What is it?

This is a self assembly Z80 based computer kit. It is compatible with the Sinclair ZX80 computer released in 1980. It follows that design closely, with a few concessions to modern parts.

The board is designed to be the same shape and size as the ZX81 board, allowing this to be fitted into the case of a broken ZX81. Note the TS1000 case is similar, but the video output is in a different location, so a TS1000 case would require modification.

This version could also be used stand alone with your own keyboard or an aftermarket ZX81 keyboard.

This is a tried and trusted design, I have been selling these for almost 10 years. The kit comes with all new modern parts which should mean every kit built works first time.

The Z80 has now been discontinued, but I have secured stock from one of the last batches of Z80 CPUs. All kits will be supplied with Z80s from that batch, date code 2427. While stocks last as they say.

Why did you make it?

An original ZX80 is difficult to find and very expensive, and not necessarily functional. This is an opportunity to build and program one of the first home computers.

What makes it special?

The upgrades from the original design include a full 16K of RAM on board. A ROM chip with the option of four ROM images, such as the original ZX80 4K Integer BASIC ROM or the later ZX81 style 8K Floating Point BASIC ROM. Optional overlay stickers are available with 4K and 8K BASIC keywords in ZX80 colours.

Note that like the ZX80, this does not include NMI "slow" mode, that was added for the ZX81. For that see my Minstrel 3 kits which are fully ZX81 compatible.

The video output has been switched from a UHF modulator designed to drive a TV set to a composite video output that should suit a variety of TVs and monitors. It does not include a colour burst signal, so may confuse some composite to HDMI adapters. Jumpers can be used to select 50Hz or 60Hz frame rate for PAL or NTSC regions, and normal or inverse video.

The video signal has been cleaned up by an additional 74LS74 IC which buffers the sync signal, adds the missing back porch to the video signal. It also adds pixel synchronisation to ensure even sized pixels and no glitches from adjacent inverted and non-inverted characters. These improvements make very good solid picture on a modern LCD, just like the original would have been on a 1980s black and white portable TV.

Power is by 9V DC 2.1mm jack. Current consumption is around 100mA. Jumpers select either centre negative (ZX Spectrum, Commodore 16, guitar pedals) or centre positive (everything else).

The kit includes a 7805 replacement switching regulator. There is space to fit a 7805 linear regulator if you want authenticity. This requires a heatsink, the one from the donor ZX81 will do nicely. Fit one or the other, not both.

All through hole parts are used making this kit suitable for an intermediate level kit builder upwards.