The AVR SYNTH is a monophonic "virtual analog" synth based, originally, on the Atmel AT90S8535 microcontroller and was designed by Jarek Ziembicki. His aim was to check to see if a simple micro could be used for sound synthesis purposes. And the result? The AT90S8535 managed to do all the tasks: service front panel switches and pots, receive and process MIDI messages, and sound generation!
This MK1 designs uses a PCB front and rear panel and requires hard-wiring between the Controller PCB and the panel components
AVRSynth Datasheet and Build Guide