Electronics Projects Vol. 14 8188152072, 9788188152070

Table of contents :
LED Speedometer ..............3
Walkman Radio Player ..............5
HighPower Stereo Integrated Amplifier ..............7
CountDown Timer ..............13
The New Generation Stethoscope ..............18
Cordless Remote Control ..............22
Infrared Proximity Sensor ..............25
AddOn Devices For Multimeter ..............28

Citation preview

Electronics Projects Vol. 14

EFY Books & Publications

FOR YOU

EFY is a reputed information house, specialising in electronics and information technology magazines. It also publishes directories and books on several topics. Its current p ublications are: (A) CONSTRUCTION P ROJECTS l. 2.

3. 4.

Electronics Projects, Vol. 1: A compilation of selected construction projects and circuit ideas published in Electronics For You magazines during 1979 and 1980. Electronics Projects, Vol. 2 to 19 (E nglish version) : Yearly compilations (1981 to 1998) of interesting and useful construction projects and circuit ideas published in Electronics For You. Electronics Projects, Vol. 20, 2 1 a nd 22 (with CD): Yearly compilations (1999 to 2001). Electronics Projects, Vol. J 6 ~ ~) :Yearly compilations ( 1995) of interesting and useful construction projects and circuit ideas published in Electronics For You.

Rs 120

Rs 120 (each) Rs 150 (each) Rs 95

(B) OTHER BOOKS l. Learn to Use Microprocessors (with floppy): B y K. Padmanabhan and S. Anantbi (fourth enlarged edition). 2. 3.

Rs 180

An EFY publication w ith floppy disk. Extremely useful for the study of 8-bit processors at minimum expense. ABC of Amateur Radio and Citizen Band : Authored by Rajesh Verma, VU2RVM, it deals exhaustively with the subject- giving a lot of practical information, besides theory. Batteries : B y D. Yenkatasubbiah. Describes the ins and outs of almost all types of batteries used in electronic appliances.

(C) DrRECTORIES l. EFY Annual Guide: Includes Directory oflndian manufacturing and d i tributing units, Buyers' Guide and lndex of Brand Nam es, plus lots of other useful information. 2. 'i.t. 'Directory: First comprehensive directory on IT industry covering hardware, software, telecom, dotcom and training institues. 3. Tech n ical Educalional Directory: Includes course-wise and state/c ity-wise listings of technical educational institutes in lndia, besides the alphabetical main directory offering all the relevant information about them.

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(D) MAGAZINES I. Electronics For You (EFY): In regular publication since 1969, EFY is the natural choice for the entire Rs 60 (with CD) electronics fraternity, be it the businessmen, industry professionals or hobbyists. From microcontrollers to Rs 30 (without CD) D VD players, from PCB designing software to UPS systems, all are covered every month in EFY. 2. Linux For You (LFY): Asia's fi rst magazine on Linux. Completely dedicated to the Open Source community. Rs 100 (with CD) Regnlar columns by Open Source evangelists. With columns focused for newbies, power users and developers, LFY is religiously read by IT implementers and CXOs every month. 3. 'i.t. '(Information Technology): A monthly magazine for 'Techies ' and those who want to be. Its readers have Rs 50(with CD) two things in common-a background related to IT and the thirst to know more. Topics covered boast technical depth and aim to assist in better usage of IT in organisations. 4. Facts For You: A monthly magazine on business and economic affairs. It a.ims to update the top decisio n makers Rs 50 on key industry trends through its regular assortment of Market Surveys and other important infor mation. 5. ePower: Published every alternate month for the electronic-power industry, primarily consists of all e lectronic Rs 50 power-supply equipment, and their related component and services_A must read for those in this indu try and those catering to it. 6. BencflT: A technology magazine for businessmen explaining how they can benefit from IT. Rs 20

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For retail or ders:

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360

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ELECTRONICS PROJECTS VOL.14

EFY ISO 9001 :2000 CERTIFIED

SINCERELY YOURS

EFY Enterprises Pvt Ltd D-87/1 Okhla Industrial Area, Phase-1 New Delhi 110020

© EFY Enterprises Pvt Ltd. 1997 First Published in this Edition, 1998 Second Edition, July 2000 Third Edition, February 2003 Reprinted in 2006

All rights reserved. No part of this book may be reproduced in any form without the written permission of the publishers. ISBN 81-88152-07-2

Published by Ramesh Chopra for EFY Enterprises Pvt Ltd, D-87/1, Okhla Industrial Area, Phase-1, New Delhi 110020. Typeset at EFY Enterprises Pvt Ltd and Printed at Nutech Photolithographers, B-38, Okhla Industrial Area, Phase-1, New Delhi 110020

FOREWORD This volume of Electronics Projects is the twenty second in the series published by EFY Enterprises Pvt Ltd. It is a compilation of 24 construction projects and 77 circuit ideas published in 'Electronics For You' magazine during 1993. In keeping with the past trend, all relevant modifications, corrections and additions sent by the readers and authors have been incorporated in the articles. Queries from readers along with the replies from authors! EFY have also been published towards the end of relevant articles. It is a sincere endeavour on our part to make each project as error-free and comprehensive as possible. However, EFY cannot resume any responsibility if readers are unable to make a circuit successfully, for whatever reason. This collection of a large number of tested circuit ideas and construction projects in a handy volume would provide all classes of electronics enthusiasts-be they students, teachers, hobbyists or professionals-with a valuable source of electronic circuits, which can be fabricated using readily -available and reasonably-priced components. These circuits could either be used independently or in combination with other circuits, described in this and other volumes. We are sure that this volume, like its predecessors, will generate tremendous interest among its readers.

CO TE .TS

Section A: Construction frojects

I.

LED Speedometer ....................................................................................................... 3

2.

Walkm·an Radio Player ................................................................................................ 5

3..

High-Power Stereo lnteg,tated Amplifier ................................................................... 1

4.

Count-Down Timer .................................................................................................... 13

5.

The New Generation Stethoscope .............................................................................. 18

6.

Cordless Re·moi.e Control ............................................................................................. 22

7.

l'ntrared

8.

Add-On Devicecs For Multimeter ............................................................................... 2.8

9.

Multichannel Fire Alarm Sy tem .............................................................................. 31

I0. 11.

Tran. former Testsr ....................................................................................................... 35 Emergency Light Using 23cm Fluorescent Tube ....................................................... 37

12.

Touch-Operated Dig'i1al Volume Control ..................................................................... 40

13.

Kenle1imer ............................................................................................................... 43

l4.

Auto Protection For Refrigera1or ............................................................................... 46

Proximity Sen or .. ._ ....................................................................................... 25

IS ,

Watchdog For Your Mains .......................................................................................... 49

l6.

A Portable Data L-0gger ............................................................................................. 52

17.

Revolving Seconds Disp:lay ....................................................................................... 56

l8.

Automatic Porch L.ig.hl Cum Doorphone ...........................................,....................... 62

l9.

lOOW Power Amplifier ............................................................................................... 66

20.

Automatic Freque-ncy Counter ...................................................................................... 71

2 l.

Multistation hn.ercom .................................................................................................. 75

22.

Autocue For The Speaker Who Won 'l Stop .............................................................. 79

23.

A Unique Christmas Star .............................................................................................. 83

24.

Electronic Tanpura ..............,,,...................................................................................... 85

Sec1ion B: Circuit Ideas l.

Infrared Remote Con.1roltSwitch ................................................................................ 91

2.

Two-ln~One

3.

fire Al.am1 ................................................................................................................... 93.

4.

Electronic Calender .................................................................................................... 92:

Emergency Light ..................................................................................... 92

5.

Lamp Intensity Controller .......................................................................................... 93

6.

Power Failure Indicator .............................................................................................. 95

7.

Feather-Touch Swi1ching Por Battery Operated Equipment ...................................... 97

8.

Crystal Go-No·Go Tester ........................................................................................... 97

9.

Fluid Level Monitor ..................................................................................................... 98

JO.

Digital Volum.e Control .............................................................................................. 99

l 1.

Battery Eliminator .....................................,.................................................................. I 00

12. 14.

Super Simple Jntc::rcom ............................................................................................... JOO Programmable Digi1al Staircase Generator ............................................................... 102 Disco Light Without Transformer ............................................................................... I03

15.

20 + 20W Ster.::o Ampl!Cier ............................................................................................. I 04

l6. 17.

Continuity Tester Cum Capacitance MeteT ............................................................... 1OS Loud Ringing and Blinking Ligh( For Telephone System ......................................... 105

18.

Emergency Light with Charger .................................................................................. l06

19.

Car Hom with Hiedi. SongTuoe ................................................................................ l07

20.

Tempennure Alarm ..................................................................................................... 107

21.

Mail lndica1oc .............................................................................................................. 108

22.

FM Receiver ................................................................................................................ 109

23.

lnexpiensh1e Bar Ge:nerator ..............................................., .......................................... J lO

24.

Manual Morse Code Gener:itor .......................................... :......................................, l l 0

25.

Phase Sequence Detector aud Decoupler .................................................................. 111

26.

Superb Equaliser ........................................................................................................ 113

27.

Musical Sound Generator ............................................................................................... 113

28.

Speech Preparator ...................................................................................................... 114

29.

Background Noi e Filter ............................................................................................. 115

30.

Component Te.ster ...................................................................................................... 116

3L

Solidstate ErnetgMcy Power Supply Unit ................................................................. I.17

32.

Fully Eleclronic Con.trolled Vohage Stabiliser .......................................................... l l8

33.

DualToneSiren ........................................................................................................... 119

13.

34.

Phase Difference Measurement Using Phase Locked Loop ...................................... J19

35.

Safely Indicator form. Circuits ............................................................................... 121

36.

Pan;im.oniu Twilight Switch ....................................................................................... J2 l

37.

Hi-Fi lnteroom Cum FM Transmluer .......,, ................................................................. l 22

38.

Safety Switch,, ............................................................................................................... 123

39.

Two in One Game .......................................................................................................... 123

40..

Digital Speed Co111rol of DC Molor ......................................................................... 124

41 .

Speed Controller for DC Micro Motor ....................................................................... 126

42.

Security Systc.ms for Cars ........................................................................................... 127

43.

Mini Advertisemcni Dis,play .........................................,,................................................. l28 Automatic Toilet Lamp .................................., .......,,.................................................... 129

44.

4S. 46.

