As more and more people buy ZX-81s, more and more companies are bringing out add-on products. Each month we will look briefly at what has arrived recently on the market.
NOW a kit for a ZX-80 which will allow you to have a constant static screen when used with the 8K ROM. Compshop will not assemble kits or attach them to a ZX-80. The kit is for the ZX-80 enthusiast who can use a soldering iron, as it takes care and patience to fit it inside the ZX-80 case.
It stops that annoying flicker when accepting an INPUT or entering a program from the keyboard. The top line will tend to slant to the left and the power supply may have to be changed, as the unit draws 300ma from the +5V regulator but the cost is only £15.99.
Compshop Ltd, Hertfordshire. There are Compshops in the U.S. and the Republic of Ireland.
DATA-ASSETTE has launched the first of its hardware add-ons for the ZX-81. Called the ZX-99, the device slots into the expansion board and according to the company gives the ZX-81 real computing power.
Four tape recorders can be handled at one time and business applications are now within reach.
The ZX-99 also provides an RS232C serial output interface which allows a wide range of printers to be driven.
The ZX-99 is available from Data-assette, London.
Part of the range
THIS COMPANY was one of the first to introduce a motherboard, so that other things could be connected to the ZX-80 or ZX-81 when the 16K or other memory pack was fitted. Since then, a range of goods has been produced, from 3K RAM packs at £18 to sound and programmable graphics boards. All the boards, apart from the RAM, will plug in either direct to the ZX-81 via a QS connector - a double-sided edge connector - or into the motherboard.
The sound board also has included a 16-bit port which can be used to control devices external to the ZX-81 by PEEK and POKE commands. The boards are all supplied with very clear, easy-to-understand instructions and Quicksilva provides test programs for each unit.
QS motherboard £12; QS sound board £26; QS CHRS board £26; QS RAM from £18 - £35. Quicksilva is at Southampton, Hampshire.
THIS UNIT will allow ZX-80 or ZX-81 owners to put any audio sounds through their TV loudspeakers. The sounds can be fed-in from a tape recorder - instructions for using the program perhaps? They can also be used to give Space Invaders real explosions.
The kit requires the use of a soldering iron to attach it to the ZX-81 video modulator but derives all its power from the internal +5V regulator. The kit is a metal box which fits on top of the modulator inside the ZX machines. A separate audio lead which can be plugged into a tape recorder ear socket or the output of a sound board is also provided. The audio transferred in the slow mode is unaffected by the ZX-81 computing.
The audio modulator costs £10 and is available for Compusound (U.K.), Worcs. It is called a Telesound 82.
THIS PROFESSIONAL keyboard is from a manufacturer of keyboards for the computer industry generally. It consists of 46 microswitch keys with the correct stepped arrangement for a QWERTY keyboard. It requires no soldering to attach it to the ZX-81 - only the opening of the ZX-81 plastic case and the insertion of the replacement leads.
It is complete with instructions. Forty keys are labelled with the Sinclair codes, leaving six spare keys for the user and the space bar unmarked. The overall dimensions are 10in.x4½in.x2in.
The cost is £28.95 for the keyboard and £43.95 for the keyboard in a metal case. Computer Keyboards is at Ascot, Berkshire.
THIS tape recorder has been designed by a manufacturer of floppy discs to eliminate the problems with LOADing and SAVEing tapes. Each tape recorder, which looks the same as any portable tape recorder, is tested and sold complete with a certification tape. The ECR81 has a long-life recording head adjusted for the correct alignment to TDK Cr02 high bias tapes.
It takes the data from a tape and passes it through a special circuit, so that tape variations cannot affect the data LOADed into the ZX-81. The output is through a DIN socket. Program names can be entered for recording on tape through a condenser microphone fitted within the tape recorder.
The ERC81 recorder can be obtained from The Monolith Electronics Co Ltd, Somerset.
