Your Spectrum
Issue 5, July 1984 - Book Reviews
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Software might be the success story of the 'eighties, but without the hardware boffins just think where microcomputing would be. John Flenley, logic and software designer, examines the bookshelves to see just how much encouragement there is for the potential hardware freak.
Sir Clive Sinclair has a lot to answer for. Apart from bringing the world digital watches and introducing a new word into the English language - 'computer window' - he's also been indirectly responsible for the publication of literally thousands of different books and magazines, examining every possible aspect of ZX computers. Someone rumoured that half the trees in the Amazon rain forests disappeared into paper mills the day the QL was announced - and I believe it!
But let's look at this paper mountain again. I said earlier, that every aspect of ZX computing had been covered, but ... perhaps that's not quite true, for there does seem a distinct lack of books on the subject of DIY computing. The increase in availability of sophisticated hardware has not been matched (apparently) by an equivalent increase in understanding of how that hardware works. Arthur C Clarke once said, "Any sufficiently advanced technology is indistinguishable from magic", and I guess that's how a lot of people view computers - as magic boxes.
So, at the behest of our trusting editor, I decided to take a look at what books are available on the subject.


To kick off, there's Adrian Dickens' Spectrum Hardware Manual published by the prolific Melbourne House. At £5.95 it has to be one of the best. The book itself is printed on good quality paper and, even better, I only found two printing errors - both of which were obvious and unlikely to mislead. Mr Dickens has a very easy to understand style of writing and also uses illustrations to good effect where needed. The book covers every aspect of Spectrum hardware in minute detail - what it does and how it does it. Circuit diagrams of the part under discussion are included in each chapter.
Both issue 1 and 2 machines are discussed and illustrated, and I imagine that the Mark 3 was still undergoing frantic development when this book was being written; no matter, it's just as valid for issue 3. Another chapter is devoted to fine tuning of the video circuit, something that every Spectrum probably needs. This should enable you to get rid of those stubborn colour tinges
in your whites, or those striations around the edges of characters. You're also provided with a circuit diagram of a 32K upgrade, which should provide you with enough information should you decide to build your own.
Other projects to be found at the end of the book include the addition of a PIO chip, a large keyboard, a Spectrum- compatible joystick interface and an eight channel analogue- to- digital convertor. These are all well presented and ought not give any problems to the soldering iron wielder. You'll also find a complete parts list, a chapter on fault diagnosis and a full logic circuit of the Spectrum.


The second tome I examined was Easy Add-on Projects For Spectrum, ZX81 And Ace by Owen Bishop. While not discussing the hardware of the Spectrum, it does outline several different build- it- yourself projects. All require you to build a separate address decoder to the circuit design given in the book. And it's here that I find my first criticism. If you're trying to teach a
beginner about a subject, surely it's essential that you explain not only how you do something, but also why.
The address decoder is the basic building block of any hardware project, and the choice of address used is very important if you wish to avoid interfering with other devices attached to the micro. This is especially true for a machine like the Spectrum, where the misuse of an address line can cause havoc. The book explains very well how to build the decoder - no complaints there - but it doesn't give any insight into the way the author arrived at the choice of address lines. And it seemed to me that the design of the decoder itself was perhaps a little too complex, considering the fairly simple job it had to do.
Anyway, on to the actual projects. From the way the author makes good use of household items to build the various bits and pieces I get the impression that someone must be an avid fan of Blue Peter. The first few projects were interesting - a pulse detector (a simple device that you would find in any hobbyist kit and a good one for starting with), a small keypad, a bleeper, a model controller, a crude picture digitiser

and a light pen - but as I got further into the book, I somehow felt they began to get, how can I put it, a little silly. It was as if the author had got so fed up with people saying, "Nice micro you've got there,but what does it actually do?", that he'd written everything he could possibly think of to build. And around this point, he seems to run out of good ideas.
The magnetic catch (that could be used to let the cat out in the morning) and the lap sensor for Scalextric cars raised a smile, the 'Heath Robinson' barometer and anemometer caused a chuckle or two - and by the time I reached the sunshine recorder and rain detector, I was rolling in the aisles. Next time someone asks you what your micro can do, tell them that with the addition of some extra hardware and a few yards of wire trailing across the garden, it can convey the news that it's raining ... then see if they're convinced of the usefulness of a micro. Honestly, I think that the last few projects could be classified under 'Inane uses of high technology', however much they may inject a spark of humour into the book.
To be fair to the author though, all the projects are well presented, with circuit diagrams and drawings that help with the construction of associated hardware. But although enough information is given for the beginner to build a project, it would have been helpful to have included hints on what to do if the thing doesn't work when completed.