2 + 2 Watt Stereo Amplifier ....................................................................................... 130

41.

Fax Guard ............................................................,,........ ,............................................... 132.

48.

Auto Power-Off for TV .......................................................................................... ,, .. 132

49.

Touch Controlled Alarm ............................................................................................ 133

so. 51.

DigjtaJ High-Low Game .................................................................................. ,........... 134 Multi-mode Sequential Lights .................................................................................... 135

52.

Auto Level 'Graph ....................................................................................... , .............., .. 137

.53.

Touch Volume Control ................................................................................................ 138

54. 55.

DC Motor Direction Controller .................................................................................. 139'

56.

IC SSS Tes(er, Indicator Cum Disco Light ................................................................. 141

57.

Precision Under/Over Frequency Alann .................................................................... 142

58.

Autorn.atic Speed Changing Counter .......................... , ............... , ............................... 143 The l fnique De-Thumper ............................................................, ............................... 144

59.

Automatic Control for Outdoor Lights ...................................................................... 13 l

An Inexpensive l44 MHz RF Source ........................................................................ 140

60. ,61.

Pulse Generator with Four Independent Controls ...................................................... 146

62.

Programmable Organ ............................................................... ,,................................. 147

A St.able B.fO for A:mateurs .......................................................................................... 145

65.

Simp!e Hi-Fi Headphone. Amplifier ........................................................................... 147' 20-Rung Counter Using a Single 4017 ...................................................................... 148 Low-Cost CW Electronic Keyer ...................................... , ......................................... 149

66.

Ferrous Metal Detecfor ... ... . ... ..... ... ...... .. .... .. ... ..... .. .. .. ...... ........ .... .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 150

67.

On/Off Remote Control Switch .................................................................................. J 51

68.

Sleep Timer with Alarm ............................................................................................. 152

69.

Single to Du.al-Trace Oscilloscope ~onvertor ........................................................... 154

70.

Elec!ronic Plant Watering .......................... , ....,, .......................................................... 154

71.

lW Amplifier for Touch Organ .................................................................................. l 56

72.

CMOS Transistor Diode Tester ....................................... , ......................................... 156

73.

Water Level Indicator And Controller ....................................................................... .157

74.

75.

Audio-Visual Telephone Indicator ............................, .................................................. 159 Time !Divis.ion Muhiplier using Multiplexer .............................................................. 159

76.

Square-Triangular Wave Generator ............................................................................. 160

77.

A Versatile Rhytllm Aid .................... .... .. ........ .... .. .. .. .. .. .. ............ .... .. .... .. .. .. .. ....... .... .. J6 l

63. 64.

SECTION A: CONSTRUCTION PROJECTS

LED Speedometer Amrit Bir Tiwana

The

LEU speedometer described here is moreoo.nvenienlly interpretable and 1JSefu~ as far as the purpose of a

Bas.ic lclea

q:uen.cy and using a frequency-lo-voltage converter to convert i.I into a line-

The basic idea is to utilise tile fact

that in every ga.5oline oombustion en-

speedometer is concerned, in compari- gine the ignition signal at the con1act son lO bolb the crammed scale ana~· break.er (CB) po:in.1 terminal is d:ireclly logue meler and the seven-segment proportional IO the RPM (revolutions per minute) oflhe cng_ine•.This s~o­ digital.one. meterworks by obtaining lhi5 basic freA preset 11-segment graphical display changes in steps with every unit

PARTS LIST

(or say, 8 kmph) increase in speed. It has atwo-mode city and highway overspeeding alarm, which beeps whenever

101

- LM2917 F-V converter

an attempt is made to cross the safe

IC2:

-

Tl Dl

driver - .BC557 pnp trAn.:i.t.or - 1N914 •ilicon diode

D,2

-

speed limits. (It's worth reminding that 87 per cent of road mishaps worldwide occur due to unnoticed overspeeding.)

1be oo~our coding system used enhances instant. interpreLatjon by lhe driver. 1l1C present design is meant for cars and mobikes having 4-stroke, 4-cylinder engines and a 12-volt electrical system. b·ut it can T

CJreuit

switch and fed to tbe power amplifier

The ciroliil is built around dual op-

through volume controls. The circuit is

amp ICs TDA2822 and 1A316l. IDA2822 can deliver 250 mW power intoeacbchaonet It works well even at voltages as low as 3V. Its no-signal current drain is sufficiently low for the two penlight cells used to power the

sclf-explanatofY and as such its work-

ing need not bC emphasised much.

Construction AsTDA2822andlA31.61 are8-pin

ICs and YS414 is a 3-pin IC, the , Fla. 2: PCB pattern.

RT 100Q

IC3 TOA2822

__.......__..

.....

...,

IC1 LA3181 8 Ct 1~

CZ

CS

0.001,

0.001..

10V

• 04 10p IOY

1

2

3'

PIH OONFIGl;R\llON

OFICVS.t•

Fis:. 1: Circuit diagram.

PARTS LIST &micorUJuctorB: ICl LA8161 duel op-amp JC IC2 - YS414 RF IC IC3 - TDA2822 du.al op-amp IC

Suit.able meob.niim Suit.ab!.. ubinei 3mmredlED 250-ohm stereo pleyb8ck head

circuit is very compact. ft can be assembJed on a gen-.:raJ-purposc PCD or on the PCB whose pattem is given in

' Fig.2. Connect the motor to the supply

raits. Connect the battery through leaf switd'I filled on lhe medianism. Ground , the mechanism properly.

Rtaistora (all 1 /4W, :S'J&. carbon unk6.3 slatttl' otlurwiu): Rl, R2 12.Jdl.ohm l~hm R3,.R6 R4, RS. R9 100-kilolun

The LED shown in the circuit is a Jmm rebm

VRl, VR2

10.kilohm log

Copadiors: Cl,C4 C2,C3 C5,C6 C7,C8 C9-Cll C12, Cl3 Cl4 Cl5 Cl6

be replaced by 2N414 integrated circuit.

0 l {}µF, lOVelectrolytic O.OOlp.f' cenmic di.le 47~.

1'°Ve1ectro)ytic

0.02"1' ~ninue diac lµ}', :tOVelectrolytic lOOJ&F, lOV electro)Ytic 0.0lµF ceramic disc 365pF~g

0.1,.F ceramic disc

.MiaceUaneoua: Sl S2

DPDT switch

Ll

MW antelllla coil Two S-ohm loud.9peaken

~a!11witch

Author's Comments ln response to severa• letters received ftom EFY readere regarding my construction project ·W alkman Radio Player' publiehed in Jan.'98 issue, I am pleased to give below some clarifications: 1. Please connect t.ogether pins 5 and. 8 of IC TDA2822 and ground them through a tµF, 6.SV capacitor. This can be easily achieved from the track side. 2. Lear~awitch connections can be made aa ehown in the figure below. not purchase it separately You unlese it does not flt int.o the deck mechanism.

need

------o -

•

l.EN'-SW1TOH

TN'E

6l•a•a•;1•1s•ct'NH•'•at1!@'''

3. Tuning capacitor i$ 2X gang I 7. Radio circuit usesnolFTs,coUs and the antenna ooil is comll)ercially etc because IC YS414 does not work .available MW antenna. coil used for . on auperhet principle. It directly de· pocket radios. Winding your own coil modulates the tuned RF at t.be input. ia not advisable. The circuit is not very eeoaitive 4. TDA2&22 can drive any imped- and cannot be improved. But it re· ance more than 4-ohms. Thus, any · oeives local stations with high fidelspeaker of your choice can be used. ity. The power consumption of the . 5. UseofdualpotforVRlandVR2 circuit largely depends upon the rnot.or is recommended although single pots ·used. Using recording facility c~ can aleo be used. the basic idea of the project. 6. Tone control can be achie-ved by 1

using neg.ative feedback for high fre- ' quencies as shown below.

1r_;~TO::~N8

y4711

2211(

A.1 tOQ C,1 1·~

1.,,. 10\I'

T .S. SHANKAR

Hyd.e rabad

High-Power Stereo Integrated Amplifier T.S Shankar A n integrated amplifier is a higbpower, hi-fi stereo amp]jfi.er whi.c h includes various preamplifiecs for different input sources with correspo.nding exact equalisation. An integrated amplifier can accept any type of input as it bas in-buill preamp~ifiers for matchimg the inputs wilh respect to various parametets like .input impedance, inpul signal level, and equalisation jo accordance

of them are not 'complete• and only exploit the func1io11 of some ICs or show tbe basic layout of the circuit. None of them can be treated equal 10

those marketed by reputed companies like Sony, National, Philips etc. What is requited now is a 'fUll-fledgcd' power

amplifier which is in no way inforior lo those available ready-made. SudJ rcadymadc amplifiers arc incredibly expen· witb international standards. The dis~ sivc, costing Rs 3000 lo Rs 6000. Their tonion lev·e l at PMPO is as low as 0.1 price is clearly beyond the reaclt of an per cent. and signal-to-noise ratio as average enthusiast. high as 70 dB. Keeping in view the above~men. Till now EFY has seen many power tioned points, a complete pmject on a amplifier circuits and prQjects. but most high-power stereo integrateCI amplifier PHONO

PHOHO

INPUT

PAEAMPUAE.R

is presented here.

The main features ofthe projeot are high-power output of 300W PMPO, four pream.plifiers wi.th requisite equalisation networks, bass~ treble and loudness controls and equaliser connections. The preamplifiers acoept. volLagcs sci by international standards at. input impedance of 47 kilohm . The signal-lo-noise ratio is greater than. 70 dB and the total harmonic distortion is less than 0.1 pe-r cent at rated PMPO. The am plificrs arc based on integrated circuits, resulting in bigb reUability and small space consumption.

TAPE

INPIJT

Ml¢ ~ ll'ff'UT~ Tt.t4EAo--1 TUNER 11'.PUT PRE/IMF'UFIER

I

TO EOUA1.1$ER FROM EQUALISER

-1-o • r

COMPENSATING Ml'UFIEA

COMPACT DISC

VOL-UME OONTAOL

COMPllCT DISC NETWOFIK 1------~

fNF'UT AUXll.LAAY INPUT

MU.lu.ARY

NE'IWOAK

f

POWER AMPLIFIER

LS ~

POWER SUPPLY '01'/ AC

Fi,1. h Blot'.k diagram.

