Table Of ContentE A d d - o n
P r o j e c t s f o r
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C o m m o d 6 4 ,
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a a c
V I C - 2 0 , M i c r o :
o r n l e c t r o n
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OWEN BISHOP
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Easy Add-on Projects for
Commodore 64, VIC-20, BBC Micro
and Acorn Electron
OTHER TITLES BY THE SAME AUTHOR
BP73 Remote Control Pr-ojecte
BPS2 Electronic Projects Using Solar Cella
BPI04 Electronic Science Projects
BP124 Euy Add-on Projects (or Spectrum, ZX81 & Ace
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OTHER BOOKS OF INTEREST
BP130 Micro Interfacing Circuits - Book 1
SPl3t Micro Interfacing Cil'Cuite - Book 2
8Pl3S Secreta of the Commodore 64
BP139 An Introduction to Programming the BBC Model B Micro
BP142 An Introduction to Programming the Acorn Electron
BP147 An Introduction to 6502 Machine Code
Easy Add-on Projects for
Commodore 64, VIC-20, BBC Micro
and Acorn Electron
by
Owen Bishop
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BERNARD BABANI (publishing) LTD
THE GRAMPIANS
SHEPHERDS BUSH ROAD
LONDON W6 7NF
ENGLAND
PLEASE NOTE
Although every care has been laken with the production of this book
to ensure that any projecta. designs, modifications and/or program!
etc. contained herein, operate in a corrrect and Safe manner and alsel
th'at any component.ll specified are nonnally available in Great
Britain, the PubliaheNi do not accept respofUlibility in any way for
the failure, including fault in design. of any project, design, modifi
cation or program to work correctly or to cause damage to any other
equipment that it may be connected to or used in conjunction with,
or in respect of any other damage or injury that may be 80 caused,
nor do the Publishen accept responsibility in any way for the failure
to obtain specified component.&.
Notice is also given that if equipment that is still under warranty
is modified in any way or used or connected with home-built
equi~~
menl then that warranty may be void.
All the projects in this book have been designed and tested by the
Author using models of the various microcomputers that were avail·
able i.n Great Britain at the time of writing. The Author and Pub
lishers accept no responsibility for failure of a project to operate or
any damage that may be caused, should the manufacturers of the
80
microcomputers radically change the of their machines
s~ification
in the ruture or ror a particular overseas market.
©
1985 BERNARD BABANI (publishing) LTD
First Published - March 1985
British Library Cataloguing in Publication Data
Bishop Owen
Easy add--on projects for Commodore 64, VIC·2Q,
BBC Micro and Acorn Electron.
l. Computer interfaces
2. Microprocessors
J. Title
001.64'04 TK7887.5
ISBN 0 85934 109 7
Printed and Bound in Great Britain by Cox & Wyman Ltd, Reading
Contents
Page
INTRODUCTION I
••••••••••••••••••••••••••.•.•.•..•.•.•.• •••••••••••••••••••••••••••••
........................... .
Interfacing to Microcomputers ." , I
Logic Levels in Computers 2
•••••••••••••••••••••••••••••••••••••••••••••••
User Port 2
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
Decoder ............................................................................. . 6
Programming Sum.maries ............................................... . 15
Project I: PULSE DETECTOR 19
••••••••••••••••••••••••••••••••••••••
How It Works 19
••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
Building It ........................................................................ . 21
Using It ............................................................................. . 21
Detecting "'High Pulse" ................................................. . 23
8
Project2: PICTURE OIGITISER 24
••••••••••••••••••••••••••••••••••
How It Works 24
••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
Building It ........................................................................ . 29
.......................................................................
Final Check 33
....................................................................
Test Program 33
.. ..
Programming ............................. .............................. . 35
" , ,
..............................................
Project 3: FIVE·KEY PAD 41
.................................................................... 43
HowIt Works
Building It ........................................................................ . 45
Testing .............................................................................. 46
•
...............................
Project 4: MODEL CONTROLLER 50
....................................................................
How It Works 50
Buildi.ng It ........................................................................ . 55
Programming ................................................................... . 57
ProjectS: BLEEPER ........................................................ 62
How It Works .................................................................... 62
..................................... .................................. .
Building It 64
,
Programming ................................................................... . 67
Page
...........................................
Project6, LAMP FLASHER 68
·. ..................................................................
How It Works 68
...................................................................
Building It ..... . 71
Programming ................................................................... . 71
.....................................................
Project 7, LIGHT PEN 73
·. ..................................................................
