Raspberry Pi Pico Polyphonic DCO

This repository contains source code, schematics and PCB for a digitally controlled oscillator (DCO) with up to 6 voices which are driven by a Raspberry Pi Pico. It uses PIO to generate a highly accurate frequency which is controlled by USB or serial MIDI. The analog oscillator part is based on the Juno 106 and generates sawtooth and square wave signal with a 10Vpp amplitude. Amplitude compensation is done by a smoothed PWM signal coming from the Pico.

Key features

Digitally controlled analog oscillator using a Raspberry Pi Pico
Up to six voices
Voice stacking
Detuning of voices
Separate gate signal
DIN MIDI serial input
USB MIDI input
MIDI pitch bend
Portamento with adjustable speed

This is how it sounds: Ramp sample Pulse sample Polyphonic sample

I use the DCO in my Polykit-6 polyphonic synthesizer built, see https://www.youtube.com/watch?v=vj-DSh6yfM0 and https://www.youtube.com/watch?v=go1mErOdtsU

Schematics and PCB

Gerber files for the PCB can be found here.

Installation (simple)

Press BOOTSEL button on the Pico while powering it with USB. Copy file build/pico-dco.uf2 onto the USB mass storage device.

Usage

After installing the Pico should register as USB MIDI device. Alternatively serial MIDI input is available. The DCO listens to note on/note off messages on MIDI channel 1. Pitch bend is also supported. Portamento can be enabled by MIDI CC message #65, portamento time can be adjusted by CC message #5.