Tim’s got a pretty cool sounding home made synth, he calls it the cheapsynth. He is using a keyboard from the game rockband on the wii, and an arduino. Amazingly these keyboards have MIDI on them already so technically this hack should work with other MIDI devices.
Currently it looks like it supports 2 note polyphonic output with options like square, saw, and portamento. I’ll be honest I’m impressed with the sound coming out of this. I’m off to eBay to buy one of these keyboards myself and put this together. :)
Source code to the arduino sketch is available here on github.