qtpy_synth

What is it?

This is a partially-assembled PCB with the features:

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

The completely assembled SMD sections of the board are:

1. Audio output circuit
2. TRS MIDI input circuit
3. Capsense touch circuit

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

1. QTPy RP2040
2. 0.96" I2C OLED display (w/ pins in Gnd/Vcc/SCL/SDA order)
3. Two 10k potentiometers, 9mm (example pots and knobs)
4. One tact switch, 6mm (example switch)
5. Headers and sockets to mount QTPy & display, to taste
6. This male & female header kit looks pretty good,
7. as I prefer to put female headers on the PCB and male headers on the QTPy and OLED display.
8. You may need to trim down your headers to be the right size
9. Feet. I like M2.5 nylon standoffs (e.g. M2.5 standoff asst kit)
10. but feel free to do what you like, including making an enclosure!

The recommended order of operations for building is:

1. Solder down headers for QTPY and display, make sure they're straight
2. Solder down pots and switch
3. Attach feet and knobs
4. 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:

1. hwtest - test out the hardware with a simple synth
2. simpletouchsynth - play with filters using touch sensors
3. wavesynth - larger general two-osc synth that can also do wavetables
4. early video demo: "Wavetable synth w/ CircuitPython synthio on QTPy RP2040"
5. 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.