picotestsynth

A simple Raspberry Pi Pico RP2040 or Pico 2 RP2350-based synth to experiment with synthio and Mozzi.

pico_test_synth2

pico_test_synth, the original

video demo

** Available on Tindie **

Features

• PCM5102 I2S DAC footprint for high-quality stereo audio out
• Optoisolated MIDI Input via MIDI TRS-A 3.5mm jack
• MIDI output via MIDI TRS-A 3.5mm jack
• Two pots for controlling parameters
• One switch for controlling parameters
• 16 capsense touch buttons for synth triggering
• USB MIDI in/out of course too
• (NOTE: the pico_test_synth1 PCB will NOT work with the Pico2, since its RP2350 chip has a hardware error)

pico_test_synth2 vs pico_test_synth

• Both use the same components
• Both run the same code
• Both fit in the same enclosure
• pico_test_synth2 drawn in Kicad; pico_test_synth drawn in Eagle
• pico_test_synth2 has square buttons; pico_test_synth has round buttons
• pico_test_synth2 can work with Pico 2 and Pico
• pico_test_synth can only work with Pico1

Software

Programs written for qtpy_synth will work with this board too with minimal changes.

Some programs written specifically for this board:

• TBish - a TB303-like synth demo (video demo)
• monosynth1 - a full Moog-like monosynth written in Arduino & Mozzi
• hwtest - test out the hardware with a simple synth (video demo)
• wavesynth - port of wavesynth for qtpy_synth board with some improvements

See also:

• CircuitPython Synthio Tricks
  • Contains many other synthio examples that can work with this synth with minimal changes
• Synthio Tutorial
  • a getting-started guide for synthio ending with some full synthesiser voices

Enclosure

As seen in the photos, there is a simple 3d-printable enclosure available on Printables. It's fast to print and you can snap the PCB in to quickly get started, or use M2.5 screws and nuts to secure the PCB more permanently.

Pins used

The board uses all of the Raspberry Pi Pico pins:

• board.GP28 - middle button
• board.GP27 - right knob
• board.GP26 - left knob
• board.GP22 - I2S data
• board.GP21 - I2S LR clock
• board.GP20 - I2S bit clock
• board.GP19 - I2C SCL for OLED display
• board.GP18 - I2C SDA for OLED display
• board.GP17 - TRS UART MIDI in
• board.GP16 - TRS UART MIDI out
• board.GP15..board.GP0 -- touch pads 1-16

For more details see hwtest/code.py.

Schematics

pico_test_synth2

pico_test_synth, original