Here is the MIDI-In, MIDI-Out and MIDI-Thru board for the Arduino. It is made with the opto isolator 6N138 and the inverter 74LS04N. To prevent bootloading confusion (with older Arduino boards) always powers the opto isolator over the Arduino.

Depending on the position of the jumper on the board the second MIDI socket can be used for MIDI-Out or MIDI-Thru. Two LED indicates MIDI-In and Out. One if the board is powered.

An older version and the schematics are here: MIDI-Board


credit MIDI IN circuit design: Jeff Mann




  • inverter 74LS04N
  • opto isolator 6N138
  • 3 low current LEDs
  • 1 capacitor 47nF
  • resistors: 3x 2kOhm, 3x 220Ohm, 1x 3,3kOhm, 1x 1kOhm
  • 1 diode 1N4148
  • 2 Midi sockets
  • pin
  • Jumper


The MIDI-Board was designed by Wolfgang Spahn 2010-22.
It is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

Creative Commons License