ATtiny85 MIDI IN using SoftwareSerial - Is it possible?
I have done tests with a normal Arduino with software serial and missed quite a bit of messages, so I would advice to use hardware serial's instead.

For MIDI Out probably it works, but for MIDI In I have bad experiences. Especially when it comes to many messages, like aftertouch/pitch bend etc.

Also, I tried some optocouplers which didn't work well (like 6N137). I now use H11L1 optocouplers (they are white compared to most black ICs) and work perfectly.

You already checked the clean note on/note off ... are you sure it doesn't send active messages?

Below the schematic as I use it.. It does not matter if an STM32 or Arduino is used. Actually I haven't checked if H11L1 are 3.3V or 5V but they seem to work on both.







simulate this circuit &ndash; Schematic created using CircuitLab