The third publication I looked at was Stephen Adams' 20 Simple Electronic Projects For The ZX81 & Spectrum. Here, all the projects are interesting and have the added advantage of being ones that the hobbyist might actually want to build (maybe I ought to have a go at that rain detector!). Full marks to Mr Adams for his inclusion of a section on the dos and don'ts of soldering; 98 per cent of all damage caused to ICs can be attributed to faulty soldering technique and it's good to find an author stressing the point.
He goes into details on addressing, explaining what lines are safe to use and why. And each project is well covered, with adequate circuit diagrams and explanations, plus a photograph of the finished article - giving you a reasonable idea of what you're supposed to end up with. Particular projects included are: a tape recorder control; an A/D convertor; a light pen; a shift lock for keyboards; and a very useful device for turning lights on and off around the house while you're out (see, all you doubters out there ... that's what a micro can do!). Then there's the mandatory burglar alarm; although no details are given on how to connect it up to a siren or alarm and, somehow, I
don't see burglars fleeing in panic at the sound of the Spectrum BEEP!
There are also details on a digital voltmeter, even if the range provided - between -5v and +3.5v - gives it a rather limited use. A logic probe and standby power supply round up a goodly selection of projects. Overall, it seems an excellent book for both the beginner and the slightly more advanced hobbyist.


I'm not really sure what the next book is all about. Sinclair Spectrum & ZX81 Add-ons by Natasha Graham and Michael Roberts should perhaps be retitled The Best Of Thurnall Electronics Instruction Leaflets, because that seems to be the amount of it. The 'projects' included are actually programs that you can run only by using one or more (usually more) add-on units manufactured by a Manchester-based company called Thurnall Electronics. It says at the beginning that details are given on how to build the units yourself, but I'd suggest that no beginner could build anything from such sketchy information. OK, so let's assume that you are fairly knowledgeable on the subject of electronics and can actually build one of these units. What delights await you?
Well, how about the 'Disco light show', that turns eight LEDs on and off in random patterns? No? Well, then there's the visual metronome where four LEDs are turned on and off? Oh dear, you're still not impressed. Sadly, nothing much changes during the rest of the book, just chapter after chapter offering program listings enabling you to do similarly astounding things with a variety of Thurnall units.
The advertising blurb on the back cover says, "This book shows you all you need to know as an introduction to hardware design and microcomputer interfacing" - it must be talking about another publication! At £5.95, I cannot really see it making any kind of significant impact on DIY computing.
Next in the queue came Interfacing Microcomputers To The Real World by Murray Sargent III and Richard L Shoemaker (what makes you think they're American?). A real epic of nearly 300 pages, it's packed with high- brow electronics and computer-based witticisms along the lines of "the trouble with computers is that they do what you tell them to, and not what you want them to do". Really, it's an excellent book, though not one for the beginner. It covers everything you could possibly want to know about digital logic and has extensive sections on the Z80 chip - including programming it - video circuitry, raster scanning, disk operating systems, and so on. If you already know the basics and are thirsting for some
advanced circuitry, this is definitely the book for you.


Finally, for those heavily into electronics there's An Introduction To Digital Logic by A Potton - a good, basic guide. But for minute detail of processor chips and powerful support chips, then take a look at the designer's 'Bible', the Usborne series of books titled An Introduction To Microcomputers. A trip to the library is recommended for these - or else you may have to sell your micro to pay for them! And you'll get similarly detailed information on most common TTL chips from the TTL Data Book from Texas Instruments. Texas also publishes books on linear circuits and memories. Most of these titles can be obtained from university or polytechnic book- shops, or if you're not that dedicated (or just a cheapskate) try the libraries again.
To summarise, for the beginner I would honestly recommend the Adrian Dickens and Stephen Adams books and, as you start to get more advanced - or start suffering from insomnia - the Sargent-Shoemaker tome. DIY computing is still in its infancy, but things are slowly changing and I've no doubt that sooner or later, the book- shelves of high street shops will be crammed with suitable publications. Try a little DIY ... it's as much fun as programming!
Can anyone tell me if it's raining outside ... ?


Spectrum Hardware Manual by Adrian Dickens, Melbourne House,
ISBN 0 86161 1152

Easy Add-on Projects For Spectrum, ZX81 & Ace by Owen Bishop, Bernard Babani,
ISBN 0 85934 099 6

20 Simple Electronic Projects For The ZX81 & Spectrum by Stephen Adams, Interface Publications,
ISBN 0 907563 112

Sinclair Spectrum And ZX81 Add-ons by Natasha Graham and Michael Roberts, Sigma Technical Press,
ISBN 0 905104 641

Interfacing Microcomputers To The Real World by Murray Sargent and Richard L Shoemaker, Addison-Wesley,
ISBN 0 2010 077 36

An Introduction To Digital Logic by A Potton, MacMillan Press,
ISBN 333 14679 4

An Introduction to Microcomputers, Usborne Press

TTL Data Book, Texas Instruments
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