minimum detectable level

(NlDl-). Wlrerr the water reaches this height in the tank

io, u,.,y other lluicl container), the buzzer is activated and

the I,F.D is tirlned on.

iLevel lrrputi

':,.'.',,:,

j:ili:'

i: rll

PARTS LIST

llefore starting, check the cotnponents supplied with the

kit ag;ainst the list of Parts'Semiconductors:

T1- 8C107 transistor

T2- 8C547 transistor

D1- 1N4003

D2- Red Light Emit-

ting Diode (LED)' ::l)[-t{). 2: Aneltalion ol Diodes

llesistors (all 1/+'wntt, !50/0 carboit, rorless s;tatcd othenoisc):

R I- ,170 kilo-ohnr

li2- 220 ohrn

R3- 3.3 kilo-ohm

Cnpacitors:C1- 50pF (or 47pF), 16V electrolytic

Miscellaneous:Piezoelectric Buzzer

Prirrtecl Circuit Board (PCB)

ooMPoNENT DESCRIEMN

l)itrrlc 1N4003'lhe lN4()r.r3 is a semiconductor diode' Like any other

diocle, it cotr.ittcts electric current in only one direction

Fig.4: PinConfiguration of the8C547

while biocking current in the opposite

direction (known as the reverse direc-

tion). This unidirectional dehavior is

callecl rectification, and is used to con-

vert alternating current (AC) to direct

current (DC). In the water-level indica-

tor circuit, 1N4003 acts as a iraii-l-;ave

rectifier to rectify the AC voltage avail-

able at the secondary of the transformer

i" nC currer"lt. fhls is further filtered

lr), a capacitor. In its sirnplest fornr, a

half-wave rectifier can be in'rplerneuted

using a single diode as shoWn'

NPN Transis tars '8C547 and'.P,C1'07:

The 8C547 and the 8C107 are general-purPose tr3nsis-

tors used for svritching arrcl arnplification purposes' in the

water-level inclicator circuitry, these two transistors are

used as switches, i.e., they operate in the following two

modes:. saturation (or conduction) nrode: A trar-rsistor is said

to b" op"ruiing in the coucluction mode when both its

junctions are ioivyard-liasecl' In this state' the transis-

ior lacilitates high current conduction from the etnitter

to the collector and corresponcls to a logical "on" or a-

closed switch. Cut:off: ln cut-off mocle, the biasing condition of the

transistcr is exactly opposite that in the saturation mocle'

i,e., both its iunctions are reversed-biased' Current

conduction is very low and this state correspouds to a

logical " of( ot an open switch'

Tr-ansistorT2 (BC544 switches frorn "off"to "on" sbate

in orcler to generate a sound outPut through the piezor:lcc-

tricbuzzer,"while transistor T1 (BC107) srvitches in order to

provide visual indi-cation through the

red LED. This rvaY,

both visual and au-

dible indicltion of

the water'level isgenerated.

Single-Pole, Dort'ble:l'hrout (SPDT)

Toggle SutitcluAn SPDT toggle

switch nral' be used

as a simple on-off

sw'itch by cor:rnect-

ing the COM termi-

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ApoM

tslis. 5 Sf'DT Tuggie Sl,rilchNot;rrors

rr-rllent or clivicie the voltage within a circuit. More otten

than not, the componeuts in a cilcuit havt-- clifferent volt-alge ;rncl cllrrent rarings; hence the uset of resistors becontes

incl ispensab[e anci courtnon.

Ctyttrc itors:(.apacrtors store electrical energv in the fortl of elettric

chalgr:. Clapacitors are capable of snroothing varying DC

supplies b1' absorbing the peaks ancl filling in tl're valleys,

i.t'., they can be usec'l to eliminate 'ripple'. 'l'vpically, half-

rv"rve rt:ctifir'atior.r delivers ;r form of DC or.rtpr"rt but does not

produrc a (onstalrt-voltage DC. Iu order to produce steady

I)Cl {'r'onr a rc.ctifiecl AC supply, a t'eservoir or smoothing

capaci[or is placccl at the DC output of the reclifier. Iu the

w'aterlevel indicabr circuit, capacitor (ii sentes riris purpose.

Note: Electlolyfir: capacitors are polari$ed and must be

t'onrrectecl in tlre correct way', On the other haud, ceranric

i apacitors do not have polaritv-specific conner;tious and can

bc connecterl an\/ !va\/ arouncl.

WORKING PRINCIPLE

'ilrc water-level indicator ernploys a sirnple nlechanistlt

lti ciett'ct ancl inc{icate the water-level in a tank or any olher

t orrtairrer. 'l'he level-sensing is done by a pail olt Prol.res, the

rt'sisttrrrce betwet-'n which depends upon the water-level in

tlie [ank. 'l hese prlobes can be placecl itr l.wo ways ott the

rv.rlis ol tlrt' larrk or'\'ortlrirtcr:l. Both the protres can be placecl at. different points

on the warll lvirrg at the saure level/height flomtlre lrottom, This height detelmines the ntinintuntc1t'tectablt: water lr:r,el, or

2. 'l'he probes can be placec{ at clifferernt points lying at

tw'o clifft:rt'ut heiglrts from the tank bottorrr. In tl'tis

ciist, the probe which is placecl higher than the oth-

er cle l"er rm ines the rn ininruur cietectable wa ter-level.

