Digital/Analogue Converter
Eprom Services
1983

BITS 'N' PIECES

My, how it's grown - almost a MegaSpectrum! Which of these useful little add-ons could you do with on your Speccy? To help you choose, Stephen Adams has done his bit and come up with a piecemeal review of them all.

1. A/D and D/A BOARDS
EPROM Services/£23.95-£57.95 (A/D), £26.95-£54.95 (D/A)

The A/D board allows you to digitise the voltage input into a number the computer can then understand by changing it from an analogue reading to digital number. The D/A board lets you send out a voltage that's not digital (not just on or off). You can use the D/A board to send voltages to control things like amplifiers or train sets - speeding the trains up or slowing them down. In schools and labs these boards are often used to replace the voltmeter, ammeter and resistance meters - that way they can have an accurate computerised version that's able to take several versions at once. You can even use the boards with a simple Basic program to find out where in the circuit something's happening.

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REVIEW BY: Stephen Adams

Blurb: ZXSR Note: The following items were also reviewed but are "general" hardware that do not, and probably shouldn't, have a ZXDB ID. They are added here merely for historical accuracy. 2. SOUND BOARD Various £15-55 You'll find sound boards in all sorts of shapes and sizes but they all basically use the same chip. AY8910 (or ATY8912). So. If you want to let rip with a guitar riff on your Speccy, let me explain how they work. They provide three different oscillators (or voices as the cool dudes in the music biz call 'em) and a noise output that can produce anything from pips to sea sounds. You can program the oscillators to produce any audio tone and mix them all together to form music or background sounds to your games. You can even use a sound board as the basis for a very cheap synthesizer. You can add to the basic set-up so that you've got more notes to play with and the output can repeat any rhythm or note at varying pitches while you tinkle out the rest of the tune. And the big plus if you're into games is that this needn't keep you from the joystick as the chip will carry on producing the last note until you reprogram it. Choose a sound board according to your needs and wallet but one tip is to go for one with a good amplifier included - the output from the chip is much too low to hear at all. 3. SP ROM UPLOADER Cambridge Microcomputers £29.95 This uploader contains two sockets for 8K or 16K ROMs or EPROMs so that they can be transferred to any place in memory at the push of a button. You can also go straight from power up into a program without recourse to LOAD "". The advantage of EPROMs is that they can contain anything you like, but you must use an EPROM blower. How about using them to change the character set or run an automatic program in conjunction with a timer that turns on the Spectrum or even to run advertisements in shop windows - well, I've done that anyway! 4. INPUT AND OUTPUT PORTS Various £15-35 These are the arms and legs, eyes and ears of a computer. They allow it to find out just what's going on around it. You can connect up an input port for use as a joystick, a weather station reader, a light pen or even sensors for a burglar alarm - and that's just a few of the uses for this versatile board. The outputs are used to control relays that can operate lifts, dial the telephone or control a robot arm. The limits of the input/output port are your own imagination. 5. PRINTER INTERFACE Various £30-£50 As add-ons go, this must be the most popular one after the joystick interface. The interface can come with tape software that has to be loaded up before you use the unit, like the one shown, or with a controlling EPROM built in, like the Kempston E interface. Whether you choose a top-notch daisywheel printer or a slightly more down-market dot-matrix, it'll usually come with a Centronics socket for the interface to plug into. Mind you. If you find that the printer you've chosen has a serial interface then you'll have to lay your hands on an RS232 interface. You may find the choice limiting, though. While there are as many Centronics interfaces as there are printers, the number of RS232 interfaces is basically limited to the Interface 1 and ZX LPrint versions. If you want to go in for screen copying, you'll find that it's been brought to a fine art with units like the Kempston E but with serial interfaces screen copies are still a shady area. 6. EPROM BLOWER Cambridge Microcomputers £29.95 You'll find one of these boards very useful if you want to store any of your programs semi-permanently. It can handle data up to a 16K limit and works by creating ROM chips which replace Basic, so that you can upload a program almost instantly - though you'll need a ROM SP uploader for that Programs stored like this can't be altered by POKEs or by turning off the power. You'll need four 9 volt batteries to program it but it'll usually run on - 5 volts from the Spectrum. If you want to reprogram it. you'll have to put ultra violet light through the window in the top - that's the only way of wiping the ROM clean. This is certainly a great way of storing your favourite routines but, unfortunately, it just doesn't have the capacity to save most machine code games.