Maplin auto electronics projects P1

Maplin auto electronics projects

B u t t e r w o r t h - H e i n e m a n n and Maplin E l e c t r o n i c s P i c Books in the s e r i e s are p r a c t i c a l guides which offer elec-tronic c o n s t r u c t o r s and s t u d e n t s c l e a r introductions to key t o p i c s Each b o o k is written and compiled by a lead-ing e l e c t r o n i c s author

Other b o o k s published in the Maplin s e r i e s include: Computer Interfacing

Logic Design

Music Projects

Starting Electronics

Audio IC Projects

Video and TV Projects

Test Gear & Measurement

Integrated Circuit Projects

Home Security Projects

The Maplin Approach

to Professional Audio

Graham Dixey 0 7506 2123 0 Mike Wharton 0 7506 2122 2

R A Penfold 0 7506 2119 2 Keith Brindley 0 7506 2053 6 Maplin 0 7506 2121 4 Maplin 0 7506 2297 0 Danny Stewart 0 7506 2601 1 Maplin 0 7506 2578 3 Maplin 0 7506 2603 8

T.A.Wilkinson 0 7506 2120 6

Auto

Electronics Projects

U N E W N E S

- ^ J j A member of the Reed Elsevier group

OXFORD LONDON BOSTON

MUNICH NEW DELHI SINGAPORE SYDNEY

TOKYO TORONTO WELLINGTON

© 1995 Maplin Electronics Pic

All rights reserved No part of this publication may be

reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of

a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England W1P 9HE Applica- tions for the copyright holder's written permission to

reproduce any part of this publication should be addressed to the publishers

The publisher, copyright holder and author have taken all reasonable care to prevent injury, loss or damage of any kind being caused by any matter published in this book Save insofar as prohibited by English law, liability of every kind including negligence is disclaimed as regards any person in respect thereof

British Library Cataloguing in Publication Data

A catalogue record for this book is available from the

British Library

ISBN 0 7506 2296 2

Library of Congress Cataloguing in Publication Data

A catalogue record for this book is available from the

Library of Congress

Edited by Co-publications, Loughborough

£ ^ Typeset and produced by Sylvester North, Sunderland all part of The Sylvester Press ^

Printed in G r e a t Britain by Clays L t d , St Ives pic

This book is a collection of articles and p r o j e c t s previously

published in Electronics — The Maplin Magazine

Each p r o j e c t is s e l e c t e d for publication b e c a u s e of its special features, b e c a u s e it is unusual, b e c a u s e it is electronically clever, or simply b e c a u s e we think r e a d e r s will be interested

in it Some of the devices used a r e fairly specific in function —

in o t h e r words, the circuit is designed and built for one

pur-p o s e alone Others, on the o t h e r hand, a r e not spur-pecific at all, and can be used in a number of applications

This is just one of the Maplin series of books published by Newnes books covering all a s p e c t s of computing and electron- ics Others in the series a r e available from all good bookshops Maplin E l e c t r o n i c s Pic supplies a wide range of e l e c t r o n i c s

c o m p o n e n t s and o t h e r p r o d u c t s to private individuals and trade c u s t o m e r s Telephone: ( 0 1 7 0 2 ) 552911 or write to Maplin

E l e c t r o n i c s , PO Box 3, Rayleigh, E s s e x SS6 8LR, for further details of p r o d u c t c a t a l o g u e and locations of regional s t o r e s

The modern m o t o r v e h i c l e is a precision-built

highly-t u n e d m a c h i n e High s p e e d p e r f o r m a n c e , low fuel

c o n s u m p t i o n and quiet smooth-running engine all rely

on efficient ignition, b a t t e r y charging and general trical s y s t e m s throughout the c a r

elec-The e l e c t r i c a l s y s t e m is very c o m p l e x One only has to look behind a d a s h b o a r d to s e e t h e h u n d r e d s of wires of all sizes and c o l o u r s , i n t e r c o n n e c t i n g the instruments, high voltage and high c u r r e n t c i r c u i t s Also, t h e electri-cal s y s t e m is very prone to breakdown, w h e t h e r this is a blown lamp bulb, a faulty dynamo or badly adjusted con-

t a c t b r e a k e r points

No two models of c a r s have identical e l e c t r i c a l c i r c u i t s

T h e e l e c t r i c a l c i r c u i t s are, however, similar and fall into

c a t e g o r i e s s u c h as c o n v e n t i o n a l ignition or e l e c t r i c a l ignition, dynamo or alternator, positive or negative earth

