I'm trying to do my own MIDI input board from the tutorials. Is there something special about a 6n139 optocoupler I need to buy special, or will mostly anyone work? I have dpc-817c optocouplers.
Yes, there's something special. Only faster optocouplers work well. Many slow ones don't work at all. Or if they do work, you get a pretty terrible copy of the original signal which the hardware serial can usually sort out, but at the expense of using all all the design margin you'd normally have for rejecting noise, interference, timing issues, etc.
Ok, I finally got my rat's nets of wires on the breadboard. I tested. After a couple of hours of light traffic over the midi, it appears to work as a drop in replacement using the exact same values with the resistors too.
The thing about electricity is I never know when I've done it wrong until I small something or see smoke.