This entry is part 1 of 2 in the series Raspberry Pi Pico as MIDI to CV converter
I’ve been toying with the idea of building a MIDI to CV converter for at least a decade. Now I’ve finally had a go using MicroPython on the Raspberry Pi Pico.
Here’s how I managed to control my Moog Werkstatt-01 over MIDI using the Pico, a handful of components and a MCP4725 12-bit DAC:
The Hardware
BOM
- Raspberry Pi Pico
- HC11L optocoupler
- 220Ω Resistor
- 470Ω Resistor
- small signal diode (eg 1N914)
- MCP4725 module
Circuit Diagram
The Code
The code is written in Micropython. Its only external dependency is the SimpleMIDIDecoder class by @diyelectromusic. You can download the latest version on GitHub here: SimpleMIDIDecoder.py.
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# MIDI to CV converter for Raspberry Pi Pico and MCP4725 DAC by @AxWax | |
# | |
# Demo: https://www.youtube.com/watch?v=aGfQHL1jU4I | |
# | |
# This is heavily based on and requires | |
# the SimpleMIDIDecoder library by @diyelectromusic, which can be found at | |
# https://diyelectromusic.wordpress.com/2021/06/13/raspberry-pi-pico-midi-channel-router/ | |
# | |
# | |
# Wiring: | |
# serial midi input on GP1 (UART0 RX) | |
# gate output: GP17 | |
# | |
# MCP4725 Pico | |
# GND GND | |
# VCC VBUS (5V) | |
# SDA GP6 | |
# SCL GP7 | |
# VOUT is the CV output | |
import machine | |
import time | |
import ustruct | |
import SimpleMIDIDecoder | |
# which MIDI note number corresponds to 0V CV | |
lowest_note = 40; | |
# create gate pin | |
gate = machine.Pin(17, machine.Pin.OUT) | |
gate.value(0) | |
#create an I2C bus | |
sda=machine.Pin(6) | |
scl=machine.Pin(7) | |
i2c = machine.I2C(1, scl=scl, sda=sda, freq=400000) | |
# calculate 1mV: steps / max V / 1000 | |
mv = 4096 / 5.1 / 1000 | |
# calculate mV per semitone | |
semitone = 83.33 * mv | |
# DAC function | |
def writeToDac(value): | |
buf=bytearray(2) | |
buf[0]=(value >> 8) & 0xFF | |
buf[1]=value & 0xFF | |
i2c.writeto(0x62,buf) | |
# Initialise the serial MIDI handling | |
uart = machine.UART(0,31250) | |
# MIDI callback routines | |
def doMidiNoteOn(ch, cmd, note, vel): | |
global semitone | |
writeToDac(int((note–lowest_note)*semitone)) | |
gate.value(1) | |
def doMidiNoteOff(ch, cmd, note, vel): | |
global semitone | |
gate.value(0) | |
# initialise MIDI decoder and set up callbacks | |
md = SimpleMIDIDecoder.SimpleMIDIDecoder() | |
md.cbNoteOn (doMidiNoteOn) | |
md.cbNoteOff (doMidiNoteOff) | |
# the loop | |
while True: | |
# Check for MIDI messages | |
if (uart.any()): | |
md.read(uart.read(1)[0]) |
- Raspberry Pi Pico as MIDI to CV converter
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