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
- Frequency modulation (FM)
- 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, 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.
Detuning, stacking and FM
The build-in analog-to-digital converter can be used to modulate these parameters. You can add an external control voltage (0-3.3V) to that input pins. These features can be disabled by commenting (//) the following lines:
#define USE_ADC_STACK_VOICES // gpio 28 (adc 2)
#define USE_ADC_DETUNE // gpio 27 (adc 1)
#define USE_ADC_FM // gpio 26 (adc 0)
References
https://blog.thea.codes/the-design-of-the-juno-dco/
https://electricdruid.net/roland-juno-dcos/
https://www.youtube.com/watch?v=yYnQYF_Xa8g
https://github.com/raspberrypi/pico-examples/tree/master/pio/pwm
https://github.com/raspberrypi/pico-examples/tree/master/pio/pio_blink
https://github.com/raspberrypi/pico-examples/tree/master/pwm/hello_pwm
https://qiita.com/jamjam/items/f2fdd5c072ff348fd809
https://github.com/infovore/pico-example-midi
https://learn.sparkfun.com/tutorials/midi-tutorial/all
http://www.music-software-development.com/midi-tutorial.html