This is the most musical demo I’ve seen of the cheapster DIY Gakken SX-150 synth. 

On the video, I’m using Ableton Live to send midi data to the processing sketch using a Network Midi connection on the Mac. On windows, you should be able to use Midi Yolke to accomplish the same thing. Then, I make sure that the processing sketch receives midi on that same virtual midi connection and sends the data through serial to the arduino. So, depending on your system configuration, you might have to tweak the Processing sketch a little bit to make sure it is reading and writing to the right midi and serial ports.

The flow of data from the sequencer to the synth looks like this:
Ableton Live => Virtual Midi Connection => Processing Sketch => Serial Port  => Arduino => DAC => SX-150

The SX-150 is turning out to be a great platform for hacking and learning on; if you fry your kit, you’re out the equivalent of a couple of pizzas. 

via MrBook