Powering Arduino with MIDI keyboard

Thread Starter

Green Bean

Joined Mar 31, 2017
I would like to connect my Arduino to a MIDI keyboard. The typical way seems to be to use an optocoupler and power the keyboard and arduino separately. This is fine, but the only optocouplers I have are 4n35s, which I think are not fit for the job.

Is there a way to use a 4n35 for this application? I would rather use extra parts that I already may have than order a new part and wait for shipping.

I'm guessing no, so now my idea is to use the keyboard to power the Arduino. This would eliminate the need for an optocoupler entirely, and I think it would be more convenient than using two power supplies. Ok, so I measure voltage at what I think is + and - (I think pin 2 being + and 3 being -, but I am away now) on the MIDI out port and I get 5.11 V. So the only way to power the Arduino off this is to plug that directly into the +5V pin of the Arduino, which I know is not reccomended, but I did it anyway (after having unplugged the Arduino from my computer, of course). Everything seemed to power up ok, but the LED on Arduino pin 13 (it's an Uno BTW) did not dim as it should have (the program would not have turned it on). Now, normally when I boot up the Arduino, the light turns on briefly, but then dims, so I'm wondering if it keeps rebooting. The only explanation I can think of for this is that what I think is the + pin is actually the MIDI signal, and the 5.11V reading is just my meter getting confused. But I have no clue. Any thoughts?


Joined Feb 20, 2016
I don't think you will have power available on the MIDI connector, just the signals. I may be amiss there but I think you will need to feed power from the keyboard separately.


Joined Jul 5, 2008
MIDI keyboard Is nice but it really tells us nothing a link to what your using is way better then us shooting in the dark here.


Joined Feb 20, 2016
Looking at the MIDI info, there is no +5V on the connector. It is +5V via a 220R resistor. So you cannot power the Arduino via the MIDI port.