What is it?

This is a partially-assembled PCB with the features:

• Mono audio output circuit, converting PWM to audio, as per RP2040 design guidelines
• Optoisolated MIDI Input via MIDI TRS-A 3.5mm jack
• Two pots for controlling parameters
• One switch for controlling parameters
• Four capsense touch buttons for synth triggering
• USB MIDI in/out of course too

The completely assembled SMD sections of the board are:

• Audio output circuit
• TRS MIDI input circuit
• Capsense touch circuit

The parts you need to add (and solder down) are:

• QTPy RP2040
• 0.96" I2C OLED display (w/ pins in Gnd/Vcc/SCL/SDA order)
• Two 10k potentiometers, 9mm (example pots and knobs)
• One tact switch, 6mm (example switch)
• Headers and sockets to mount QTPy & display, to taste
• This male & female header kit looks pretty good, as I prefer to put female headers on the PCB and male headers on the QTPy and OLED display. You may need to trim down your headers to be the right size
• Feet. I like M2.5 nylon standoffs (e.g. M2.5 standoff asst kit) but feel free to do what you like, including making an enclosure!

The recommended order of operations for building is:

• Solder down headers for QTPY and display, make sure they're straight
• Solder down pots and switch
• Attach feet and knobs
• Plug in QTPy and display

Why did you make it?

I wanted a quick and easy platform to test out CircuitPython's synthio and also play with Mozzi.

You can find some example code made for this board in the qtpy_synth repo, including: Some programs written specifically for this board:

• hwtest - test out the hardware with a simple synth

• simpletouchsynth - play with filters using touch sensors

• wavesynth - larger general two-osc synth that can also do wavetables

• early video demo: "Wavetable synth w/ CircuitPython synthio on QTPy RP2040"
• another demo: "More Wavetable synth w/ CircuitPython synthio on QTPy RP2040"

Additionally, you can adapt any of the code snippets at circuitpython-synthio-tricks.

What makes it special?

There aren't that many RP2040-based boards that have a simple PWM audio output. This board does that.