Natrium42 posted schematics, pictures and brief instructions for connecting MIDI input and output to DS to the DSerial Wiki. MIDI output is very easy, because it requires no components besides wire and a 5-pin DIN connector. MIDI input, on the other hand, requires a 3.3V optocoupler because MIDI uses a current loop to prevent introduction of noise.

http://natrium42.com/blog/?p=48