==== Pat ====
Normally MIDI uses 5V, but since it is a current loop it can also be run at 3.3V.
MIDI spec says 5 mA of current in the current loop.
doc/pi.midi.jpq shows a picture of a MIDI breakout board with MIDI IN and OUT DIN connectors. The schematic is doc/pi.midi.schematic.jpg.
MIDI OUT is connected to GPIO26 using the green wire. Green is our color convention for PI TX and HOST RX.
MIDI IN is not used in these examples. It would be connected to PI RX and HOST TX. MIDI IN is routed through the 6N138 optoisolator.
The current circuit uses 220 Ohm resistors as is typical of the MIDI spec. It would be safer to lower the value of the resistor by 3.3V/5.0V to keep the current constant with 3.3V.
An inexpensive USB IN-OUT MIDI cable can be used to connect to a laptop. I connected this to my macbook, and was able to play music using GarageBand. I also used MidiMonitor to show the midi notes as they were being sent.
Author: Pat Hanrahan email@example.com Date: Feb 18, 2019, Updated Mar 9, 2021
===== Phil ====
Sample code to control a KORG volca keys or volca beats from the Pi. Connect the midi data line to GPIO pin 25 (through a 220Ohm resistor) and the current line to 5V through a 220Ohm resistor.
- Makefile: make on its own will make midi-beat (drums on the drum kit) make install will make and install midi-beat
make install midi-lamb will make and install midi-lamb
MIDI-in pins: white wire to 220ohm resistor to 5V on Pi red wire to 220ohm resistor to pin BCM/GPIO 25
For PulseView logic analyzer with DreamSourceLab DSLogic Pro: a. Ground goes to Pi ground b. Signal pin goes to red MIDI (pin 25 on Pi) c. Set voltage range on PulseView to 1.6V for 0/1 d. Set UART as decoder, with 31250 baud rate (8n1) e. In UART, choose "Stack Decoder" and select MIDI
Actual pinout of MIDI connector:
silver (unshielded), gnd when using logic analyzer _____ .-' '-. red .' o '. white (signal)/ o o \ (5V) ; ; yellow | o o | black (no conn) ; ; (no conn) \ / '. .' '-._____.-'