Cheap DIY USB MIDI to CV

uMIDI2CVliteCable

How do you make a USB MIDI to CV interface?

This one is simple and does not require any expensive Teensy’s or STM32.

It runs on the ATtiny85 using V-USB.

The ATtiny is programmed with the Micronucleus bootloader and is firmware upgradeable incircuit.

DigisparkMIDI2CV

If you don’t want to build the circuit above, a cheap chinese Trinket does the job.

s-l300

uMIDI2CVlite

It can be built into an analog synth like the Korg Monotron to give it USB MIDI.

IMG_20171111_153755

You also need the DigiMIDI library found here:

https://github.com/heartscrytech/DigisparkMIDI

To be able to receive MIDI from the host, the file DigiMIDI.h requires some modification.

Add this to the function usbFunctionWriteOut:

void usbFunctionWriteOut(uchar * data, uchar len) {

uint8_t note=data[2]; //Get note for key on/off
if (note<36) note=36; //If note is lower than C2 set it to C2
note=note-36; //Subtract 36 to get into CV range
if (note>60) note=60; //If note is higher than C7 set it to C7
if (data[1] == 0x90) { //If note on
digitalWrite(5, HIGH); //Set Gate HIGH
OCR1A = note<<2; //Multiply note by 4 to set the voltage (1v/octave)
}
if (data[1] == 0x80) { //If note off
digitalWrite(5, LOW); //Set Gate LOW
OCR1A = note<<2; //Multiply note by 4 to set the voltage (1v/octave)
}

}

And this is the MIDI2CV.INO sketch:

#include <DigiMIDI.h>

DigiMIDIDevice midi;

void setup() {
pinMode(1,OUTPUT); //Pitch is output
pinMode(5, OUTPUT); //Gate is output
//Setup Timer1 to do PWM DAC for Pitch
TCCR1 = _BV(PWM1A) | _BV(COM1A1) | _BV(CS10);
GTCCR = 0;
OCR1C = 239;
OCR1A = 0; //Set initial Pitch to C2
digitalWrite(5,LOW); //Set initial Gate to LOW;
}

void loop() {
midi.update(); //Check if any MIDI data is received
}

8-bits is actually a to low resolution for the pitch but a trick makes it work.

The CV range is set to 0-239 instead of 255 and that makes each seminote exactly 4 steps.

Thats it, very simple and cheap.

If you have no clue about programming and soldering skills only you can buy the preprogrammed Digispark board here:

The DIY preprogrammed MIDI2CV Digispark is available at: http://www.dspsynth.eu

My work on these free synthesizers is based on donations from people.
If you find the code useful, please consider a donation to keep future developments open source.