This c h a p t e r d e s c r i b e s the b a s i c s y s t e m s : it is left to the individual c a r owner to interpret the d e s c r i p t i o n s and diagrams to suit their particular v e h i c l e

One word of warning Car e l e c t r i c c i r c u i t s can c a u s e damage to either the c a r or to the user if t a m p e r e d with For i n s t a n c e a short circuit a c r o s s the b a t t e r y can gen-

e r a t e hundreds of a m p e r e s and a lot of heat, even a fire: the ignition circuit g e n e r a t e s very high voltages indeed: tampering with the instrument c i r c u i t s , can c a u s e mis-leading readings and a p o s s i b l e safety hazard to t h e driver B e f o r e e m b a r k i n g on any c h a n g e s to t h e c a r

e l e c t r i c s , make every effort to understand how the cuit works In this way fault finding should be greatly simplified

cir-The ignition circuit

T h e p u r p o s e of the ignition circuit (Figure 1.1) is to ply the high voltage required to o p e r a t e the spark plugs

sup-in the c o r r e c t s e q u e n c e and so ignite the air/petrol ture in e a c h cylinder T h e explosions generated push the pistons and so turn the engine, causing motion T h e cir-cuit c o m p r i s e s t h e c a r b a t t e r y , an ignition c o i l , t h e distributor and four (or s i x ) spark plugs T h e principle

mix-of operation is d e s c r i b e d later

Figure 1.1 The ignition c i r c u i t

Battery charging

All e l e c t r i c a l s y s t e m s draw their power from the 12 volt

b a t t e r y (Figure 1.2) If the b a t t e r y was not continually

c h a r g e d it would b e c o m e e x h a u s t e d very quickly, ticularly if t h e lights, wipers and s t a r t e r m o t o r were in

par-c o n s t a n t use T h e turning of t h e engine par-c h a r g e s the tery by c o n n e c t i n g it to a dynamo, via t h e fan belt A

bat-pulley network at the front of the engine c o n s t a n t l y turns the dynamo which g e n e r a t e s enough power to c h a r g e up the battery A control b o x c o n t r o l s the charging rate and informs the driver via the ignition light if the b a t t e r y is not charging Some c a r s use an a l t e r n a t o r in p r e f e r e n c e

to a dynamo T h e s e are more efficient but g e n e r a t e a.c rather than d.c and so require rectification of the a.c output B a t t e r y charging is d e s c r i b e d later

Figure 1.2 The battery charging circuit

Lighting

T h e lighting c i r c u i t s are t h e simplest of all t h e s e , prising a simple c o n n e c t i o n of t h e 12 volt lamp to the

com-b a t t e r y via t h e instrument panel s w i t c h e s (Figure 1.3)

T h e s e c i r c u i t s are c o m p l e t e l y independent of t h e tion and charging c i r c u i t s , t h e o n e c o n n e c t i o n to e a c h lamp being taken via a single wire and r e s p e c t i v e switch

ignito t h e battery; the o t h e r c o n n e c t i o n u s e s t h e c a r c h a s sis T h e lighting c i r c u i t s are d e s c r i b e d in m o r e detail later

