ZX80/81 Homebrew Clone

Description

The Sinclair ZX81 was my first computer, I learned how to program (in basic) using this machine in late 80's. It's a master piece of simplicity and ingenuity. Of course, the ZX Spectrum brought colors and sounds but even the ZX81 had expansions like Chroma and Zonx. I believe that every hobbyist who would like to learn how to develop their own projects should start by studying this machine as it presents a simple and easy way to understand a computer architecture.

... and... yes... that's exactly what I did :)

Details

I started designing retro computers in January 2021. It all started because my first computer was a Microdigital TK82C (a clone of the Sinclar ZX81).

I learned to program on it and had so much fun programming simple ascii games. I missed my little friend and would like to still have it with me... Well... during pandemics, I was chatting with a friend via Zoom and told him my story... He had his ZX81 and gave it to me. Of course, after many years over the closet it wasn't working.

Since I couldn't use it, I started to study the ZX80 and ZX81 schematics to learn how it works and try to fix it. Then, after reading Grant Searle's page, I realized I could create my own clone. \o/ Yey... and my ZX81? I could fix it later. :D

This led me to study other computer architectures and then I started to create my own projects...

The eagle files and gerber I used were created by Wilco2009 (Alejandro Valero). But there are some changes I made to improve the sensitivity of the cassette and another one that I had to do to fix the video output.

I'll update the eagle files asap to add them but the mods are already in my schematics. I also sent some suggestions to Wilco and He added to his post on his blog.

For now, I'm working on Baffa-2 Project but I have plans to create some peripherals like zonx (soundboard clone shown on video bellow), sdcard reader, vga video output, etc.

Files

zx80_build034.routed GERBER.zip

Wilco's Gerber Files

x-zip-compressed - 471.58 kB - 03/11/2022 at 21:15

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zx80-81_build034.routed_eagle.zip

Wilco's Routed Eagle Files

x-zip-compressed - 221.95 kB - 03/11/2022 at 21:15

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Schematics_ZX80_81_Printable.PDF

ZX80/81 Schematics by subject

Adobe Portable Document Format - 118.80 kB - 03/11/2022 at 20:29

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ZX81_Complete_printable.PDF

Complete Schematics in A3 page

Adobe Portable Document Format - 100.11 kB - 03/11/2022 at 20:15

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Esquemas_ZX81_ULA_Andy_Rea_printable.pdf

ZX81 ULA Explained by Andy Rea

Adobe Portable Document Format - 87.14 kB - 02/23/2023 at 13:24

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Project Logs

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ZX81 at RetroRio 2022

Augusto Baffa • 04/04/2023 at 15:11 • 0 comments

ZX81 on Baffa-2 Homebrew Microcomputer

Augusto Baffa • 11/28/2022 at 19:07 • 0 comments

A set of boards based on this project was my first design of boards for Baffa-2 Homebrew Microcomputer. As I already had my Homebrew Zeddie I decided to prioritize a CP/M machine.

Now Baffa-81 is done :) more information at https://hackaday.io/project/188406-baffa-81-zx81-compatible-computer