©

0

O>

- r

.•. ~

~ ~ ~ ·· " l..:.. ~rt ~~~~~-r~~~~:;::;·-~~~~~~~~~~E'i\·tr ....,

Ail

~

~

r;

Cl Op

!:t

'l!N

0

a

;;

i 1

...... -

n,.

1SV

:f

$t 1 i. .. ••

T ADC lll\

~, K\I

RM

RM

li!Cllll

9.1K

I I

'°" ~

~~

II

2!!'1 ..,~

{,

RIO 41K

C2I

''•

~

A42 1!5(11(

471\ ·

.....

I

1211

f'4l

11)1)1(

11

rfi'S

a - ..._..._

054

22R

~f(--11~~

I

AUll.M

I et0I R4iel

1-

lK

47'
es wi1h gangued Jevers.. Eight-

TO 12V•().12

61\ SEC. ~SFOAMeR ------~---~

04

position, soft~pusb swit.c ilts are .available which are used for dlannel selection in colour TV .sets. Use of' such switches would be suit.able.

AC

----o

-16V

23()'11

coo 0..lp

Flg. 5: Circuit.for the power supply.

C81 •100..

.. 2$V

.ov

Compenll'ting ampllften 'The selected signal from the function selector· switoh is linked to the equaliser input ports. The equaliser output from the ports. is given to tne compensating ampUfiers. A DPDT swltcb is provided bypass the equal-

to

lf ·. IJ

®@®®0

TO

EOW.USERO---

l'"AOM _ l!OUAUSE.A oO- --+---0

1

FAOM

EOW.uSER @

~...Ui!IU»IY

--Iytic

S3,S4

SPDT elide switch DPDT toggle 11owitch Push-to-on ~k:h

S5

DPST alide avntch 6V:..0~6V, 100~00m.A

tramformer 6V, 100-t:lhm relay 8-ohm speaker

24!.EDe

•

00

:2

and

oompr·omiseamongaccuracy.cost;and

shows the block diagram. The l·min./ i sec. clock pulses generated by an IC are counted by a units counter in the

•

accu~ate

guarante.ed results. For this, we have to spend more on crysral and ICs which will raise the component count too. To

Circu•1

10UN1:$

07

I

LEO OISPl.A'1

09 I

...

.,

'

:

-

M~IJaneoU3.'

RLl

divider ICs can give

The circuit is straigbtforward. Fig. I

Rh2, Rl7,

Xl

drift in frequency makes the total Ume inaccurate .. Qystal accompanied wi.lh

vance warning circuit can be easily wired.

1 ,

S2

Transistors, digital gates, IC 5S5s

can produce sec. and min. clock: pulses. But they are not stable enough and a

By selecliog an analogue display readout two !Cs (onwit i:-i ·6Mi•iec6lcl u pw·QOITec:lll"S ~UICI by the ,IAllO'· Yci another non-medicinal use of this ~et ho5copc id t • mic vibrations. which it om track efficiently.

...., C1

Readers' Comments

+

+

_{'

As• liledical student I was pleased to aee the stethoecope ~t in March

WI

'9S ieeue.

y

AHTENNA COii,.

How~r, the requirement of 12V for the circuit Jleducee ita portability; Can it bemoditied auch that it .ma,y be powered by 3V inatead? SANGRAM PII.ARE

°"FE~

AOO

KoJh.apur

acan the circuit be tranaf'ormed to a

oordleee atetboecope by adding a suit' able transmitter? The author may please describe the pick·upcartridpand inform from ~here it can be obl.ained,.and.alwbat eo&t. PYARE MOHAN SAHA!

Gorakhpur a Please C!arlfy;

1. The loudspeaker's impedance value is given as 8 o}un.8 but in part.a list it ie m.e ntioned as 8W ceramic tpeaker. What~ ita uactapeci.fica. tiona in terms of cone diamet.er, coil impedance, power handling capacity and brand name of the apeaker used

in author's proto~ype?

·

2. How to mount ·o r fix the crystal cartridge pick-up. Is an Indian. ca~ tridge available?

3. In Fip 2and 3 thevalueofRlO U. written as lOM but in part& list RlO's value is m.enti.oned as !Ok. Which is correct?' •tWbatis the outputoftheamplifter when IC LMS&O ia used without 'eat.ink? With aeuitable b.e atsink it is about 2.5 watts RMS into an 8-ohm speaker. 5. How can. a volume control be incorporated in the eircui t? S.LAXMAN RAO Hyderah$d

LO metres and its reception clarity is quite satisfactory. . Pick-up.cartridge used in my proto• type was from an old turntable !Sony ! 1229). However., other makes available with HMV o.r Murphy dealers should work . These cost around Rs 75. The entire module, including trans• .mitter, should cost about Rs 400. The value of :resistor RIO is lOM , and not lOk; the impedance ·o f tne speaker is 8 ohms (not 8W). 'Ihe speaker must have a very loose oone and of sufftcient diaMeter.

~

C7

TO REST OF

THE.CIFICUT 10K

.l~ating

volume .control.

Londe:x.·Orf.hofon make cartridge used in the prototype is readily available. A volume control ean be inoo:rporated in the circuit &a shown above.

Tu C1uthor, Mr R.Sharath Kumar, rtpl~a:

Power consu.m ption oC the circuit It is oonch1ded from the feedback tlom being greater than the usual 50 mA, readers lhat lhe pickup canridge is uee of dry celle ie not recommended I scarce to proc~ and he.nee die circuit toroperation. HO'W'e'Yet, a rechargeable needs to be modified using comrnonJy batte.ry pack (such M .iJed electttilyte available piezoelectric mjc. for which or Ni•Cd) ma.y be used ior portability. the circcujl 1s as shown here. A simple transmitter circuit for This circuit offers 3db flat response cordleM operation ia shown below. over the range ISO Hz to I0.000 Hz. The Thie transmitter has a range of about outpul may be connected 10 an eat·

phone of2=60(X}, R=2000, into which it can deliver 0.9 mWatt of power. Else the output can be wired to the inpuc. sraae of th.e low pass filter in the main c.in:uit published in the Marc:h' 93 issue of EFY. . The presets VR I, .is for power adjustments wh.ile VR2, is a volume control. The mic used in the prolotype was a "SONY" make. .

Cordless Remote Control Pradip ~umar Bose R emote oontrol cbo.dlS form very PARTS LIST interesting projects as they control aoy electronic or eleciromcd:laokal ,equi.p- Semiconductors: Tl BF194B npn tn:ins.iator mentby radio waves.You perb.aJJ5 bave 'f'2.T4, used a remote conlrol unit for 1Vs, T6,.T7 BC148B npn t.muietor AC128 or AC188 pnp VCRs or VCPs etc and experienced the T5 transistor convenience they offer. D1 0A79 or lN34 detector For a remote control syst«n two diode gadgets are necessary, namely, a 02 lN-4001 r~tifi.e:r diode transmitter and a receiv,er. Block diagrams of a transmitter and a receiver Resi.stONJ (all 114.W, =5% oarbori unkss stated otherwise): of a cordless remote cxn:nrol are shown Rl, RU .f,7-kilohm in Ft,g. 1. R2 - 150-obm

R3

R7,Rl2 R5,R8

220-kilohm 10-kilohm

R9

2.2-kilohm

mo R~.3

Capacitora.: Cl

C2 C3

C4.C5

C7

cs

F•• 1; Bloek diagrams of transmitter and rece[ver.

Fig. 2: Clrcult diagnm of the traMmUkr for eordless nmok control. 22 11911'1il•lQl[t1p;Jell!l!l~1!@111

0.0,lµF C!lramic l µF, lOV electrolytic 0.lµF ceramic o.0>11,µF eeramic l OOOµF, 25V ~lectrolytic

ClO

PVC(2X)png

C6

lOOpF trimmer

RLl

LOAD

IOO·kilohm

Cll

:x.1 RELAY

•7~

100,.J', l2Vel~trolytie 0.022µ.F' ceramic 0.047µF eePt"Jmic

C9

Miscella1teous: Ll,L2

AF

AMPLIFIER

5.6-kilcibm

IM,R6,

MW antenna coil on ferrite 'l'od 6V 4SPDT) relay (2X.)

3V driver tr.an.Conner Telescopic an~nna

The tra·nsm itter ig,. 2 represents the transmitter circuit. ln this circuit T3 and T4 fonn

a free· running or astable !Dultivibrator. ~ hqueocy

of the a;cillator i'l around

lkffz. Tnmsislot T2 is used as an amplifier. ~ signal obtained from T2 is fed to a 3V driver transform«. Finally, the audio signal is :fed to Tl for modulation. Tl also generates canier frcqu.cocy. 1be modulated RF

•fl/

T7

llC148

12 YN

output is transmitted by an antenoa.

TMrecefwr

RID 470

Hg. 3 shows the circuit or a ~ivcr. It ()()mists O·f two parts. Transistor TI

and tbeas.sociated LC circuit is used as a radio wave receiving section. TS and T6 are used as relay driver. The radio "!'!!Ves are received by the receiver

.

F~.

SPOT ONO

RS.AV

.,. Fil. 3: Clrcuit dlaa m orthe rtttlwer ror cordless remote co11tro!.

.'!.J_ •

F•. 6: Aduat..ia PCB.layout tor the clrco:lt sliown In Fia. 3.

conduction. This cooductioo charges capacitor C8. It provides proper bias forTS and T6. The relay thus operates

R1$

IOOt
sent, he ehouldcheck tr.a nsistor Tl. Mr Mahavinhould check tra:nsis.tra T$ and T7 and diodes D 1 and 02 for finding out the pr-oblem. In the circuit diagram, T'5 ahould be AC12& or.AC!.88. Cape.cito.r 09 should be o.f 0.22 µF white Cl1 ah.ould be a PVC 2x ·gang. The transmitter circuit produces

radio frequency interference. A small AM tuner circuit ia given abov~ for use in the receiver sect.ion.