\,Vhon thc water-level is irelow the mitriurutt cletectable

levrl (N'{Dl-), tlrere is inl'inite intpeciance between the two

1.11rbes, Ilcrnce, tt'ansistrlr '['2 remains in tht-' cut-off nrocie

()nrl clocs no[ ("olrr"[rct, i Iowever whelt water-level teaches

\ll)t. oL is abo'vc ii [he connt:r:tion betwecrr the probes gets

lonrplt:tecl (tlrror'1;1r tlte cortductirrg mecliunr of water) trnd

nal trrrcl ertht:r oi the othert.vvo termir-rarls (A or I)) to tl-recircuit. -['hc terrtrinatls A and

IJ arer irrterchalrgerable, andso the switches are usuallynot labc.llecl.

ITesistors:Ohn.r's Law (Voltage =

Current x Ilesr.slarrce, i.e., V: i x ii) govelirs the workingarrr{ application of resistors.

Thc-.ir basic role is to limit tl're

do-it-yourself

Cornpleled Protolype after Assembling tha Components at)d Soldering

tl-re base voltage of '['2 increases. T'his causes the base-entitter

iunction of '12 to get forward-biased and the piezoelectrir:

buzzer is tulned "on" to generate an alart.u sound. Thc

path from the entitter of T2 through to resistance I{3 is

responsible for forward-biasing the base of transistor Tl,'I'his switches'['l from cut-off to r:oncluction urode, thereb]'

dliving the re.cl LED to glow, FTence, whenever the wattrr'

reaclres the NIDI-, bolh the buzzer ancl LED inclicate thir;

sinrulLaneously.

ASSE$,IIBLING TTIE KIT

Prcyorittg tlrc soldarittg iron:. Place the soldering iron iu its holcler. Plug it into the A(l

socket alld stvitch on the Power srrpply. Typically, thtr

iron takes 3-5 minutes to reach its operating tentperaturt'

(approx. 400"C).

' You can check whe'ttrer the iron has teaclrerl its operating

tenrpelature try tryin6 to rnelt a little sol,lpt'0n its tiP,

. Bt'fore Plocrxrtling, clean thc tip of tlre ilott bt, wiping it.

witlr a <Janrpr sponge.

C ompo ne nt I de nt ificat i o n

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Fig. 6: Circuit Diagram of the Simple Water'Leval lndicator !|_

S o I rI e r ing the c o n P tt ne uts:. Use the con'rponent overlay on the PCB to insertl[re

cornponents. Solder thern in the following order:

1, Resistors

2. Capacitors

3. Transistor

4. Diode

5. PiezoelectricBuzzer. Holcl the solclering iron near the base of its insulated

hancile, lr'laktr sure that your hand does not touch the

metallic tip at anrr point of time.. Posilion the soldering iron in such a manner that thetip

makes contact with the joint to be made' Ensure that it

iouthe3'tfiii-tbnipArcnt ieail' dt-wblt eii'fne ftaek on ihe

PCB.. Once the joint has heated up, feed some solder and

allow it to flow onto the lead and the track to form a

volcano shape.. Once the joint has been soldered, carefully remove the

solcler bii ancl then the iron, without disturbing the

nen'ly-lbrnrecl joint,. After all the components have been soldered, closely

inspect the soldered joints under a bright light. The

joints should look'shiny' and should be free from any

Lreaks. Cprrnectivity between closely-placed adjacent

pacls should be checked with a multi-metel in case there

is an unwantecl solcler bridge.

Precsrttions to be takefl:

:) ,:::ti,i.t:ti I',:,'l ',.illii

It is preferable to use rnulti-thread wires rather than

single-thread copper wires for connection with the pi-

ezoelechic buzz.et, since the lattel tend to break upon

solclcring.

Note that the red wire from the piezoelectric buzzer is

comectecl to the supply end while the blue wire is con'

rrected to tl're negative or ground end.

. The three-legged transistor should be carefully placed

into the correct drill-holes on the PCB' When corulect-

ing the transistor BC1O7, ensure that the direction of

the notch marked on the PCB coincides with that o{ the

component.

TESTING

. Insert the plug into the AC supply mains and be careful

to not touch anY naked wires.. To test the level indication mechanism, place the probes

on th,r walls of the tank using one of the two ways de-

scribed above. After this placement, fill the tank at ieast

up to the MDL.. This should cause the loudspeaker to generate an

alarrn. If this does not happen then check whether

the toggle switch is in the "on" position or not' If not,

change the position of the toggle switch to hear the

alarm sound.. When the alarm is generated, it can be silenced using

the same SPDT toggle switch provided inthe circuifry'

TROUBI.ESHOOTING

If the circrit does not work as desired, the procedure

described below should be followed:e It is preferable to begin the troubleshooting process from

the output stage onwards and then proceed to the input

side. To begin, apply a voltage of 5-5 Volts to the loud'

sp€akei' ciirectly and ensqre iirat it isoperalingTi'r1;eriy

at this voltage.. Next, check the connectioru of the base, euritter and col'

lector of the transistors and whether all the resistances

being used are of the required value. Verify that you

have the right components in the right places'

. Once the circuit problems, if any, have been resolved

your water-level indicator is ready to be installed and

used!

TRY THIS OUT NEXT!

During sununer months, the problern of over-flow while

filling desert coolers is cornmon, The water-level indica-

tor described here can be iniplernented to overcome this

problem, Each time the desert cooler is filled to the brim,

the level indicator will sound the alarm and light the LED,

thereby checking the wastage of water!

CONTACT DETAILS

For a cornplete catalogue of available kits, visit oru web'

site: wvrw, kitnsPares.coln

Docwnented by Aditi Goswami

@ Kits'n'Spares