I'm trying to connect an older PC with a DA-15 (Gameport/MIDI) to a Raspberry Pi using MT32Pi.

The Gameport/MIDI is +5v and the RPi is +3.3v so I'm using an optocoupler and voltage divider.

Does this look correct or could it even be simplified?

Thanks so much for any help!


  • \$\begingroup\$ Do you want to make one real MIDI in port and one real MIDI out port, or simply connect the two things together? Also, you can't power the optoisolator detector side with a resistor divider. Either power it directly with 3.3V, or power it directly with 5V and do a proper level translation from 5V to 3.3V. \$\endgroup\$
    – Justme
    Dec 28, 2021 at 22:59
  • \$\begingroup\$ Sorry, I should have clarified ... I'm just looking to connect them together so ignore the MIDI connector in the middle. Also, why can't I power the coupler with the resistor divider? \$\endgroup\$
    – SofaKng
    Dec 29, 2021 at 0:48

1 Answer 1


You do not need any of that stuff. Just do voltage conversion from 5V to 3.3V.

Having said that, I noticed that my Aztech Galaxy Basic 16 soundcard midi output from joystick port pin12 doesn't tolerate any load, so my 2k and 1k resistor voltage divider didn't work. I added 7404 for buffer (7400 and many other works too). So I would leave that 7400 in your diagram and then I would do voltage divider with 2 resistors.

  • \$\begingroup\$ The LS TTL output high is very weak. About 0.4mA at 3.4V. It really can't drive a voltage divider. Your sound card may have an open drain output with weak pull-up, which was common for that era. \$\endgroup\$
    – Justme
    Aug 15, 2023 at 15:24

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