[sdiy] Midi powered?

[Colin f]

> I noticed that some Midi devices are able to power small external
> devices while others can't.

> I digged through the midi specification, but couldn't find any
> reference about this. Is this an undocumented feature adopted by some
> manufacturers?

Sort of.
The typical midi output has 3 connections - +5v, 0v and data.
Both the data and +5v lines are usually protected by small (~200 ohm)
resistors.
So, you can draw a small amount of current from the +5v line to power
something, but the more you draw, the more voltage drop you will get due
to the resistor.
You may find that some devices have larger resistors on the +5v line, so
line powered devices wont get enough voltage.
Modern devices can be powered easily from the midi line, as they draw tiny
amounts of current, but older devices may be marginal.

Colin f



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