Hello all. I'm pulselooper friend, the one who's helping him to build the arduinoboy. Communication between arduino and gameboy is working, and when arduinoboy is in LSDJ Slave Mode it works (so MIDI In is working too), but we can't figure what is happening with MIDI Out. We put arduinoboy in LSDJ Master Mode, and LSDJ starts playing, but there's no MIDI signal in MIDI Out.
I don't have an oscilloscope, so I used a voltimeter to see it was any difference in the signal (dumb, I know, but you need to use what you have 
). The GND is 0V, the other two are +5V (4.83V, to be more precise) in standby. When LSDJ is started, voltage drop to 4.7V, so I guess arduino is sending the signals. But no MIDI events are registered.
So, we managed to do the complicated part (and it did take some time to understand the optoisolator), but the easy part is not working. Any guess?