[sdiy] Midi powered?

[Colin f]

> Not sure about the 3 connection MIDI hookup.  Never
> seen that before.  But without digging into the MIDI
> spec.....

MIDI outputs have 3 connections.
MIDI inputs have 2 connections.
The ground connection is not made at the input to prevent ground loops.
But it must be present at the output socket otherwise your MIDI cable will
be unshielded.

It might be worth pointing out here that I have built and sold a dozen or
so midi to din sync convertors that draw their power from the midi bus,
and they all worked.

Problems occur where the MIDI output, instead of having a +5v connection
to the input optoisolator LED anode (MIDI pin 4), and an open-collector
pull down on the opto LED cathode (pin 5), has the anode line driven high
with the data (inverted), and the other line tied to 0v.
This gives you no +5v supply to play with. It does turn the LED on.
I've only ever seen this once, in a real p.o.s. MIDI interface.

Colin f




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