-Figure 1.3 The lighting c i r c u i t

Figure 1 4 The indicator and accessories circuit

Indicators and accessories

Contained within this circuit is the s t a r t e r m o t o r which draws hundreds of a m p e r e s from the b a t t e r y to turn the engine until it fires (Figure 1.4) Heavy duty c a b l e and a heavy duty solenoid c a r r y out this operation, which is prone to trouble for various r e a s o n s Also t h e r e is the fuel pump which is a small solenoid o p e r a t e d device to

pump petrol from t h e tank to the c a r b u r e t t o r , the

indi-c a t o r light indi-cirindi-cuitry with hazard warning lights, the radio and c a s s e t t e player c i r c u i t s , the h e a t e r and wiper mo-

t o r s , horns, instrument gauges, and h e a t e d rear s c r e e n

T h e s e c i r c u i t s are relatively simple and are d e s c r i b e d

t o g e t h e r with fault-finding t e c h n i q u e s later

Wiring diagram

Car wiring diagrams are often very difficult to read and interpret T h e r e a s o n for this is that, in a modern c a r with a large number of instruments, lights, a c c e s s o r i e s and m o t o r s , all are to b e i n t e r c o n n e c t e d on one c o m p r e -hensive diagram Fuses and switches must also be shown,

t o g e t h e r with t h e c o l o u r s of t h e wires and c a b l e s ; many manufacturers use an international colour c o d e for easier identification of the r e s p e c t i v e circuit c a b l e s

S o m e of the more popular s y m b o l s used in c a r wiring diagrams are illustrated in Figure 1.5 T h e c a b l e s are of-

t e n c o d e d a n d c o l o u r e d for i d e n t i f i c a t i o n a n d a

s h o r t h a n d m e t h o d of simplifying t h e d i a g r a m often groups all in one bundle (called a cable-form) as a single line T o t r a c e the start and finish of one c a b l e involves almost m i c r o s c o p i c analysis of all c o n n e c t i o n s , s e a r c h -ing for the required c o d e and c o l o u r

E l e c t r o n i c d e v i c e s s u c h as e l e c t r o n i c ignition or t h e

d a s h b o a r d m i c r o p r o c e s s o r are shown as simple b l o c k s Fault finding within t h e s e d e v i c e s must be left to t h e

s p e c i a l i s t dealer

The engine

The most c o m m o n small to medium c a r engine is the

4-c y l i n d e r p e t r o l i n t e r n a l 4-c o m b u s t i o n e n g i n e M o r e powerful engines have six cylinders, s o m e have eight;

m o t o r c y c l e s and m o p e d s have one or two T h e ment of cylinders varies, s o m e being overhead cam shaft,

arrange-s o m e p u arrange-s h r o d and r o c k e r , and o t h e r arrange-s with c y l i n d e r arrange-s

aligned in the s h a p e of a V

This brief description of the 4-cylinder engine, highlights

t h e i m p o r t a n c e of a c c u r a t e timing s o as to m a x i m i s e power and p e r f o r m a n c e Figure 1.6 shows the arrange-

Compression Power Exhaust Induction

Induction Compression Power Exhaust

Figure 1.6 4 - c y l i n d e r and 6-cylinder engines

Figure 1.7 The four stages of combustion

• induction — the petrol/air mixture is sucked into the cylinder,

• c o m p r e s s i o n — the piston c o m p r e s s e s the mixture,

• power — the spark plug ignites the mixture ing an explosion which p u s h e s the piston down,

caus-• exhaust — the piston p u s h e s the burnt gases out

of the cylinder

T h e four cylinders o p e r a t e in s e r i e s s o that, at any one time, one is being powered T h e crank shaft positions the pistons in the c o r r e c t s e q u e n c e , two c o m p l e t e revo-lutions (720°) comprising the c o m p l e t e four-stroke cycle

