Duppa I2C MIDI Controller PCB Build Guide

By Kevin on April 27, 2025

Here are the build notes for my Duppa I2C MIDI Controller PCB.

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.

Bill of Materials

Duppa I2C MIDI Controller PCB (GitHub link below)
Waveshare Zero format dev board
1x Duppa Small RGB LED Ring
10KΩ potentiometer
5-pin plug and lead (see photo).
1x 100nF ceramic capacitor
Optional: 1x10Ω, 1x33Ω resistor
Optional: 1x 3.5mm stereo TRS socket - PCB mount (see footprint and photos)
Optional: 2x 9-way header sockets. Ideally low-profile, PH5.0 sockets.

There are a range of possibilities for the potentiometer, so one has to consider if mountings are required or if a knob will be used. These are some of the pots I could have used:

I used the one with a nut in the end and plan to add a knob at some point.

On that lead... The Duppa ring is described as requiring a "5-way Molex Picoblade, 1.25mm pitch" connector. The lead I ended up with was described on an online, overseas marketplace, as "JST 1.25mm" which I'm not sure is strictly a thing, but that is what worked for me.

Build Steps

Taking a typical "low to high" soldering approach, this is the suggested order of assembly:

Resistors and diode.
Disc capacitors.
TRS socket (if used).
If using headers for the devboard, now is a good time to solder those.
Potentiometer.
Duppa connector cable.

Be sure to get the connector cable the right way round. For the colouring of the cable above, and orientation of the pins, the I2C connectors ended up being the red and black ones for me. More about that in a moment.

Here are some build photos.

The cable has to be cut and then positioned to correctly align with the positions of the wires on the Duppa connector. The following shows which wires align to which solder pads and the position in the connector.

Once all soldering is complete, I used 8x 10mm M3 spacers as shown below.

I'm planning on designing an enclosure that the above posts will slot into. You may need different senses and sizes of spacers depending on your final arrangements.

Testing

I recommend performing the general tests described here: PCBs.

Note that the LED ring is configured using solder jumpers as described previously, for S1, S5 and to use pull-ups, as shown below.

PCB Errata

There are the following issues with this PCB:

None at this time.

Enhancements:

The schematic already supports MIDI IN in addition to MIDI OUT, so at some point I could add that too.

Find it on GitHub here.

Sample Applications

This is designed for use with my Duppa I2C MIDI Controller – Part 4. The Arduino code for that works directly when used with a Waveshare Zero RP2040 with the following configuration:

#define WAVESHARE_RP2040

#define MIDI_USB
#define MIDI_SER

#define LED_PER_CC
#define LED_SCALE_TO_RING

#define CC_POTENTIOMETER
#define PIN_ALG A3
#define MAX_POT_VALUE 1023

The full code is available on Github here.