Duppa I2C MIDI Controller PCB Design

By Kevin on April 27, 2025

This is the design for a simple carrier PCB for a Waveshare Zero format microcontroller and a Duppa small LED Ring. It is essentially a PCB version of Duppa I2C MIDI Controller – Part 4.

Warning! I strongly recommend using old or second hand equipment for your experiments. I am not responsible for any damage to expensive instruments!

If you are new to microcontrollers, see the Getting Started pages.

The Circuit

This connects a Waveshare Zero format board to a MIDI IN and OUT interface and a potentiometer. There is a header required to connect to the Duppa Small LED ring.

The following IO pins are used:

Physical Pin	GPIO: C3, S3, RP2040	Function
1	Power	5V
2	Ground	GND
3	Power	3V3
4	GP0, GP1, A3	Potentiometer
13	GP9, GP10, GP5	LED SCL
14	GP10, GP11, GP4	LED SDA
17	GP20, RX, GP1	MIDI RX
18	GP21, TX, GP0	MIDI TX

For the RP2040 this is using I2C0 and UART0.

PCB Design

I've actually opted not to include MIDI IN functionality in order to keep within a minimal PCB footprint. I'm aiming to have it occupy essentially the same space as one of the small Duppa LED rings itself. I'm also only support MIDI OUT via a TRS jack.

But I have attempted to ensure that both the Waveshare USB socket and TRS socket will protrude enough to be brought out to the edge of a case.

I've included a 2.54mm pitch set of header pads that I plan to solder a connecting wire to for the Duppa ring.

Closing Thoughts

I was in two minds about including MIDI IN. It is nice to be able to use this to merge into an existing MIDI stream, but then I also considered that it would probably be used just as a controller in most cases, so went with the small PCB footprint.

I also considered the four control options I've experimented with so far. In the end I decided I still liked having an absolute-value potentiometer for a MIDI Controller like this over either a rotary encoder or an endless potentiometer, so that is what I've used.

Kevin