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ZX80/81 Homebrew Clone

Recreation of a Sinclair ZX81 (dual rom 80/81) based on Grant Searle's project.

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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 :)

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). 

TK82C (ZX81 Brazilian Clone)
TK82C (ZX81 Brazilian Clone)

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.

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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keyboard_mask.pdf

A4 Paper 1:1 Scale of the Keyboard Mask

Adobe Portable Document Format - 356.59 kB - 03/12/2022 at 12:59

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    Schematics

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Discussions

Cees Meijer wrote 05/11/2022 at 09:48 point

Very Nice! One step up from my project: 

https://hackaday.io/project/170707-zx80-replica

But I'm tempted to build a real clone using your PCB...

  Are you sure? yes | no

Augusto Baffa wrote 05/11/2022 at 17:32 point

I've printed the zx80 case (same project u did) but never assembled it xD

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Juan Castro wrote 03/17/2022 at 19:55 point

MUITO legal! Pode ter certeza que será mencionado no próximo Repórter Retro! - http://retropolis.net.br

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Augusto Baffa wrote 03/19/2022 at 16:17 point

bem legal! eu sempre ouço :)

  Are you sure? yes | no

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