[sdiy] MIDI activity LED circuitry

[Rainer Buchty]

>If such a circuit is dependant on the MIDI ports' own circuitry I can 
>try to provide more information about that, but perhaps it's just a 
>matter of adding some new circuitry to the existing inputs and outputs?

For the output ports I'd go right before the output driver (typically 
single transistor or 7406) and add another driver for the LED; 
input-wise similarly after the opto coupler.

Rainer