Infrared Proximity Sensor T.S. Shankar

T

ofremo~e

he principle sensing is inac:x:essible .rcgiom 0tr b.iglMemperature utilised to detect the presence of any zones. object w:itbio the concemed pro.ximity lflfrared pro.ximity sensor, on the io lbiS infrared proximity sensor..There I OO'let hand, works on an entirely dif[erent are many occasions wben the presence principle. It uses infrared beam as the ofobjeclS in tbe prescribed proximity is detecting media. The infrared beam to be detected w.ithout actually making after being reflected by the object io coo.tact with them such as in object proximity is detected, and the 'presence' coonters, interruption counte-rs,. RPM signal :iS generated. oounters etc. Micro switches are used The block diagram is shown in Fig. widely for such purposes whose output is further amplified by a low level preamplifier and fed to t.he phaselock-loop (PLL)' detector. The outputs of PLL detector can be used for m icroprooessor interface or any other

purpose.

Tran8111itter Tue circuit diagram of an infrared proximity sensor is sbown in Fig. 2. IC3 is an NE555 timer chip used as a ~-----. OUTPtlf 11

INf'flAfU;:O

OETE.CTOO

LOW LEVEL ilM'ldRER

LOGAAITMMIC AMf'\U!l'ieR

'PiHASE LOCK LOOP 'DETECTOR

IOUTPUT 2:

9V

REGUlAlm POWER SlfflV

t8\I'

1ca a NE.555

R1t 3-31( '

• IC1 (•,b): L.A3181

Ff&. 2: Cfrc11it diagram or the infrared proximi.t)' KDSOr,

7

F... 4: CGmpooeau laJODt for the PCB allowa.bl Fla. 3.

o-I

.i

..

. ... - ~~ .. f H. fo. t. ~· I

;;" ~j

~

••

.•

'

l.

~ ·Rl4 ~

IBll

,,

rue alarm system.

........ O·

0

0

• NOTm 111E FIEMQTE SENSOR Oi ECTED Al Otl'FERENT ...... n~

~ ..... ~.

t

-

l'l'.I Q->

1 :0

..,~~

, .!'if 'f

..!Ii: t

...r '

.... ilfi .. ''~ri ssn~

0

.. . ·- 0

Fig• .3: Con1poneots laycrut for the PCB shown. In Fig. J.

a

-

o

.. I

o

-

o

0

•

•

Fig. 2: Act1tal•5Jze PCB'layout (or che circuit shown i111 f ig. l.

•

0

.

•

0

Tbe

· rcrnote buill: ~Shown in Fig. S, comprises

semior,

an IR sourc.e and IR detector,.faci.ngeadt other with provision to allow entry of smoke freely bet.w een them and X1

DH NJ PFIMN'l"I'

03

TOIV-cMN

1Ntl00l

7~ :5£(;.

obstruct. the IR rays.

As long as the lR light fa.US on the detcctnents and a bauery back.up has been .inrorporated to ensure prccisiooofthe lime settings.

The kettle timer offe·rs ase[ecti.on ot turn any electric kettle into an • seven timing delays, ranging froai three

The .kettle timer desaibed bere CID

R1 5.el( 1SW

al'--

------.1 .....~-""llfN~l1 0

IC1

CD40e0

-

VR2 allows fine adjustments. Dl, D2, R181ld Cl provide Lbe funaion a

or

transformer-Jess power .supply which 'reliably' provides 9 volts. A flat 9V, PP3 NiCd battery provides back up. It i:s ooostantJy triclcle-cbarged by R2 to

01

1N4001

.., ..

IC2 CD4017

-------a

AS

D5

10K

1H41.41

0.471&

tc3 (C)

TO ELECTRIC

KETTI£ 12

oe llN4141

0

o·

0

0

f'Jg. :t: Aot1.1at-.l'n PCB layout of th• clt~utt •hown In Fig. t. OQt remain discharged. The output pulses of IC1 are fed to IO (decimal oounter). The ourputs 03 through Q9·IJJ high after 1bree. four•..nine hO\ll'S {pulses). And depending upon whic.b output is selected via timi11g selection control Sl, 04 becomes forward

bi~ afle.r that

en.sure that it does

1

~ibly Jike Lo boil

delay and trigger triac which will tum on the kettle 1hat is connected to it as load. After the delay set by VRt, l.e. the tea making time set by the user. IC3(b) will go high. This period may be set for

conduct and tbe piezo buzzer will sound an. audible alann. At the saJne time, due to the conduction by D·5, IC3(d) will go low and turn the kettle off.

Fig. 3.: Component. ltlyout of the PCB ehown In fig. 2.

44l'!'W'iJ•lQll!18U•JIP1,.1!@'1'

up to nine minutes. (One would not tea for tbat long!) After this delay, Tl will begin. to

time de1ay. Corm;pooo·

ingly, IC3(a) will go high after that

1

Construdtfon Construction is straightforward if the ccmpact PCS shown in Fig.2 is used. The piezo buzzer may be a small 20mm type in.stead of the more common 27mm ODe.9. All oompooenis including tbe triac wiH mount ·On tbe PCB. Solder an dis· aete oomponen·is fimt, followed by the pieio buzz.er and then 1be timing selector switch (S1).

Note that a less comm.on seven-w.ay slide switch is to be used. It is available from most mail-order services that ad· veni.se io tbis magazjne. However. it may, if necessary,. be replaced by a rocary counterpart which will however oot mount on the PCB. AI;.the unit uses no transfonner, and ia quite compact, it may be installed within any :mains ou~ let strip acd oonDedt.d throu&h

its switch to the output

plug soctet. Adequate care must be latel'l to

properly. (11 can handle a maxi'.mum load of t.8 k:W.) lnsul.ale the unrt weH.

PARTS LIST &mi.conduclon: ICl - CD4!0&0 eountw, o.eillato:.IC2 - Cl>4:017 decode eount.r IC3 (a-d)

-

CD40106 iiehmitt

Th.e tmle timer needs just two adjust-

Tl

-

inverter BCS48B

Dl

-

1N4007 •ilieon diode

DS

D4··D6

-

9.lVze,ner 1N400l ailioon diode 1N4148 ailiicon •witching diode

Triae

-

TIC 225

digiml watcll to get. a pulse every bout ( 0t conveniently, to get a pulse every 15 minutes at 14 pin of IC2). :Secoad, set VRl 10 provide just enough delay for the tea to boil properly. i.e. t.o set the period for which the .kettle ·element is kepE on. This can be between a few seconds and nine minutes.

02

ments. First, set VR2 wltb any acc;ura1e

Reri&tcr• (all I J4 r.IKltt ;a;Sll> carbon unit:# 1tr;JJ.ed QtMrWiu): Rl

-

5.6-kilohm, 15 watt

R2,.R4 R3,.R5 R6

-

1-kilohm 10-kilohm [email protected]

R'7 RB·

-

2.2-:111egohm 101)-kilohm

VRt, VR2

-

500-kil.o hm pruet

Copaciton: Cl -

t70JA}', 25V elect.nilytic

-

1000.,.F, 25V

ca.

-

electrolytic lOnF, 400Vc•amic

Cf.

-

0.471jil' ceiNmic

02

ensure ahat zener D2 is perfectly 501- . Miictllan«>ld: - 1-poJ.1 7-way •wikh de#d. before testing tbe unit even 81 - 230V·.ieetric kettle ~fBHJng whk:h the mai~ may take - Pi•o l>uzz.e:r a toll of tbe IC.S. Heatsink the triac

1

II

use

I

Using it is simple. After io.staUing it as suggeQed. plug in the kettle. Suppose you want tea at 6 am n.ext morning. While going 10 bed at ten pm, sec S 1 to

8 hours and tum the power on. At siix, the timer wHit um the kettle on, prepare the brew, tum tile keUle off. aod then

sound an alarm..

0

AUTO P'ROTECTION FOR REFRIGERATOR B.S. MALIK

t has been. (ound tbat tlJe,«llJlpre&'destroyed due co very low or very bigb line voltage. As~. com~C&Dwith­ stand MO to 250 v01rs only. 'The problem arises wben. the line voltage dips below even 1.WV orriss above 250V.

I

10' of a ~frigaat« p

(The.n: is oo stabiliser jn the market wblch can seep up voltages of the order of l40V ort __,. - , _ _ _ __ ..... .,,,,...·er.)""'"&S __ HJ ' s·m _I p-1C8uueeGDOnJical citc:Uit ovenxxnes the problem.

Working 'The ciJ!CUit:bu two single-stage amplifiers built around transistors T1 and T2

which operate. relays RLl and RI.2 in-

dependently at preset line vollagc lev· ,ets. When switch Sl is tumed ,on. step. down ceof:re,.tapped transformer Xl provides 9V AC Input. This is rectified

bydiodesD5andD6,tilteredbycapaci· tor Cl and is applied to tmn,saors Tl and T'2 through bi.Wng.resistors. As,Tl

,and T2arc pop transmors. positive voltages on. their bases ma~e them rev,etse biased. Wbeo zener diodes 01 and D2 cood:uct they remove tbe ~verse base bias and the tramistorscood~ and the

reta,s ronoected to tbem (RL1 or RL2) g~t ·energised. Operating levels of Tl

and n can be set by adjusting presas VRl and VR2 rcspcctivcly. · Capacitor C2 and diode D3 avoid clmtterlng .o f relay RLl. Similarly, C3 and 04 prevent cllatterin.g of relay Rl2. When volrage across zener Dl eit· ouds 8.2 V, rt conducts and reverse base bias of Tl is removed. Relay Rl.1 g~ls energised due to Tt"s conduction. So contads. of RLl complete the. Jive Jioe (phase) path up to load. As neutraJ line of load is directly amnected to

mains line, the load (refrigerator) gets supply and panel mecer indicates the line vo.ltage. When neon bulb (green) St

,....._

ON/OFF SNITCH __.,.er-~

R3

U\IE

f

toa 0>$W

2301/

11N

T1 AC12111

ID2

12\1 ZENER

NELJTRAL M;

VOLTMET'ER: 'l:!nl IC. PRIMNW

TO W.f>.W 500mA.

sec. TRA.NSf'OAMER

R7 IOOK

2AFUSE UVE

GREEN

NEON TO

REFRla&AATOA

'Fig. 1: atc&&ft.dlegram of auto protection fOf RfiigeqtOI'.

46 l1911'1il•lQl[t1p;Jell!l!l~1!@111

~

X> lSOV

PARTS UST

LiOClll"""'rn:

·n,n .

