Michael likes his vintage organ KORG CX-3. It sounds good and keyboard feels right to play. But in early 70s there were no MIDI. But today almost any electronic music instrument comes with MIDI or other output interface. He decided to add a MIDI to CX-3 organ. For getting data you normally need to detect each key pressed. Luckily Michael found a great source on Internet with schematics where couple ICs are connected to keys that generate serial data stream. This gave him an access to keys by using couple of wires.
Next step is a midi interface. Attiny2313 seemed to be enough for generating MIDI. A home made PCB looks really great next to vintage organ schematic and it does job well. To see how to generate MIDI on AVR check out this resource on AVRfreaks.