A MEMORY-MAPPED port which can be PEEKed and POKEd from a Basic program located at 11,000 for the ZX-81 or 25,000 on a ZX-80. That means that it cannot be used with the 16K RAM pack on the ZX-80; the 16K RAM can be used only on the ZX-81. That port allows the user access to control printers, to light LEDs, to use joysticks. Technomatic can also supply a booklet of applications for 40 pence if you want some ideas. Demonstrated at the ZX Microfair was the use of the OUTPUT port to generate tones through an external loudspeaker. The INPUT and OUTPUT ports are mounted on a printed circuit board which plugs into the back of the ZX machines, so an extra printed circuit board will have to be used to attach the 16K RAM pack - also obtainable from the same firm.
Technomatic can be contacted at London NW10. The port costs £18.
Controlling your tape.
THIS BOX has one switch to control all your tape recorder functions. LOADing and SAVEing, cueing the tape up to the correct position and inserting a voice on to the tape all have one switch position. Cueing is done by listening to the tape via the amplifier and loudspeaker included in the unit. The same loudspeaker is used for a talk-in before the program starts.
Feedback causing hum or a high-pitched tone on recordings is eliminated by switching off the ear connection when SAVEing. Therefore all the leads can be left plugged-in all the time.
The unit is also supplied with 70 centimetres of cable so that the tape recorder does not have to be sited next to the ZX machine.
Abacus can be contacted at Swansea, West Glamorgan. The controller costs £12, including postage and packing.
THIS RAM pack fits on to the back of a ZX-81 to give 32KB of memory for use by the Sinclair 8K Basic. The original 16K can be expanded to 32K on the ZX-81 by altering the RAMTOP variable and giving the command NEW. After that is done there is 16K for programs and 19K for variables and data.
Audio Computers now supplies some programs for storing the screen and program in high memory above RAMTOP. That allows you to change the screen within a program and swap programs stored in RAM. It is not possible with the programs just to swap the variables (data) to a new program.
Audio Computers is at Southend-on-Sea, Essex. The 32K RAM pack costs £46 for a kit and £54 ready-built.
THE FULLER DP system consists of a keyboard unit which contains your ZX-80 or ZX-81 printed circuit board and a keyboard made up of 40 microswitches in the same layout as the Sinclair flat keyboard. The tops of the keys are stepped and have on the key-tops the same symbols as the Sinclair keyboard, covered with a clear plastic top to prevent wear.
The system can be built up using the 16K RAM pack and a motherboard which will accept any boards which will plug into the standard 23 x 2-way edge connectors.
The power supply can be fitted inside the case and can reduce the number of cables required to connect the unit. The system requires only a screwdriver to assemble unless you have ZX-80; if that scares you, Fuller will do it for £10. The basic system, which consists of the cased keyboard, costs £32.75 as a kit or £38.75 built.
Fuller Micro Systems is at Liverpool.
IF YOU become disinterested in Space Invaders looking as if they were made from Lego, you can, with this board, swap Sinclair letters and characters for proper Space Invaders. It fits beneath the keyboard in the ZX-81 and requires three soldered connections to the ZX-81 printed circuit board. If that worries you, send the ZX-81 with an extra £3 and it will be done for you.
There are 448 extra characters within the ROM which require no special taped program or RAM to use; a simple instruction of LET X=USR(??????) is all that is required. There is a spare socket on the unit so that graphics symbols of your choice can be used. A RAM chip - 4118 or 6116 - must be inserted in the socket to store all these user-defined characters.
The 4K graphics ROM and printed circuit board is available for £30.95 from dK'tronics, Gt. Yarmouth, Norfolk.
Plenty of facilities for RD.
THIS SYSTEM, usable on the ZX-80 or ZX-81, consists of a motherboard into which cassette case-type modules plug, giving extra facilities. The motherboard consists of a connector to plug into the ZX machine and vertical printed circuit boards on to which the modules fit. The printed circuit expansion port at the back connects to the 16K RAM pack. There are two sizes of motherboard, the Micro-mum which will take two boards and the Super-mum which will take eight boards. The unit is supplied from the ZX machine +9V line via its +5V regulator. All the devices from light pen to analogue and digital inputs are available through PEEKing and POKEing location 15360 to 16383. The Mini-mum costs £15.80, the Super-mum £40.80. The modules cost between £23.30 and £33.30.
RD Laboratories is at Ware, Herts.
All prices in this review are rounded-up to include VAT at 15 percent and p&p.