Here's a link to the original circuit by gwEm: http://www.preromanbritain.com/gwem/lsdj_midi/

And here's a link to firestarter's advanced interface: http://www.firestarter-music.de/lsdj/

And the Arduinoboy interface: http://code.google.com/p/arduinoboy

And the MCG interface: http://gieskes.nl/master-clock-generator/