-

D1 D2 ~(rill .l

ACI7BJ11Wpnauhu:n

down die volt·

~:t

age When relay RLl eocrg)ses. F:tnd. Ol.lt volta,ge dJffe:rel'X'I! be· tween tbc cner-

IR *'511> owbM. MkN

"'*'~ llt,B2 - 27~ B8 B4 as

-

:22:.ohm, o.5-tt

R.7, R8

100-lcilobm 10-kilobm p-eM

VBl, VB2 ~

-

~7a.J', 25V et.ctro),ytie 4.1!ll',26Vttec~!ytie:

JI~

RLl,BL2

Xl SI

era111n1 voJt-

~ ~.&-kilohm

.100-ohm. 0.5 wau

Cl C2,.C3

Pini am deco-

lo.ohm, 0.6-tt

:18

250-obm, 9-vcilt, M

•insle cont.at Nlay 9V.0.9V, 500mA •tepdown t"ra:naformu

On/of!•witeb.

Red.DllOU bulb Gnen uon bulb

2.Afu.M

Vokm.tu o..aoov AC Fu.e,2A

g1ows, it lndia.ies that load voUage is wjlhin proper l i11>ils. When line voltage faJJsbcla.v 16.W, 1ransi~orT1 stopi;conductingandrelay RLl deenetgiscs, and discon.nects the load. Hence, the 1refrigerator does not get the. low su,pply aoo is safe. Wb"11inevoltage increasesbeyond 2SOV. uner D~ conducis and revcrsc base bias ofT2 i..s re.moved. So noon·dUd.s and Rl2 energises, disc.onnecting liveline·(phase). Neon bulb (red) glows,

ii

slowly. Note

8..2Vl*Dt1' 12VMDM 1N4007 .wcon ell*

08-DS

rm dlel1

Increase

ages.. It SbouJd be minitm1m. For a particular ,. Sdting jt may be ,.. ~: ~ponenia layout .W. otthe.JICB. ehown Ill Fig. 2. about SY. Simile:dy, inaeme line voltage ·up indkal~ng improper liac vol.iage. Jri Ibis ' way lhe load does not pl supp~y and is to 2SOV and adjrust preset VRZ to eper· g:ise relay RL2. When it energises, insafe agaillSI high voltage also. Tripping poin,is of relays RLl and aease the v·oltag.e up to 260V and then RL2 cao be sc:t by prcKls VRl and VR2 mlwc it &lowJy, lli:id note down 1he at 1t@W

The~

tenninalS of the counter:s

are wired 1oge1ber 10 a reset switch ($3). When. this swi:tch is.activated, the oountcrs are reset and in tum reset the dock. Tue address is then sequentially produced. The bin.My counters have

trigger al high-to-low Hansitioo of the clock and the other at low-to-high transition. Complement oulput Q of t:he former is fed directly to WR input of

recordct; as may b~ «:quired. A simple seven-segment display wi.lh a pair of decodcis could also 00 used to direcll~ read the data in each address

state.

Any t ransduced sign~l could hence be sam.plec. and.lo~ed~in ..Though the mem~ry capacily ts limited and the scanning speed reasonable, the equip~ m~nt ~ou1d prove handy for the field sc1~nl1Sl '. The unit is simple and can be butll eas1ly by a hobbyist to learn about lhe ~of AD~ and RAM dli(li. thmJgh expenmentmton.

the ADC. This is the st.an of conver- loc.auon. The unit is ~wercd by a regulated sion signal 10 the ADC and. occurs +5V . DC derived from a smal1active low inpu18and so the address bils al lhe same instant the address is s1i.ed 12V accumulator and a 780S . changed. The A· D conversion isstartc.d dlange at every bigh·IO-low transition regulator Chip. lbe drcuit. wilh the and the data is placed on the data ; of the clock pulse. Wben all the addllCSS power supply can be carried a a shoulbus wbile · t he clock i still in the low locations are exhausted, the Qc of the der pac:.k.

dtlrd counter goes high which stops the doct and thus the scanning. addttss lines through a set of 7404 inverters. An external triggercould al.so lie put-in, instead of th.c clock output,

The Q outplll1 ofsecond monoslabl.c is connected as shown to TPDTswitch (Sl) whiCh selects the 4 read' or 'wrile' opl.ions. When the swilch. is Lhrown to the 'write• position, lhis signal is fed to both the CS and WE of the RAM chips.

through.the socket sllown. This. would prove useful" when :recording an analoglJC: signal at events specified by this

bus into the RAM.

. The address locations arc dlsplay·ed by aa arra1y of .L EDs driven by the

trigger.

The hardware control bus The dual retriggerable monostable . ml.Jltivibrator74123 .is use.cl to produce lbe control signals for the system. The clock output is fed to both the monostable mullivibrators. but one is set to

During low -to-high transition of the clock, this writes the data in the data

1

During the 'read· mooe this signal

Tile same circuit logic coutd be used 10

is dioonnecled from the RAM chips by the TPDT switch. The switch throw's CS t.o low and WE to high, thus f~cili­

b~ild. a CMOS up~adalion ·orthcex.isting

tating the RAM to dump data into the bus. The read data can be fed in paraltel

to a mkrocornpul.er or ·t hrough a (digital•tG-analogue) ~vcrtcr to an X-Y

c1rcuu. A 6116mplaceofthe21 'l 4s a

single CMOS 4040 counter in place ~f 7493s and a CMOS monostable. could be used to upgrade it to a low power vcrs.ion with 2k memory .

R.EVOLVING SECONDS DISPLAY S. BATRA

S

ome time ago a·circu..it f°': disof seooocrs was published in BFY which used cxtanal muJti; plexing. This addition. .increased lbc number of displayed digits to six. Hence• . the disp.lay and sbape of the cloct t» came very long. play

A new approach has been Uied here lhroughananaloguedisplay·o fseconds aloog the periphery of a circular ana. logue dial. with a 4-digit dis:play in the centre, .~ shown in Fig. 2. ThIB design gives an .attractive look: to the cloo'k besides the novelty of a revolv.ing sec.onds d~lay. This project b~ to be used in con-

junction with a digital clock. The recommended PCB layout therefore. reserves lhespaoe for the clock circuit as, well.

Principle Theprincl,ple of the project l~explai·ned

Fl9. 1: Blocfl dlligram of revoMng ..cond• d'l•play.

, in the block: diagram shown in Fig. l. The dial is div.i

)(1

Z»V IC PRIMARY TOIZV~ 12V 0.5ASE£. .

~

Fig. 4: A typkat dlghal Qlock drguh'Nlth 1h• eddltlon•l l'flt\llr.d amendment..

extended to pin 13 Qf IC!. The counter ir to respond to low-to-h igh trnnsition. wm advance when lhc iaput al pin 13 ~ soon as seventh sector pulse is regoes from 'higb' to 'low'. As the IC ceived, IC3 is reset to the first sector. works as a decoder atso, ·the dcccded Outputs 00 to QS only are utilised high output is available at QO to Q9 as wl\ich are high when a.ctivan:d. To proviCl.e tetW'n path to LEDs it is shown in the circuit diagiam (Fig. 3). The decoded outputs are extended to required th.a.t sector outputs arc low. ten rupective LEDs through the limit- _The output of sector counter is given to ingrcsistors. Thec.athodesotaU the ten IC2, a CD4069, wb:idl inverts the outLEDs are conncaed together for a puts 00 to OS. common ground. The reset switch of above two ro.Jnt• The complete display of 60 seconds ers will be operated along witb seconds is divided into six sectors of ten counts display input (pin 32) and Fast Set (pin each. The respective ls, 2sand 3s etc of 34) of clock IC (Fig. 4). First, !he secvari.ous seaois ~ mubiplexcd togelhec onds display switch will be pressed and as shown in .Fig. 3. subsequently lhe r-esc:t switch, which Pln 15 is Master Reset i:nput which

resets all the outputs 10 zero when acli· valcd by a high signal. lC3 is agaiD a CD40J7, a decade counter-cum-decoder used as a divide.

by-six counter by connecting pin S (06) to pin 15 (MR input). The sector counter receives input at pin 14 wtlich enables

ss1•a•a•;1111•ct'NH•'•at1!@'''

will extend high outputs to both the CD4017 counters and to Fast Set (pin

34)ofclockIC. Clocksecondaswellas displayedsecondwilllhusrcsdtoz:ero. D1.1ring power intcn:upttons, back· up batteries keep the internal clock circuit of clock IC active but the segment oucputs including colon output -(Ufz)

become inactive. This makes r~olving

seconds circuit jObless. After .l '§tora· Uon of the mains power invariably the synchronism or seconds display goes out with that of real dock:.

An automatic synchronisation citcuit is developed by using a diffcnntialor(l Ok resistorand 2.2µF capacitot)at pins 16 and 20 of clodc IC. Whenever 'e' or ~r segment of the mi11ute digit bcoomes active the above circuit gen-

erates a positive pulse which resets ICl and JC3. After restoration of power, when the next even mlnule appears, i.e. 0, 2, 4, 6 or 3, Ille seconds counter and scgmene counter resets with the actual minute ttan.sitlon. In other words, tbis circuit does not s.t1pply the immedjatc

solution to the problem but resolves it within two minutes (maximum).

Working Say; whcD sector 1 ~active, low output

fig, I:. ActU8I • • PCB lllyout of~~. . dhp&.1 chulJ,, Including · Ch•.t M a~cil clocl drcult.

k ·extended to common cathodes of

to LED20 wiU flash one by one at one-

blink at the cent~. the seconds display

'LEDl tbrough LEDlO. Ou1puts QO to O!>willbcoomc high one by one at onesecond intervals. As a result,. LED! ·10

scoond intervals. This will continue for ! all th.e she sectors. Hence in 60 seconds the display will •revolve• fully by 360 degrees. . The 1Hz signal is used to display :·1be eenlre of the dial also. When this signal goes low_. the central LED blinks andi tbeM50i::l4tted.second LED's g,low shifts to the next lED. Wilh every

rotates by six degrees., and hence in.one minute it completes the round.

L£01oamspoaamg to .respeai\it secands display on lhc round dial will Oasb. Similarly, after ten secondS the second seaor becom.e aatvc, ex.lcDding low outputs; to common cathodesoflPDlUoLED20.Now,UIDll

will

Power supply The total current drain of above three lCs and flashin,g LED (one at a time only)willnotcxcecd lSmA.Thismucb current can easily 'be spared by the

Fl9. I: Component. layout of revoMng clleplay wl1h th.t of• ty,plc.J dock clrcUlt.

power supply ·o f the main digital clock circuit having capacity of 300 or 500 mA at 12 volts.