T h e e l e c t r i c a l c i r c u i t s have the j o b of supplying e a c h spark plug with a high voltage pulse to power the piston

in the c o r r e c t s e q u e n c e , and at the time when the piston

is at the top of its s t r o k e (top dead c e n t r e ) T h e tor e n s u r e s that the pulses travel in s e q u e n c e to the four spark plugs and, at the s a m e time, time the pulse to top dead c e n t r e

distribu-Basic ignition

T h e main c o m p o n e n t s of the ignition circuit are the

igni-t i o n c o i l — a c y l i n d r i c a l igni-t r a n s f o r m e r w i igni-t h igni-t w o

c o n n e c t i o n s SW and CB and a high tension c a b l e going

to the distributor ( s e e Figure 1.8) — and t h e distributor

— a m e c h a n i c a l d e v i c e coupled to the engine via skew gears This a c t s as a four-way switch to route the high tension to the spark plugs, and as a m e a n s of generating the high tension voltage

Figure 1.8 Basic high voltage generating circuit

Figure 1.8 shows the b a s i c high voltage generating cuit T h e operation is as follows, assuming the c o n t a c t

cir-b r e a k e r points are initially c l o s e d ( s e e Figure 1.10):

• the piston in one cylinder ( s a y number 1) rises to top dead c e n t r e , c o m p r e s s i n g the petrol/air mixture,

• the rotor arm in the distributor cap points to the

a p p r o p r i a t e high t e n s i o n c o n n e c t i o n t o s p a r k plug number 1 and,

• the c o n t a c t b r e a k e r points open,

• the magnetic field in the primary of the ignition coil (Figure 1.9) quickly c o l l a p s e s T h e t u r n s ratio of the transformer of about 10,000 to 1 transforms this collapse into a voltage of about 20,000 volts a c r o s s the s e c o n d -ary,

• the high tension pulse ignites the petrol/air ture in cylinder 1 causing the engine to r o t a t e ,

mix-• the distributor shaft r o t a t e s to again c l o s e the

is critical t o g e t h e r with the gap width T h e points, after

a period of wear, tend to c o r r o d e and pitting o c c u r s ; a deposit which builds up and r e d u c e s t h e effective gap

T h e gap is usually about 25 t h o u s a n d s of an inch wide,

o p e n s and c l o s e s s o m e ten million t i m e s e v e r y 1000 miles One o t h e r adjustment to optimise the timing is the dwell angle This is t h e number of d e g r e e s that the points remain c l o s e d ; refer to the maker's manual for

t h e r e c o m m e n d e d value

Ignition timing is carried out in the following s e q u e n c e :

• c h o o s e cylinder number 1 — c o n s u l t the manual,

Φ l o c a t e the timing marks on the fan belt pulley ( s e e Figure 1.13),

• turn the engine crank shaft until the marks align at top dead c e n t r e ( t d c ) T h e engine can be turned by placing the c a r on level ground, take out all the spark plugs, place in top gear, r e l e a s e the b r a k e s and move the c a r to and fro,

• e n s u r e that the distributor rotor arm points to the high tension lead to cylinder number 1 If not, turn the engine through a further 360°,

• c o n n e c t a 12 V lamp b e t w e e n the c o n t a c t b r e a k e r spring ( s e e point X in Figure 1.12) and a good earth point,

• r o t a t e the engine by about 20°, then inch it slowly backwards until t h e lamp just lights,

• if t h e t.d.c reading is i n c o r r e c t , align t h e t.d.c mark, then l o o s e n the distributor clamping nut (point Y

in Figure 1.11) and turn the entire distributor wise until the light just goes out Then turn c l o c k w i s e until it just lights Clamp the nut,

anticlock-• c h e c k the t.d.c setting o n c e again,

• r e p l a c e the plugs, put on the b r a k e s and take out

of gear! A faster m e t h o d u s e s a s t r o b o s c o p e with the engine running, a Xenon tube flashing as the points open and c l o s e

Electronic timing

T h e s y s t e m s o far d e s c r i b e d s o m e t i m e s fails b e c a u s e of pitting of the points and wear and tear of the moving parts of the distributor Two types of e l e c t r o n i c s y s t e m are found:

• t r a n s i s t o r i s e d ignition or c a p a c i t o r d i s c h a r g e tion — s e e Figure 1.14 and,

igni-• c o n t a c t l e s s ( o p t i c a l or m a g n e t i c ) ignition