Since the 1980s, MIDI has been a great way to send data between electronic musical instruments. Beginning as a modified serial interface running through optoisolaters and DIN sockets, these days, your hardware is more likely to carry its MIDI data over USB instead. This is great if you want to hook up to a computer without a cumbersome interface, but not so great when you want to connect a bunch of instruments to each other.
The Roland Integra 7 is a rack mount synthesizer with classic MIDI ports. [adriangin] wanted to control the synthesizer over MIDI, but their Casio keyboard only had MIDI over USB available. To get around this, [adriangin] set out to add a standard MIDI Out port to the Casio PX410R.