PCB· As this circuit is required to be used in oonjunctioo with a digital clock circuit, the i;pace is reserved for lhe same on the PCB (l8Smm x 18Smm) (Fig. 5). The

1

60 l1911'1il•lQl[t1p;Jell!l!l~1!@111

top poruonoflhe PCB houses the majn clockcircuil, reseccircuitandautosync circuit. ·The middle po11ion oootains 40mm (djgil height) di.splay (w;ing 3 x

ar~ connected in differ,cnt rings to the corresponding sectors lbrough. jumpers, as shown in the components layout

(Fig.6.)

5mm rectangular LEDs), and the botThe PCB a«ommodates all/ lhe tom portion of the PCB contains re- components exccpr the tram:fonncr and volving secon.~ c.irouit and the powe.r set switches. 1be sw.itchcs can be

S\IP.Pl y circuit.

mounted on the RHS ·Of an acrylic cabi-

riphery of the LEDs. All these LEDs

tra~former should

The rings are drawn along the pe- nel for casy acc:ea and operation..The be mounted on the

~ of the cabinet or can be oonOCdcd outside near the mains plug as

desired.

PARTS LIST

vol'v ing seconds circuit giv~ outputs to

' Smakond~

1Cl, IC3

A.ssembly The complete cir~it should be assembled in the form of small modules io Che following steps. 1. Display cirruit 2. Oscillator/divider circuit (5369) 3. Qock Cira.tit. (8361 or 8362) 4. Revolving seconds circuit (using 31~)

5. Power supply circuit 6. Auto sync/reset circuit.

· especially when you are struggling lo locale the fault aflcrcompletingassem-

bly.

Rt.mo, RH, R&9; RAO Rll &si, RlS RU Rl5

-

I ·kilohm

-

15·kilohm

Reade.rs' Comments

- - J O-tllohm

1: megohm 100-kilohm

Rl1·RS8

oeeding to the next one. Each segm cnt of the display circuit should be ~csted b·Yextending 6 to 12 volts from the test. bench supply or 9V bait.cry along with 1 lit series resistor.

uting the frequency.

.IN

70WFE CCNECTED

TOGETHER FOR MIN. TENS

I

11111111111 '111 lllllll '*"*"' p-channel MOS

Fig. 2: AehllHla PC8

for Autocu..

on !ow thresh.old working.in enhancement made. The IC am directly driv,e 7-segrnent disp1ays up 1.0 four digits in .i ts 24~bout mode.

is found to be sufficient. However it may be tailored 'LO suit a specific case wilh a maximum resistaace of lk in

each RC chain.

frequency may not exceed five minutes

Further improvements, though not. necessary in most applications, may include a dedicated aystal-drivenUming generator circuit, as given in Hg.4. The timer chip MM5369 is a regular bedfellow of MM5387. This chip is very good at its division business. It is an 8-pin lC witb a 17-sta.ge binary divider. A rommon1y available crystal of 3.58 Miiz gives out a frequency of 60 Hz at its output. A U that is requi.red is to select ,6()Hzoption on the clock cbip. Another alternative is to tailor tbe unused half of CD4013, a D flip-flop. The second D flip-flop may be wired as a clock: generator. By timing the set and reset action of the flip-flop, a regular pulse train can. be produced. However, it would give a nonstandard frcquency1 difficult to trim lo either SO or 60 Hz. Moreover, this type of pulse generator is cbaracterisrically weak in

ln fact. 'I.he 'glo.rious

producing satisfactory short- and toog-

Usually.,.il is programed to prod a music chip to sing "happy b~rthday' •or ~'.jingle bell''. · The power romideration of ttm clock chip. voltage and its regulation etc, is · not very stringent. lbere is no need or .regulated power supply. Maximum

power dissipation does not exceed one watt. It. is better to keep the segment

drive current. within the range of 10 to 15 milliamperes. The Autocue does mate use of aJI the features stuffed in tbis chip. How to time the Autocue ? Popular belief is 1,hal the mains frequency is not

a very gocx:I source for an accurate clock timing. It has sbort-tenn instability, an Inherent weakness. Acoumulated error due to this affects the overall liming. However~ in an applicalion like ours,. lead or Lag in mains source

in ten h.ours.

uncertainties,' intensify the thrill. Auto-

term stability. Too much of 'glorious unoortainties" is not desirable. When the power .is turned on, Auto-cue wak.es up with certain stiff rules. The circuit is automatically forced into sleep modet since the sleep input.(pin. In fact, U1e lead/lag due to the mains 30) is made permanently active. (!be frequency variation is not very dreadful term sleep is a technical jargon. o pun. ascomparedtotheeffectofnoisespikes intended.) The display will flash perched on .mains voltage. When using 9(hours), 59 (minutes) at a regular inthe mains f roquency. it is to be mte-red terval. In this slate., switches S2 (slow adequately. In the prototype a chain of set) and S3 (fast. set), both normallylwo RC combinations, 22-obm/lkpF open pushbutton type. may be use.d to and .330-obm!lkpF (R2C2 and R3C3), :set a di ffereAl sLart up time. There are

-cue is not avezy good candidate to time an evenl like SO-metre sprint. Tn the Au.tooue circuir, the SOHz seleot. (pin 36) ism ade active and mains freq~ncy is applied to the clock input (pin 35).

so 1191alil•lQl[t1p;Jell!l!l~1!@'1'

I

four possible combinations resulting from the switch set-up. ;SJ

Aff controls. A circuit that slowly in- brighln~ condition the voltage across creases and decreases the brightn~ of the SCR will be very tow (very narrow lbe lamp is rare and will be ia.teresting. pulses). Only a very low current can be This type of circuit is disaJ$Cd below. To slowly increase and de.crease the

bri_gbtne§, tbe voltage applied «> the bulb should be inaeascd and decreased slowly. A ptiase controlling circuit can be med. for this.. But p.roviding the working voltage to the control circuit

1

,coosumption of the oorurol cirruit should be minimum. That iS why tbe mul'!.ivi~

brator's output is used to control (on/ ofl) a. constant current source using transistor T3. When lbe constant current sour" is activated (multivibrator•s output is low), capacitor C4 charges Unearty. And when it is inadivated, C4discharges th.rough

brator ia. this circuit .is designed with

resistor RS and diode D6.

transistors inste.ad of an oscillator IC

The voltage applied to R8 (from C4) determines the phase angle of Ute

drawn fmm this vollage. SO thecurre.n t

like NE555.

witb a step-down transformer (or even The circuit directly from. 230 v AC using a zeoer regulator)' w:ill make the ~ircuit bulky and ~itate adclilional oonnectin.g: The circuit ,diagram is shown in Fig. 1 wires. Such a circujl cannot be used as and the adual-si7.e PCB is shown in the direct replacement of a 2.-tenninal Fig. 2. The componemt side layout of mcdwlical svruch. The cil'.W.it ~

TmMistors Tl and TI work as a low-current mullivibrator having a frequency of abou[ 0.1 Hz. The multM-

the PCB is shown in Fig. 3.

2(Jt/·rvv .

"",.

I

Ft1$

l,6MI

trigg.cring pulse ~o the gate of the SCR. When this voltage is high, the phase angle will be low and the RMS output will be high. When it is [ow, 1he RMS output will be high. Wben it is low, the RMS output also will be low. So, when C4 charges gradually, lhc lig,hl outpl.rt of the lamp increases graduany. And A1t

UM

Cl •

1000ji 'Z5V

A 12

,100Q·

1f'ZN l't!O 471;1

0.1Hzrn

PARTS LIST

0

, &n1icomJ1"/()~s: , Tl-1'3 T4 DI , D2 -

0

!

03, 04, 06-mO" DS SCRl

OCSS8s.ilicon pnplnuistor

urr 2N2646 lNU48 diode

~111001

swltd1ing

-

l N4007 m:lificr diode 2-0V zeiter diode

-

4A, 400V SCR

Rcs-istor~ (all Jf4W±_ 5% ~arl> 1'2\1

Ri4 IOK

...............~,,,.,,.._,._IVll',.._+-1 1',~ ' +-+--H

............_ _ _ __ ____,.

~~o

~; R3(I 100K

6V

' CUI

..-+----' 10,.

fN

R37 100K

IC1 (!Mi)' = LM324 IC2 (a, b} LM1 458

=

R38

100KI

.....

~-----

C4 0.01p

.......IF---..._

020

470,. _.,.,.,_ _"""'l'M..,1-4 I :2V 4.7

Hg. Z ; Circuit dle9r•m for •~ttonlc lanpura.

il remains cur-of( due to the reverse bias. The ek.Clrolytie capacitor connected at the positive Une of this amplifier

serves as a storage of current for biasing. As the capacitor loses its charge, ~he outpu,t diminishes slowly. This- is

outputs oflhis IC are used and the fifth one is connected to lhe reset pin 1.5 to get a continuous operation. The clock pulses to this IC a~ven by a fifth oscillatorwired arolind one ofthe two op-

lhebasicprincipleofstriogsouodemu- amps of IC2(a). lation. This effect is impossible if analogue switches, viz, 4066. 4016 ere were used. Op-amps which have a co.o'lrol voltage pin> ·viz, MC3340 C3iJl be used instead of this type of switohe:s,. The po.sitive voltage for biasing the 86 l1911'1il•lQl[t1p;Jell!l!l~1!@111

IC2(a) and IC2~)arc in.eluded in a dual

switches is given from Lhe outputs, of de.cade counter IC 4017. The first four

op-amp LM1458. The powe.r audio amplifier is not so c:rilical. ·Any popular Circuit may be . used. Howev·er, an amplifier using 1

LM2002 iS suggested. n bas high output and zero hum pick-up.

