ZX81 – out of the box

It must be an age thing but I’ve recently started (investing?) in retro kit, from the 1990s, 1980s and earlier. This has included hifi (including recently a superb Pioneer A400 – http://www.gbaudio.co.uk/data/a400.htm) amplifier, and vinyl LPs, but one item that I’ve had on the list for a while is a Sinclair ZX81 home computer. I bought one of these in 1982 and it kick-started my interest in programming and ultimately set my career path in software development. I still do most of my commercial programming in VB.Net  – a distant relative of the simple BASIC that the ZX81 provided.

There are plenty of machines for sale on eBay and I eventually got one for around £20, still in its original (though tatty) box. No 16K RAM pack but these are also easily sourced. I can’t see myself with the time to write 16K of code on that keyboard again but you never know. The first problem is going to be sourcing a suitable TV – the output from the ZX81 isn’t compatible with modern LCD TVs and that’s all we have. We did have an ancient 14in black & white TV but that got caught up in a pre-Christmas clear out – it would have been ideal.

Undeterred, I connected up to a nearby Sony 30in LCD TV, retuned the analogue signal and was amazed to find the little square K cursor appear but the overall display was virtually unreadable. I did manage to write a 4 line routine to prove it all worked though: –

10 INPUT A$

20 IF A$=”” THEN STOP

30 PRINT A$

40 GOTO 10

(My first attempt missed out line 20, resulting in an unstoppable loop and a reset.)

Next task is to find a suitable display…