I´ve been planning to build the Arduinoboy midi interface since sometime last November. I finally got around to breadboard a version yesterday using a 4n35 optocoupler. Works like a charm!
The original “schematic” (that uses a 6n138 optocoupler) and the arduino code is located here
I used this instructable as a basis for the midi in part
When I ordered my arduino a couple of years ago, I also bought 2 atmega8 chips that were prepared with the arduino bootloader. So, I figured that the next logical step would be to freeform (ie solder the components together without a circuitboard) a minimal arduinoboy with one of those extra uc:s. This would allow me to comfortably install the device into the battery compartment of my DMG.
There´s some info on the minimal arduino setup here
http://www.arduino.cc/playground/Learni … Standalone
The only thing I didn´t have at home was the crystal, so when it arrives I´ll write up an instructable or something.
The next steps from there would be to power the gameboy, midi keyboard and a small active speaker from the same rechargeable battery. Slap it all together with some tape and firewood, quit my job and play music in the street.