I'm building a MIDI IN to serial port RX cicruit (for Raspberry Pi, or Arduino, or anything else...) using a 6N138 optoisolator.
But I find many different circuits, I don't know why there are so different, and which one to choose:
Are these correct?
First, this one with a 470 Ohm and 1KOhm resistor http://www.electro-tech-online.com/customimages/2011/02/MIDIINTHRU-1.jpg
Another, with respectively 1KOhm and 3.3KOhm resistor
- The official one on
midi.org, with different resistor values, but not based on 6N138...
Last thing (maybe off topic here): If I want to connect to Raspberry Pi's GPIO's RX, should I use 3.3V for the optoisolator instead of 5V, to prevent breaked with GPIO's RX?