Download https://www.arduino.cc/en/software https://www.pjrc.com/teensy/td_download.html WARNING: modify your code and verify it before you push the reset on the teensy, to make sure it works. Use my version of control-surface uploaded here. That version has modified .hpp files that are crucial for making this code work on teensy 4.0 xp120. The default code scans lines too fast … Continue reading How to use MIDI with arduino or teensy