A standard power supply ranging

The position of preset. VRS deter- from 6V to9V can be used with lhiscirmines the timing. A frequency of l Hz cuh. A suitable power supply circuit is is a marginal value. ! shown in Fig. S. 'Ille mixers1age is wi~around op.. The whole circuil sh:own in ·ig. 2 is amp IC2(b) whion functions as an ad.- intended ror automatic functioning. der arnpllfier. Its gain is fixed as 616. · When the power is applied, il works on

PUSH swrrCHE:s X:1 ~A,(: PAIUARV TO 7.Sl/.fHiSI/ tA SEC. TRAHSFOl'MEA

1G

SI

ON-OFF SWITCH

.--~~~~.----11~~0--0

•f!IV

fig. 1 : WtchM In manual model ov

fig> 5 : Qrcull dlagr•m

tor power eupply.

lhrougb

push

switches. In this case a cheaper op-

for this IC. An aluminiu11\ sheet having an area of 6x6 cm and 2mm thidcncss will serve the purpose.

amp, viz, 741 may

Tuning

be used as adder amplil'icri~tead

Audio oscillator 1 is considered as the

for this is shown in

~or acts~

of 1458. The circuit

Fig. 6. All the oomponelll.S a11 be housed jn a wooden loud-

speaker box. In the case of manual typt;

first string of tanpuca. The next 05Cillathe second string, and so on.

The first one should be 1iuocd ro get a

frequency of 384 Hz (middle G), the second and third to a frequency of 512 Hr (upper q. and the last one to plr duce a frequency of256 Hz (middle C). Tuning can be done using a frequency meter or directly with an organ or har-

all c-0mponen1s must be fitted into monium. a wooden housing A well filtered and regulated power Fl91. I : ·C hano- tor IMMllll opwellon (optlonal). in the shape of .supply is a must for the stable opera· its own. The circuit can.be modified to taopura.. 1be push swjtchcs are placed lion of this circuit. a manual type. For this, JO,. JC2 and at the tail end (Fig. 7). Note: The frequencies mentioned dioclcs Dl-D4 arc not nccesary. The Soekets must be used for the ICs. above are of pbysicaJ or natural noccs. positive tenninals of switches should LM2002 may be soldcr"Cd directly on The international SUlndard R!tch frcbe connected to pos.ilive supply Jine the.PCB. A good healSlnk is necessary quencies_are slighlly different.

Author's Comments l. How Cllll I change the scale of four no.t:es? Are VRJ to VR4 presets? 2. Can I use knob.type potentiometers for YR 1-VR4 :instead of presets? Shall it help for better tuning?

tor-emitter of BC548 transistor. Tool>-

0

tain a proper delay of the string effect.

lator circuit with NOR or NANO gates. · 2. lfdle output of 4017 lCs seem to be week 10 charge the capacitors. lhe .chargingcurre"it may be applied through

value of the capacitor should be around 100 µF. IC 4017 can't sink the required charging current reliabl.y.

4. Orte can also dispense with the adder opamp used in the design. But A Reader good results can be obtained U5ing a Bhubaneswar simple resistor adder_ l have following comments to make S. The output circuit around power · regarding the design and improvement amplifier I~ is quite critical. From my of this proje(:t: pointof view I findthatthepowersupply I . The oscillators are buUt al'Qund to the output IC must be through a sepaopamps. From my experience, these are - rate 'bus'. If not isolated. die notes of the not stable enough for a professional mu· ~verlapping strings wiU appearnoisy and sician to perform confidently. 'Sruthi' smudged. variations of even a few hertz can't be F'mally, to reduce the 'pluck sound', tolerated.1lie opamp oscillators are very a resistor of 1 or 2 .kilohms can be incorsensitive to fluctuations in die power porated in the emitters of the BCS47s. Phrabhakaran M. Nair supply. . 2. 'The range will not cover the miniTrichur mum of l .5 octaves required. Evensothe The author KA. saklltidharan replies: sweep will not be linear. The solution is Thanks toMfPrabhakaran for his sincere to build the oscillators with the good old and valuable suggestions for improving mck-steady IC 555. lhe performance ·Of my design. I would 3. The string effect is obtained by the like to express my comments as follows: charging and discharging of the 47µF l. In ~the requiRd frequency range, electrolytic capacitor across the collec~ (in octaves) is not obtained, try theoscil-

88l•a1a1ae]Q'lt'N§•''"'t'w1p

the uansistors Is suggested earlier.Mr. ·Prabhakaran suggests to invert the output of 4017s using NANO gates. The same effect can be obtained without i nvenieg if an npn transistor is used. 3. Elimination of mixer stage is not recommended in.view of die overlaping frequencies which mig,ht get distorted. 4. If any problem arises with the power amplifier, it can be minimised by increasing the value of decoupling cap.acitor C23. Otherwise, the main drouit may be connected to an external amplifier. Regarding the fLrs1. letter, the four oscillators may be tuned individually according to the musician's requirements, For ·this purpose presets VRl throug·h VR4 should be replaced by potentio~ meters alld fitted on the front pand.

SECTIONB: CIRCUIT IDEAS

Infrared Remote Control Switch Dtbyojyotl Banerjee

This

is a truly infmcd rays coo. trolled 1'mCbanical movemeols sbould not change lhe positi.ons of these leads. Fill ball 1X1rtioo of Ibis eocrosure with liquid metaW mercury. Memiry is available w ith college lab equipment dealers. Only a very small quantity ·Of mercury (one or two drops) is necessary. Then seal that end also. This.mercury swilcb is fixed in the inside wall of intercom ·cabinet at an

sound m.aybe produced. Sodoo'l try to decrease the value of this resistor. Use a red l.ED with 470..()hm series resistor f« oo/off:indicatioo. Doo'l press aill-bell switch at the time ofconversa· tion because call-bell sound is quite

loud. For operating this intercom just pick it U!.J) (from its horizontal rtSting position on table) and press call-bell swildl. On heariQg sound from the remote uoit, pick up the other unit. It's autc>-

malically switched on due to the action of .mer011Jry switch. After talking just keep it baCt homontally oo a table

1

where it would lie switched off. Readers should note that 8-pin as well as 16-pi 11 TDA2822 ICs are available in the market. They should use 8pin type wruch costs Rs 25 approx. If you want this intercom to be , mains operated, use a 3-volt regulated

power supply.

Programmable Digital Staircase Generator George Verghese T

he circuit shown here iS used to gives a 2--step wavefonn while pressing · lW and ar·e ronnected lo +5V via lk:

provide a staircase waveform of 2 to

S9 gives a 1Q.step staircase waveform.

resistors for greater n.oise immunity.

10 steps which is selected using, a pushbutton switch.. 1'5 time period and step size can b-e adjusted easily

The operation of the circuit can1be explained as follows.

accorcUng to one's needs..PressingSl

BCD encoder whose inputs arc active

Each input, i.e. pin l l to :Pin 5 (Al to A8) i:S fed to an 8-inpul NAND gate, further invett·ed to give ad AND rcalisalion..A9 (pin 10) ls connected as

The 7414'7 is a T'IL decimal-to-

,I,

... "" "" ...,

It- h

.... I

.. 11

liCt ..._

. _ _ , 1.11111

__.__.._..-lllHIC10

...

102 11911'1il•lQl[t1p;Jell!l!l~1!@111

••

. .... .

•tt' l--- - - - ' -..;ji.

-~

;n -:-~

Pl

h H1 ~ ~

Wlii 1..

Miii ti(

one input to a NAND gate and then inverted so tbat the whole combination b~ the effect of a 9-ioput AND gate. Thus wbeo any of the switches is pressed, pin 11 of lC3 (7400) goes low but otherwise it s tays high. The output of the NANO is further inverted tw.i ce so tbat. the original condition is obtained and fed to the clock input of the parallel shift register 7495 and to LOAD input oflhe74192 presettable BCDoountec, both of which are active low. The two inverters are used in series to provide a further propagation delay to the lowgoing pulse which ensures for the set up time of the 7495 (the mode control ofwbicb to pin 6 is held high for pai:allel operation) to latch.on coneclly to input. data. Thus when any of tbe switches is pressed, the oorrespooding BCD is loaded in the shift register and the 74192 counter via the load signal. As 74147 outputs are aetive lo·w, tbesehave to t>e inverted before ronn«t:ion tothe7495 inputs. Pins 15,10,1 and9of the74192, i.e.• data inputs, can also be grounded after disconnection from 7495 outputs. The control logic comists of four EXOR gates and a 4·input OR gate.. We require t:hat when the output of the 74192 counter reaches the selected BCD corresponding to decimal input, the counte.r be reset to count 0000. Thus eocb of the counter outputs, i.e., QA, QB Qc, Qo is compared wjth the 7495 output port and when the variables

are the same, all EXOR gates go low, and these being fed to the NOR gate provide a high level so that the CLEAR input of tbe 74192 to which tile output of NOR gate is oonoected is cleared and the count is 0000. The clock is supplied by a simple 555 in lhe ~able mode wbet>e frequency

asallswitcbesare disabled. Nowwbcn count is 0001, first switch in the 4066 is enabled and has r~istance of about SO. ohms so that now , Vx >C lOk

f=l.44/(RA+2RB)C can be varied to

and when count is 0010 second switch in 4066 is cnab led so that

suit the necessity of lime period of the

80+VR2+ VRH VR4+ !Ok

staircase.

The outputs of 74192 arc converted to equivalent hig_b voltages required for operation of the CMOS 4066 (quad

Vx>< lOk V2---~~~~~~~-

VR1+80+VRJ+VR.t+lOk Thus we see that corresponding to ooUector 1TL with pull-up resistor of each level we have a different voltage 5.6-k.ilohm. We cannot use ordinary level which gives rise to a staircase pull•up ~ that would damage lbe EXOR waveform. As potentiometers arc used gates. of IC7 as their inputs will be [or VRl. VR2, VR3 and VR4. we can the voltage levels for each ·pu Ued up to +Vx. when output is high. gel The 4066 acts as a simple DAC and independent slep. For taircascs with up to four steps, c.orresponding to the input we get the equivalent analogue voltage al pin 4. as the maximum count is 0011,VR3 Anot her feature of this circuit is that the and VR4may be kept at zero resistance. voltage of roaximwn step can be adjlEed For eight steps, the maximum count is to any value in the CMOS levels. bearing 011 1. VR4 may be kept at zero resi.5tance. jn mind that the maximurn current Thus we see that using this circuit we can .ha\le aoy number of steps selected through a switch :iS W mA. let us now see Lhc conversion to a from 2 to 10 with a pushbuHon switch .staircase waveform in. detail. Suppose whose time period is variable. AISO, the switch 3 is prcs.scd so tbecounler cou- voltage levels of each can be varied nts from 0000 to 0010 and lhen resets. correctly. Nowwbencounti 0000, voltageof Hence. we can easily design the pin 4 is calculated as circuit for any voltage level of the step we require by using potentiometers of l Vx.w l Ok kilohm for VRl to VR4. YR l+VR2+ VR.3+ VR4+1 Ok bilateral switcb) using the 7407 ·Open

Disco Light Without Transformer Shamsundar S. Chendake

D

isro light projects are not new for e1ectronic OObbyi so that it does not exceed lihe contact (tip) point ratings.

