Building a PS/2 to Commodore 1531 mouse adapter. I still need to tweak the resistor values in the pot X/Y lines, but otherwise it's working pretty well. The code is from the mouse1351 project - https://www.github.com/svofski/mouse1351

This is a fantastic alternative to buying the prohibitively expensive Commodore 1351 mouse. Svofski's code is targeted for Atmega8.

At some point, I'd like to port it to an Atmega328 so it's more accessible...not everyone has an eeprom programmer, but many have an Arduino.