Ableton Forum

Here's a thought that just occured to me... why can't midi cables be used to supply current to devices by applying a DC offset voltage to the control lines? It must've been tried before, eh? Just thinking aloud here and there's probably a perfectly good reason like current variation why it hasn't been done...

Any ideas?

The wires inside the cables are very thin. They would not be able to work with much power. This being said there is no reason that a couple of the wires in the cable could not be made a little heaver. I have used a balanced patch cable to send midi data if that is any inspiration

Lemme see, the wallwart for my synth is 12V DC / 500mA. And what's Midi 5V/0V, I guess current is negligible? So run everything at 24V DC and that should provide enough overhead...

Just want to get rid of my damn wallwart!

you raising a good point, this is been done in other cases, like intercom systems from clearcom, they send 12volt over the audio signal line, for the call function...

the dangerous thing is, that if you cross connect to another audio input, not being a clearcom system you can blow the inputs.
(did happened to many people using those systems)

so technically it is possible to send a certain amount of power over a data line at the same time, but it can be dangerous...

that said, i am not aware that in our days anything works with the 5 pol DIN connex except midi in audio equipment, but when midi was developed and they decided to use a 5 pol DIN socket, several other audio connections used DIN, maybe that is why they did not do it, in order to avoid damage in case of a wrong connection by a user??

about the cable, in 5 pol DIN you can send easy 12volt with around 1000mA or even a bit more which would be sufficient to power most standard midi devices.

i mean usb carries what? i think 3.3volt with a few mA or am i wrong here?

USB supplies 5V on the bus, but not enough current to power anything with a pile of LEDs on it. Not enough for an APC-40 for example.

Yeah, the only other thing with 5-pin DIN is my old turntable...

Hmmm... would be interesting to check out further...

USB is 5V at 500mA.

the wires aren't too thin. phone wires, for example carry a 48V signal, low current.

you can do whatever you want with a midi cable, make your own devices that are powered over midi. there are unused pins
http://www.interfacebus.com/PC_MIDI_Pinout.html

interesting idea, but midi should just die.

edit - here's a chart showing how much power you can send over various gauges of wire. my guess is that midi wires are around AWG28.

Show me the chart, show me the chart.

Agreed MIDI should just die, but my Waldorf synth shouldn't so am thinking of neat ways to make it more convenient for the future... Just pipe dreams at the moment, but I find it interesting to think about...

there already is a midi power protocol, but it doesn't carry much juice. i've got a midi splitter box that's powered by midi. do a google for it - it does exist but it's just not used much...

8O wrote:Show me the chart, show me the chart.

sorry man, didn't see your post, been cleaning the house and reading the forum just to avoid work... kinda like I do all week at work.

anyway... THE CHART
http://www.powerstream.com/Wire_Size.htm



Clearscreen - I googled a bit for power over midi but can't find anything.

we're stuck with midi just like some people are still stuck with CV.

One of the requirements of the MIDI standard is that input connections be opto-isolated.

This was to avoid issue like ground noise and the like. The electrical systems of 2 midi devices never actually touch.

Tone Deft wrote:Clearscreen - I googled a bit for power over midi but can't find anything.

http://www.midisolutions.com/prodpwr.htm
here's a power supply designed for powering other midi devices over the midi cable - see the midi in and thru? if i get a chance i'll google a bit more later...

bencodec wrote:One of the requirements of the MIDI standard is that input connections be opto-isolated.

This was to avoid issue like ground noise and the like. The electrical systems of 2 midi devices never actually touch.

Yup, you're right, and that would render my idea useless. But Tone Deft's pin wiring link above shows two free pins which could be used independently to supply power. Hmmmm... I like it as an idea, but am not sure if I want to start modding a perfectly working Ultralite to find it out if I can use the Firewire power over MIDI cable...

nice idea btw.

the Ultralite is 9V in and surely draws more current than you'd want to stress your firewire port with.

you'd have better luck running it off of a few 9V batteries wired in parallel, no mods to the device required. the more batteries you add (in parallel) the longer it'll run.

cool thread! just tagging on...

There are a few devices that do this with special MIDI cables. I think Rocktron might be one. Hosa make cables that work with it.

http://www.samash.com/webapp/wcs/stores ... rySA182946

I'm not sure why they didn't just use the existing pins though.