I'm having trouble getting midi input working. I've built the MIDI input circuit using a Sharp PC900V, so basically keeping as close to the official spec as possible. I've been able to verify that the optoisolator is working fine; I've built a test circuit with a LED connected to the output of the optoisolator, when I power up the circuit the LED comes on and if I apply a couple volts across the emitter it shuts off. So the circuit itself seems ok.
However, when I connect a midi device to the input I get no luck. I've tried MIDI outputs from two difference devices; a Oxygen 8 keyboard and a old emagic mt4. Neither out which give me anything . If I put a LED and a ~220 Ω resistor between pins 2 & 5 of the MIDI input I can faintly see it glow as events are sent, so I have to assume that everything looks good there and it's providing enough power for the LED in the optoisolator. However if I put a LED & resistor between the output of the optoisolator and ground I get no flashing at all, it just stays on, which is curious.
When trying to test the MIDI input I've got got the Arduino on it's own power supply, not USB power. And when uploading to the Arduino I've found I need to disconnect it from any MIDI device, or the upload will fail.
Now for the strange part. The LED hard-wired into pin 13 has done some strange things when everything is connected and powered up. I'm using very simple test programs, but what happens is the LED does the initialization blink, then goes on, and stays on, until i disconnect the input from the serial rx (pin 0). Could this be a short somewhere?
Any help or guidance would be great, I've been stuck on this for far too many evenings!