What do you do if you want the convenience of MIDI but the warm tones of analog synths? Build a MIDI to CV converter, of course! In this project, you'll use a QT Py RP2040 running CircuitPython with an MCP4725 DAC to convert MIDI messages to a gate output and 1V/oct output. 

The build is housed in a snazzy 3D printed skull adorned enclosure. The output jacks are located in the skull's eyes.

The CircuitPython code converts MIDI NoteOn and NoteOff messages to gate out and 1V/oct signals that are sent through the two mono audio jacks. This lets you play your CV controlled synths with a MIDI keyboard or a MIDI song file from your DAW.

The MCP4725 DAC is a digital to analog converter and outputs the voltages to correspond with the expected 1V/oct value.

What is 1V/oct?

1V/oct is a standard for controlling pitch in modular synthesis. A volt is divided to correspond with the twelve pitches in western music. For example, 0.333V is pitch E-2 and 0.917V is pitch B-2. When the voltage is increased by 1V, the octave increases by 1. For example, 1.333V is pitch E-3 (an increase of 1V and 1 octave) and 2.917V is pitch B-4 (an increase of 2V and 2 octaves).

However, these pitches are approximate and depend on a variety of factors, such as your oscillator's tuning and any electrical interference. But that's half the fun of synthesis!

Prerequisite Guides


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Vertical Breadboard-Friendly 3.5mm Mono Headphone Jack with audio cable plugged in
Pipe audio in or out of your project with this very handy breadboard-friendly audio jack. It's a mono jack with a disconnect pin so you'll get a ground sleeve pin, a left tip...
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Angled shot of MCP4725 Breakout Board - 12-Bit DAC w/I2C Interface.
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Silicone Cover Stranded-Core Wire - 30AWG in Various Colors laid out beside each other.
Silicone-sheathing wire is super-flexible and soft, and its also strong! Able to handle up to 200°C and up to 600V, it will do when PVC covered wire wimps out. We like this wire...
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Angled shot of coiled pink and purple USB cable with USB A and USB C connectors.
This cable is not only super-fashionable, with a woven pink and purple Blinka-like pattern, it's also made for USB C for our modernized breakout boards, Feathers, and...
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1 x Short Break-away Male Header
36-pin 0.1" Short Break-away Male Header - Pack of 10
1 x Short Female Header
36-pin 0.1" Short Female Header - Pack of 5
1 x M2.5 screws
M2.5 screws and stand-offs

This guide was first published on Aug 02, 2022. It was last updated on Jul 29, 2022.

This page (Overview) was last updated on Jul 29, 2022.

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