This relay makes (closes) and breaks (opens) tbc(X)Jltact points I and2, thus givin.g audible sound and visual ind icalion.

dependent set of contacts directly. This circuit functioned satiMadorily in an EPAX.system and soc.an be tried

with any similar system.

Twin floatin1 contact point of lhe

Emergency Light with Charger · Venugopal K.P.

T

be main feature of thts circuit is its low-cost. It can be assembled for just about Rs 120, excluding the cost of tbe baucry. In the given ciradt. when lhe AC

TU WI

mainssupply is present.the transfonn.e r Xl steps down the vollage through the relay connections. Diodes D1 and D2

2'2CM

rectify the voltage while capacitor Cl reduces the ripple ro provide DC , I vol tages . .The DC voltage charges the 1

battery lb.rough resistor R 1. The valu.eof R1should be so chosen as to give the dcsin:d current level. It is advisable to have two 1-obm resistor5 ·

X1 2!tfNN;m. TO rl--0-fN, 2A

SEC. nwt!FOAMER

in parallel, each rated at 1/2-wau.

When the AC majns supply fails, relay RLl gets energised through the ~T2, with the trami.stor working in forward bias. It thus coonects

tbC

Dl-05: INAOO? RL1 ; 100Q.4 POLE,2 WAY

C>W«lE ()VEA:FEl.AY Ra

isc z.sw

At O.!Q

1W

primary winding of transformer Xl to the tube ends. The secondary leads of Xl (including cxnue-1.ap) connect to the oscjllatiog transistor's base and collector accoroingly through its N/0 contacts. Transistor Tl wotkin,g as an

oscillator-cum-driver generates nuctu106llH311:Jt!Qll!1i:J•!li'.,1!@HI

aLing DC wh.ich is ste-pped up by &he tramformer. 1De high voltage thus

I

geoeratedumsb t\belightm. .~ sbOuld be used with transistor Tl.

Car Horn with Hindi Song Tunes · Pradeep G.

G

51

eneral circuits for musical car bOms .have appeared in. EFY. The cjrwit shown here g~rates tunes of 12 llindi songs. IC1 UM3481SA is used to deliver mndi musical tu~ while IC2, the popular IBASJO power amplifier, amplifies the music signals. Amplified music signals are heard from the loudspeaker. At 12 volts th~ circuit tan deliver4 watts outpuL The power supply can be decreased to 6 volts when the output powerwiUbecome r watt. Use suitable loudspeakers for different supply '

ON:.ot-f

S'WfTCHI ,-~~~~----1~~~~~--...~ty,t.~--.------1t@W

It .iS noteworthy that the acousrc

.circuit is set by YR 1. Diodes Dl and DS rem.aln conducting, and so the red 'NO'

mail indicator LED3 remains lit and

the pfe210/aural alarm tone oscillator remains deactivated.

perfectly suffice.

transponder is not a piezo buzzer but is

The circuit itself may be enclosed

a piezo speaker, w'hich is .also referretable mullivibrator.; OS.I and OS-II to yield pulses of 0.5 ms and 5 ms du.ration each as hown in lhe circuit. For this, the presets YR l aod VR2 may be adjusted around 2

long as the phase sequence is rol't'ed:, OS-III will constantly be retriggercd and the relay driven by it will remain ''On'. This relay should be used to

are a:xnmercially available in the market.

kilohm and pulse widths checked wi.t h

conirol a 3-phase maim contactor' that

Here is a new circuit idea and the underlying principle. The users. of 3~phasc AC moi:ors know that. ao jncorrect phase sequence ,can be oocrected simply by inteliChanging any two phase wires conn.ccled to the motor. This is possible because oftbe

an oscmoscope.

would feed the AC voltage to the motor or any other machinery. The 5-second Hme iaterval of OS·lll takes care o.f

through a device tl'lat would cut·offlhe

inher-ent 12()> phase difference between

any two phases (see figure). as a oonsequence of which any of the tbree combinations R Y B (for red, yellow and blue). YB R or BR Y yield 'the correct sequence. One can see that an incorrect pbasesequence, say, YR B can be restored to any of the abovemcntiooed ccmbinations l>y ex.changing any two colours (wires). Phase sequence diagram ~esmws how this can be done. Transistors Tl and T2 conduct as soon as the volmge 112 1191a1H•lQ•[t1p;1e11m~w•1•

The pulse widlh of IC 74123 is governed by the follow1ng formula: T =0.28 RC (l+0.7/R), where T, R and C are in milliseconds, :tilohms and microfarads respee1.ively.. OS-I triggers at the poshiv~going

edge and OS-II at the :negative-going edge. Their outputs are NANDed using diodes DS, 06 and transistor TI. If the phase sequence is correct, ~he pu1ses from OS-I will fall within the 5 ms window created by OS-U, and the collector of transistor T3 will go low for 0.5 ms every 20ms. If the phase sequence is incorrect the OS- l pulses will remaia oulside the window and the

collector of transistor T3 will remain oontinuously high. The output of tr~istor T3 is used

_

momen:lary interruptions or transients.. The +5 volt power supply is built us.ing the third phase. B. This arrangement ensures 1ha1 the supply to the motor rema_ins cul-off in the 00scooe of any of tbe three phases. Tue total cost of the components excJuding the, cos! of the 3-:phase

contactcr should be around Rs 200 or so. DI

Superb Equaliser V.A. Sarurkar

I

f you are in searcll of a oosteffoctivc graphic equaliser, your search may cod with this circuit. It gives boost/ cut of about :z:10 dB which is sufficient for oonnal fundiooillg. The ciro.dt OOS1S around Rs 40 including pocs for one

of which is wired as buffer amplifier to minimise the k>eding effeas. 1U soc:tiM must not be omitted as otherwise the output will go down drastically. The socood op-amp is wired as an active filter. ~. it is a modificatioo

The figure below shows tb.e circuit

of the popular Baxande.11 type tone control. The gaio. of the amplifier at a

diagram for one channel. Circuit fortbe

particular frequency depends upon the

cbaoocl.

constructed on a veroboard. Extrane care should be taken while soldering the IC as no PCB is being med. If you. are heavy-banded in soldering;. 1J1C an . IC socket. 1bc currcat consumption of tbe circuit is.about 30 mA, and..tbestandard 12V pow~r supply used in audio-decb can al.so be used for the equaliser.

A7 t!Jli( 4Qti;t

t12V

oc

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For sensing the voltage, the two comparators of IC SSS (trigger and threshold) are used.. We know that IC

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In this circuit. one main transformer (Xl) is used to givestabUised output of

AC supp,ly. Another transformer (X2) is used to give supply to the sensing

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comparator (pin 6 of IC) exoeedS 2/3 Vee This principle is used here to

To avoid flickering during. high 3.Sinccwecan•tgivebuckorboost circuit Sensing vohage is also taken from the transformer-XL · voltages transistor Tl is ~. It makes indication use a voltmeter ~ outFor low voltages ( 170V~200V), set tbe capacitor (C2) to disdwge to Ctttain put (if needed). 4. Use any type of ovcrvolLage wtVR2 to switctl on tbe triac, and for lligh value in the absenoe of seming voltage. · off circuit for the voltages above 270V VOllagtS (100V·27-0V) set VR1 lO ~ , Settings .o fVR:i and VR2 is to be done (above this voltage it is gives flickering •,off' the triac. Wilm tbe triac is off, · only with load. the output will be zero. At the same For aisfadory operalioo please note effect). 5. Keep die control citcuit in plastic tim~ iai absellCle of the seoSing voltage, · the follow.ing points: l.Cooneoteartbpointonlyaftcrthe box because it is coonected to I.he IC SSS giv·es high output. as its pin 2 goes to ground level. Alternate opera- anode of D3. supply line. lion of 'on' and 'off' main.t ains a 2. Dot on the transformer denotes 6. Output voltage settings are lo be steady voltage. ' that the end should be start end. done only with load~

Dual Tone Siren PradeepG.

This

ciraiit generates a dual tone soood. ICl generates pos1tive output

pulses at an interval or about 1 seco:ad. Tramistors T3 and T4 frm the popular complimentary pai.r AF oscillator. If ICl ~ not generate positive pulses, only R5 is ronoected ro the base of T2. ha ASUl.t the O'iCillat -

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lnterco,m.Cum FMTransmitter

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gencratort amplifier alld FM lranSmitter.

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condenser mic (in speak mode) ~s also fed to tbesameampUfier.Resistor ~7 js used for feedback. The FM transm 1ncr

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copper wire 0113mm wide aircore. When swilch Sl is in 'call' positfon, the speak.er in ttae other room stans

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In the ~m pUfier circuit. JC 1(UM66) is used to gcne:rale 64 music.al notes. The IC'soutpurt "from pin l isamplific:O by transistor Tl. IC2 (741) and a pafrof

tram;istors (f2 and T3) are used to amplify the signal. The signal from

Readers, Comments

0..01,. .

circuit is built around lrnnsis1or T4 (BF494). The oulputof1'4 is frequency modulated with lhc help or a tank cirwil comprising capacitors C9 and CW in parallel wi.lh Lt. ·Coil Lt is made by gjvjng 3.S turns of28SWG enamelled

beeping. Toopcral·e the FM transmiucc, Sl should be kept in •speak' positi.on and S2 in ·~ran~mit' position. The fM receiver opicralcs at 97 MUz.

. ·INTEACOM SEf 1

I. Can one use a 9V cell for I.he circ\Jil? 2. 'J:o which part. of the circuit the l.oudspeaker LS2 is co be connected? 3. ls it possible t.o · make a..two-way intercom using lhe same circuit twice? . d) What is the ran.g e of operation?

P:N. Rafendra Kumar 2. The loudspeaker can be conne(:ted the figure here. 4, 1be system can be operated within as shown here. Tht au1hor, M.r G.H. Lodhi', rtplieJ; few meters but with some modificatiom. 3. It. i,s possible to make a two-way inL Yes, a 9V ceH .is recommended for ' tcr