ZX81 project

I have a mixed relationship with electronics and IT.

My first proper job was with the project that was created to support the one computer (usually a BBC Micro) that was being put into all UK schools in the early '80s.

It wasn't until quite a bit later that I had a computer of my own - it was a lot humbler - a Sinclair ZX81 which I paid £20 for in a charity shop in the late 80s.

Not a very impressive bit of kit, but it was fine for my purposes - not to become the greatest machine code programmer, but simply to understand a a little of what's involved in making a microprocessor "talk" to the outside world.

A key advantage of its being very slow (1MHz approx) was that I could get away with a very amateurish style of construction.

I wish I still possessed the sort of eyesight that allowed me to lay out printed circuit tracks actual size - 0.05 inches between chip pins !

Board 1 EPROMs and I/O ports. (Note how I solved the "loose 16K RAM pack" problem by rewiring the whole thing with BBC Micro-style connectors.)

It was ridiculously over-specced - something like 64 inputs and 64 outputs - though I never actually got any further than flashing 8 LEDs ...

Board 2 "analogue" -

1.serial I/O (my intention was to use it to decode morse and teleprinter signals on shortwave).

2. Phoeneme speech synthesiser. I actually made it say a few simple things

3. stereo music synthesiser

there was probably going to be A : D and D: A convertors on it too ..