How It Works 73
.
.. .. .. . .
Building It . . .. . . . ..•...................................................... 74
Progrlllllllli.ng ................................................................... . 81
Project8, MAGNETIC CATCH ..................................... 85
·. ................................................................. .
How It Works 85
Building It ........................................................................ . 88
............ ............................................. . .......... 92
~~IlJl1ll1ling
,
Project 9, LAP SENSOR 94
.................................................
·. ................................................................. .
How It Works 94
Building It ................ .........................................................
97
................................................................... . 98
~~llrlll1li.ng
...........................................
Project 10, PHOTO· FLASH 101
·. ................................................................. .
How It Works 102
)f>l"()irI"llIllrlling ................................................................... . lOS
.....................................
Project II, GAMES CONTROL 109
·. ..................................................................
How It Works 109
Building It .......... ............................................................... 112
................................................................... . 114
)f>ro~arllrlling
.......................................
Project 12, RAIN DETECTOR 116
How It Works .................................................. .................. 116
Building It ........................................................................ . 117
................................................................... . 118
~irI"IlIllJ1ling
Project 13, WEATHERCOCK 120
........................................
How It Works ................................................. 120
• ••••••••••••••••••
Buildi ng the Vane ............................................................ . 123
Building the Circuit .................. ....... ................................ . 124
................................................................... . 125
Jl1r()~llrJlIlling
Page
Project 14, ANEMOMETER ........................................... 127
How It Works ...... .............................................................. 128
Building It ......................................................................... 130
Program.m.ing ...................... .............................................. 132
Project 15, THERMOMETER ............. ........................... 135
How It Works .................................................................... 135
Building It ....... ... ............................................................... 138
Calibration and Programming ....................................: . .. 139
Project 16, BAROMETER .............................................. 143
HowIt Works ..................................................................... 143
Building It ......................................................................... 147
Programming ..................... ... ............................................ 150
Project 17, SUNSHINE RECORDER ........................... 155
How It Works .................................................................... 155
Building lt ......................................................................... 158
Appendix k THE DECODER ........................................ 165
How It Works .................................................................... 165
Power .................................................................. 169
~uJ'J'lies
Building the Decoder ............................ ............................ 171
.A5sembling the P.C.B. ...................................................... 171
IC Sockets ................. ......................................................... 177
Fitting the Case ................................................................ 177
Decoder/ComJ'uter 1nterconnectors ................................ 178
Testing .............................................................................. 183
Appendix B, DECODER WITH AN INTERFACE FOR
THE ACORN ELECTRON ........ .............. 165
How It Works .................................................................... 185
Testing the Elect) on Version of the Decoder ................... 186
Programming .................................................................... 187
Appendix C, SUPPLIERS OF P.C.B .• AND KITS ..... 188
AppendixTh PIN ANDLEAD·OUTDETAIIS ........... 190
Introduction
Interlacin g to Micr ocomputer s
This book describes how to build circuits which
el~lronic
you can attach to your VIC·20, Commodore 64, Acorn
Electron or BBC Microcomputer. All the devices have been
tested, most of them with most of the machines. Owners of
the BBC Microcomputer Model A should note that. they will
need the User Port upgrade for their machine to allow it to
operate with the devices in this book. For Project 11 they will
need the Analogue Port upgrade too. All the devices have
been tested with all of these computers.
All the projects are simple and inexpensive ones, requir
ing only a few transistors or integrated circuits. The inte
grated circuits 8.re oflhe less expensive kind. The wiring re
quired for each circuit has been kept to a minimum, an unus
ual feature for a book oflhis kind, for microprocessor projects
tend to need rather more wires than projects of other kinds.
The result of this simplified approach used here is that all
the projects can be built easily and cheaply, even by a rela·
tive beginner. Once built, they are simple to operate. Writ
ing programs to control them need not be complicated. Each
project includes a simple program or two to get you started.
Of course, those readers who are more expert at programm·
ing can have lot of fun in writing elaborate programs based
8
on these projects. but the beginner can start with the short
program and perhaps add extra fea tures later.
The circuit designs apply equally well to the VIC·20. the
Commodore 64. the Acorn Electron and the BBC Microcom
puter. If you have a VIC·20 now, for example. and later
change to one of the other computers, the projects can be
operated from your new computer without having to alter
them. If you have previously built similar projects for the
ZX81 . Spectrum, or Jupiter Ace, as described in book num·
ber BP124 . Easy Add-on Projects for Spectrum, ZX81 and
1
