Arduino USB to Legacy MIDI Converter

This project allows sending MIDI signals from a USB-only keyboard or controller to a device that only has 5-pin MIDI IN. I’m not the first to do this - I think it was first hacked by my secret idol, the famous Collin Cunningham, back in 2010. However, the way I did it is perhaps different enough to be worth sharing, or maybe someone knows a better way to do this now and will school me. MIDI is a protocol that musical instrument controllers like keyboards, keytars, electronic wind instruments, or any old thing can use to talk to devices that produce sound - such as other keyboards with built-in sounds, synthesizers, computers, etc. Like rubes, we used to use these clunky 5-pin DIN cables to carry MIDI, but now the slick way to do it is MIDI over USB. Many newer controllers only have USB, which they use for both power and MIDI. This is a problem if you want to talk to something that only has a 5-pin jack for MIDI IN. This is true for most keyboard synths (why build a USB host into it?) and for may DIY synths one might build (legacy MIDI is a lot easier to DIY). I specifically wanted to control my nice Nord synth with my keytar, which has a little wireless USB receiver.”