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Topic: MIDI Input - borrowing power... (Read 1 time) previous topic - next topic

WilliamK Govinda

I know this is possible, as I've seen some MIDI Merger devices that does this: how to get some sort of power from a MIDI cable.

http://www.midi.org/techspecs/electrispec.php

http://www.midisolutions.com/faqs.htm

Lets say I want to make a small midi box that has an ATmega8 chip inside, Midi Input and Midi Output. But I want to power the ATmega8 from the Midi cable itself.

How would I approach this? ;-)

Thanks, Wk

daatse

since in the standard MIDI-cables only 3 of the 5 pins ar used
http://www.allpinouts.org/index.php/MIDI
you could use the other 2 as a GRND and VCC
however this might effect your MIDIsignal and for this to work your device at the other end must be connected this way to feed your MIDI device

an other tecnique used for microphones is working with so called "phantom power"
http://en.wikipedia.org/wiki/Phantom_power
however i really doubt if you get that to work

i hope this helps you

rfielding

I'm doing it right now, with Arduino Mini Pro 5v:

IN.5 -> rx
IN.2 -> gnd
IN.4 -> Battery+ (ie: regulated, up to 9v)
IN.4 -> 220Ohm -> vcc (ie: 5v input - not regulated)

OUT.5 -> tx
OUT.4 -> 220Ohm -> vcc
??? OUT.2 -> gnd (not connected to ground, it works though)

I have a MIDI IN, Mini Pro, MIDI OUT.  It's a reprogrammable MIDI filter.  (I use it for automated octave switching and microtonal retuning.)  It works.  I am unsure if I should be connecting tx to OUT.2, or whether I really should pass IN.5 or OUT.5 through 220Ohms.  (IN.4 is 5v that has already passed through a 220Ohm resistor out of the keys controller).

Also note that it's kind of backwards to have the input device supply power, because it's typically the synth that has power; where it might make sense to have unpowered controllers.  I think this explains the mystery of why the MIDI standard circuit attaches OUT.2 to ground, while IN.2 is not connected; scenarios where the device has its own power, so it is optically isolated from IN rather than drawing power off of (IN.5,IN.2).

Yes, I know it's a super old post.  But I am hoping that this gets found in Google searches.

BenKissBox

About the MIDI Solutions system: they use the current loop to charge a power supply within the devices. When you take a look to the list of MIDI interfaces not working correctly with their products, it's rather impressive (it's on their FAQ page)

I do not like at all their systems, I had problems in the past, and it took hours to figure what could be wrong (and finally, it was going to the fact that an external power supply is needed)

Note that if you provide power supply on the free pins of the DIN, your connector is not anymore compliant with MMA specifications. But as long as you do not make a sellable product and you know that your device is not fully compliant with MMA standard, I think it's OK.

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