[sdiy] MIDI specifications

[Magnus Danielson]

From: Ingo Debus <debus at cityweb.de>
Subject: Re: [sdiy] MIDI specifications
Date: Fri, 18 Apr 2003 15:47:57 +0200

> Magnus Danielson wrote:
> >>what would this do or prevent? it seems to work as it is.. a small wooden
> >>teabox with some holes for the midi ports i've just soldered wires from the
> >>input-pins to each output pin.
> > 
> > 
> >>From the output you have a current, it's going to drive 5 inputs now, which
> > means that the opto-coupler runs at the fifth of the current it is supposed to
> > run at, meaning less emitted signal and all that. If it works it works, but you
> > have just moved from one case of a limit into another. Also, all of a sudden you
> > want to run another pair of boxes in the same time, so you hang them in too...
> 
> The biggest problem here seems to me is that there are now several 
> LEDs in parallel with a common current limiting resistor. Those with 
> just a slightly higher voltage drop won't light up well.

Yeah, I didn't even think of it, but current sharing between diodes is a royal
pain in the body-chair-interface if you don't actually do control-loops to
handle it (there is a set of good components from Unitrode to do this for
things like parallelled power-supplies). I've done the exercise with slightly
higher currents...

> > By using a single chip and a small handfull resistors and a opto-coupler, you
> > have built yourself a propper MIDI-splitter. My point is that it isn't as far
> > away, so why not do it properly? As it is now you survive over the weekend, but
> > is it the long-time solution?
> 
> Well, it would need a power supply...

Yes, but a small wall-wart would do it.

Cheers,
Magnus