| hardware world |
THE ZX-81 video invertor consists of one integrated circuit, which is an npn transistor array, seven resistors and one coupling capacitor, all contained on one small PCB - 20mm. by 32mm. - which probably is manufactured using a Photolac process. The idea behind the device is to reverse the conventional display to give white characters on a black background, a switch being provided to return to normal display mode.
The PCB is held in place by a strip of double-sided adhesive tape on top of the logic chip IC1, although that is only for location purposes. The device works by intercepting the signal to the modulator and installation requires the cutting of a wire to the modulator and soldering of our wires in appropriate positions.
The toggle switch is fitted to the rear of the ZX-81 case and a ¼in. hole has to be drilled to accommodate it. Many Sinclair users may be justifiably reluctant to drill holes in their ZX-81s so it may be possible to locate the switch in a different way, or perhaps omit it completely and stay in inverse video mode.
The invertor costs £3.50 and is available from Dieter Fritsch, Cheshire.
A similar device is available from B A Reader to the one just described but consists of a single IC and a rather over-sized toggle switch, both being mounted on a small piece of Veroboard. The manufacturer has indicated that a smaller switch is now supplied with the kits. Installation again consists of drilling a hole located on top of the ZX-81 case - although space immediately below the switch is very limited - and cutting a lead to the modulator.
This inverse video switch costs £3.75 built and £ 2.95 as a kit and is obtainable from BA Reader, Birmingham.
ADH display interface |
ADH SYSTEMS has produced an interface which allows a ZX-81 to control a LED or filament lamp display for advertising in a shop window. The system can control a 16, 24, 40 or 80-column display and is not limited only to numbers or figures. The display is seven LEDs high and can be used to display anything which fits on the column x 7 format. The displays are available as a kit - LED boards made up - or ready-made for between £62.01 and £356.50, including VAT, interface and program to run it.
THE Fulcrum ZX-81 Bleep consists of a small PCB measuring 3½in. by 2in. which fits into the space inside the ZX-81 case, underneath the keyboard. That particular space is much favoured by other manufacturers for their add-ons, so it could be difficult to fit any other device there since the heat sink is close to it.
The sound, which is a short bleep, is made by a small transducer which is located in one corner of the PCB. Fulcrum emphasises that the device requires no soldering, the connections to the ZX-81 being two wires for power and a 5-way flexible cable which plugs into the existing keyboard tail socket.
The device works in both FAST and SLOW modes although it does not function on certain shifted keys.
Since the review was done the company has brought out the ZX-81 Keyboard Bleeper which covers all 210 characters.
The ZX-81 Bleep and the ZX-81 Keyboard Bleeper are both priced at £8.95, including VAT and postage, and can be obtained from Fulcrum Products.
ELLANBEE (Graphics) can provide a cure for tired eyes from too much staring at a bright TV screen. Colourscreen is a large, coloured, optically-clear plastic sheet which goes over the TV screen. It is a 15x12in. sheet which is cut to fit the size of your TV screen and then fitted carefully over it.
It requires no tape or other fixing and can be removed at any time. It is in two colours, blue or green, with instructions and a specially-stiffened storage envelope, at a cost of £2.95. Larger sizes are available on request from Ellanbee (Graphics), Co. Durham.
PRINT-N-PLOT Products, which produces a display mapping book and foils, is now supplying printer paper for the Sinclair printer. Silicon Tricks is not now supplying paper, so this would seem the only alternative to Sinclair.
The quality is as good as, if not better, than that of Sinclair and at £ 10.95 is cheaper. Print-N-Plot is also selling a book on computer graphics at £1.50. All prices are inclusive of VAT, and paper can be obtained from various ZX computer shops.
EAST LONDON Robotics has produced a incremental RAM board which allows you to add up to 16K of static RAM in 2K portions to a ZX-81. The board fits inside the ZX-81, and can be used with any RAM pack available. It requires no soldering to fit the board and its instructions cover nearly every possibility.
The board uses 6616 static RAMs and can be addressed into any position in the memory map. The 8K incremental board costs £12.01 and the 16K £ 13.23. To that must be added the price of the RAM chips at £4.93 and 45 pence for postage if the order is less than £15.
STRIPELAND LTD has produced a computer interface for the ZX-81 which can control another device in another room without wires between the two. The mains wiring is used to transfer a signal from the micro to the remote control unit attached to another device.
At the moment the computer can only send signals and not receive them via the system but modifications to produce a two-way device will be available soon.
The ZX-81 computer interface costs £61.40 and the remote control £27.50, inc. VAT and postage. Stripeland is at Merseyside.