A how-to on making a DIY USB MIDI to CV from DIY Synthesizer: This one is simple and does not require any expensive Teensy’s or STM32. It runs on the ATtiny85 using V-USB. The ATtiny is programmed with the Micronucleus bootloader and is firmware upgradeable incircuit. More details at DIY Synthesizer homepage.
The OpenPipe crew designed a MIDI-USB shield for the Arduino that can turn just about anything into a musical instrument. To demonstrate the shield they built the open source bagpipes in the video above. Via Hacked Gadgets.