| hardware world |
MONOLITH Electronics Ltd has produced an alternative disc system for the ZX-81. It will allow users to store up to 70K of programs or data on one disc. The discs are single-sided and at the moment only one disc drive is allowed for. The disc plugs into the back of the ZX-81 and the 1K RAM pack and printer are plugged into the disc unit.
That solves the problem of Sinclair address decoding, as the disc unit allows only the peripherals to appear in one place; the cost of the 5¼in. disc drive will be £200 and the first batch of 100 will be available this month. Monolith Electronics can be contacted at Crewkerne, Somerset.
BOLTON Electronics has another board for the ZX-81 containing a music chip and audio amplifier. The chip provides three channels and a noise generator, plus a 16-bit I/O port. The tones frequency and envelopes can also be programmed. The volume of each tone can also be changed and all that is required to listen to the cacophony is a loudspeaker.
The input to the onboard amplifier is also available, if you want to use an external amplifier. The cost of the board is £21.85 and it can be obtained from Bolton Electronics, Bolton, Lancs.
A PROGRAMMABLE colour character generator is available from Fountain Computers Ltd, Alresford, Hampshire. The board will also provide a static screen - separate from the Sinclair one - but programmable from Basic, so that other programs of other computers which rely on a display being on while it does some fast computing can be used. The cost has not been fixed but it will be from £50 - £100. The characters are compatible with Prestel and so Prestel programs could be expected to work on it without conversion.
AN EPROM board which will take up to four 8K EPROMs is available from Eprom Services. Fitted to the back of the ZX-81 between the computer and the RAM pack, it can be used to store machine code routines in common use. Those routines can be written by you - for the company to put into an EPROM - or the company can supply some.
Some of the routines available are RENUMBER, FILL, SPARE MEMORY and decimal-to-hex converters. The board fits in the 8K section between the 8K of Sinclair ROM and the RAM. The board costs £17.50 and the EPROMs for use on it cost £3 each.
The sockets on the board can also be converted to take 6116 (2K) RAMs instead of an EPROM, so the software can be developed before storing it permanently in the EPROM. Eprom Services is at Leeds.
THE BIG EARS speech recognition system is available for the ZX-81. The system consists of a metal box containing two frequency filters, a battery-driven condenser microphone complete with stand, and a DIN socketed cable to connect to your INPUT port.
Big Ears |
The only ports recommended by the firm are Technomatics, its own synthesiser board and the Redditch port. Other ports could be used, but their address would have to be inserted in the machine code routine used to obtain the voice from the frequency filter.
The system expects to have 16K of RAM attached to it and the port must be out of that section. The program reserves 256 bytes at RAMTOP for its own use and it is mainly a Basic program. The connection to the ZX-81 port must be done by soldering it to the port, as the DIN plug fits on to the frequency filter.
The system can be used to store voice prints, which are used to control the actions of the program. So shouting LEFT-a-bit, DOWN-a-bit could become common. Big Ears, costing £56.35, can be obtained from William Stuart Systems, Essex.
BYTRONIC Associates, which already produces a number of educational demonstration models which show how a computer can control things, has produced a port unit for the ZX-81. It consists of three ports on the one board, giving a total of 24 data lines, which can be set in groups of eight to either input or output information from the ZX-81.
Each line terminates in a screw terminal, so that external devices can be connected easily, using pieces of wire. The 16K RAM pack and other extensions are catered for, by duplicating the ZX-81 connections on the far side of the board.
Detailed notes and programs in both Basic and machine code are provided with the port. The addresses of the port are memory-mapped and so can be controlled for PEEK and POKE. That should suit schools, as the same firm can supply many devices which show industrial processes under the control of a computer.
The port costs £52.05 and Bytronic is at Sutton Coldfield, West Midlands. By the way, the people who run the company are teachers.
THE CHEAPEST 16K RAM pack for the Sinclair must be the one advertised by AVC Software at £32.50. It contains 16K of 4116 dynamic RAM chips and all the proper decoding for the RAM. It is the same as is being sold by several other companies, but this is the cheapest. It is only half the size of the Sinclair RAM pack but it is likely to be more reliable, as it has a tighter edge connector and no transformer to give that horrible buzz. The unit is guaranteed for six months.
AVC Software can be contacted at Birmingham and please mention the Educational ZX Users' Club, as the coordinator has been promoting it because he receives £1 per mention.
A KEYBOARD is now available from Redditch Electronics, which will provide push-button keys in kit or ready-made forms. The company also can fit it into a small plastic box, which is big enough to take the ZX-81 PCB. The correct keywords and all the graphics are shown under clear plastic covers on the ¾in. keys.
The connections to the ZX-81 are via a ribbon cable and two plugs which fit into the keyboard sockets on the PCB instead of the Sinclair ones. The keyboard is simple to fit and Redditch gives clear drawings on every stage of fitting it to the ZX-81. The keyboard costs £20.50 for the kit and £25.75 for the made-up keyboard. The case costs £10.30; all prices include VAT. Redditch Electronics, Worcestershire.
WATFORD Electronics wants to have computers to use the same motherboard and has produced a set of boards which it says will fit the ZX-81, UK-101, Superboard, Acorn, Pet and Tangerine. The motherboard costs £42 and there are already five 'daughter' cards available. They are sound card for up to three AY-3-8910 music ICs - one supplied; PIO card using 6520 VIA chips; PROM card for 8K of EPROMs - 2716 or 2732; and a PROM programmer for +5V PROMs.
The boards vary in price from £23 for the PIO card to £29.85 for the PROM programmer. Watford Electronics is at Watford, Herts.
TECHNOMATICS, which produces a port for the ZX-80 and ZX-81, is now producing a low-priced PCB for extending the connections from RAM packs. The board is approximately 1in. wide by 3in. long and has the same fingered edge as the ZX machines on both sides.
A slot is cut in the correct place. That means that if you have a RAM pack, like that of Sinclair, or port which does not allow you to connect other things at the back, the PCB can be soldered on to the back of the edge connector to duplicate the expansion port of the computer. The cost of the PCB is 25 pence.
Technomatics has two shops - London, W2, and the main shop at London NW10. It can also be used to connect Vero-type prototyping boards to a motherboard which uses edge connectors.
UNIVERSITY Computers can now provide a board which plugs into the ZX-81 and not only an analogue port but an EPROM socket and a real-time clock. The port is in two sizes, A and B options. A consists of the analogue port and the EPROM socket. Option B includes the real-time clock as well. A Veroboard experimenters' board is also available from the same company for £7.50, complete with suggested circuits. A free consultancy service is also offered to customers.
Option A costs £49.95 and Option B, including batteries, £66.20. An upgrade kit from option A to Option B is available for £30. All prices quoted are for built and tested units. University Computers, Cambridge.
THE CF81 is a cassette filter for ZX-81s from G M Harris. It contains two filters and an amplifier in a box 2½in. x 2in. x 1 in. The way that the ZX-81 records a tone on tape can cause a 1kHz signal to be generated on top of the ZX-81 data. The low-frequency filter copes with that.
The other frequency at 12-14kHz can be caused by the fact that the tape heads oscillate at that frequency and the ZX-81 recorded frequency harmonic can clash with it, creating yet another frequency. The unit is powered from the power pack supplying the ZX-81 by plugging it into the ZX-81 ear and power sockets. The cassette leads and the power supply plug into the other side of the box.
Whether or not that happens on your tape recorder, it is certainly cheaper at £9 than buying a new tape recorder. G M Harris is at Farnham, Surrey.