[sdiy] MIDI phantom power...over 5 pin MIDI connector ?

[Richie Burnett]

Hi Tom,

Thanks for clarifying that you can just change the resistor values to make 
the current right to make MIDI work with 3.3V logic.  I did wonder whether 
you still needed a +5V line just to tie up pin 4 of the MIDI output jack.

Since MIDI is a current loop standard, I should in theory be able to 
implement a MIDI output port by grounding pin 5 of the DIN socket, and 
switching a current-source in the high-side connected to pin 4 of the DIN 
socket then?  That would still meet the standard in terms of an on/off 
modulated 5mA current loop and drive the floating opto-coupler at a MIDI 
input port just fine.  (I wonder if anyone does this?)  I'd imagine that it 
would mess up any product that anticipated the "Electrical Specification 
Diagram" example shown in the MIDI spec and planned to draw power from pin 4 
though?

-Richie,