The Simple 4-Bit Computer

A modular computer with a vintage look.



  • Atmel AVR microcontroller (ATmega328P) programed in pure AVR C
  • TLC5940 IC to drive the LEDs
  • 3D modeling with Fusion 360


What I like most in computing is the low-level stuff. Thus I have always been attracted by the computer’s beginning era, with its TTL logic circuits, its assembly languages, its various architectures…

After making the Kenbak−1 Replica, I saw Galactic Electronics’ “4 bit CPU”. I now wanted to make my own 4 bit retro computer, with LEDs and switches (because that’s just the coolest way to interact with a computer), programmable in machine code (in assembly language by extension). No wired logic inside but only a simple microcontroller.

I hope I will later find the time to make a computer entirely made of logic integrated circuits like this one, very raw, or the Magic−1, quite complex or even that one from Ben Eater, entirely made on breadboards, with excellent explanations.

This project has evolved and should probably be called “The Simple Modular Computer”, as it can now emulate other computers like Galactic Electronics’ 4 bit CPU or that good old Kenbak−1.

Making of the case

3D model made with Fusion 360
Milling CNC programming
Milling of the case
Case milled
Cutting the overlay with a scalpel
Sticking the overlay to the front panel with double-sided tape
Starting to make the electronic circuit
Attaching and soldering LEDs and switches
Front panel finished!
Wiring finished!