MIDI troubleshooting help, pliz

mpark

I have a little MIDI OUT interface wired as shown in the attachment. It works fine sending to either of two MIDI keyboards, but when I try to send to a MIDI-USB box, nada. There's a little LED that's supposed to light up when the box receives data but it stays dark (I have seen it light up when I hooked the box up to one of the aforementioned keyboards).

I'm using the pcfullduplexserial4fc object to transmit. I've tried OCTX and NOMODE and have connected the high side of the MIDI circuit to 5V and 3.3V. As I said, I can make it talk to two keyboards, just not the MIDI-USB box for some reason. Any ideas what that reason might be?

Ariba

Hello mpark

Normally the MIDI IN has a 220R and a LED (from the optocoupler) between the 2 MIDI IN pins. If the MIDI-OUT sends a LOW the current must be 5mA. On HIGH no current should flow.
If the LED needs 1.7V then the current of your circuit is (5V - 1.7V) / 660R = 5mA for a LOW. But for a HIGH there may be a little current because of the protection diode to 3.3V of the Propeller.

Have you tried this circuit? :

cheers
Andy

mpark

That did the trick! Thank you, Andy, for explaining in a way that I could understand!