Plink is an open-source, velocity-sensitive USB MIDI keyboard built around the Raspberry Pi Pico (RP2040) and magnetic Hall-effect key switches.

Each of the 16 keys sits over an SS49E linear Hall sensor. A CD74HC4067 analog mux feeds all 16 sensors into a single ADC pin. The firmware times how long each key takes to travel between two points in its stroke and turns that into MIDI velocity, just like a real piano action.

Features

- Velocity-sensitive Hall-effect keys (contactless, no wear)

- Plug-and-play USB MIDI: no drivers on Windows, macOS or Linux

- Automatic per-key calibration at power-up

- One WS2812 NeoPixel per key, driven by the RP2040's PIO

- ±24 semitone transpose from two buttons

- Firmware in C on the Pico SDK + TinyUSB, with host-side unit tests and CI

Bill of materials

- 1× Raspberry Pi Pico

- 1× CD74HC4067 16-channel analog mux

- 16× Hall-effect linear switches

- 16× SS49E linear Hall sensors

- 16× WS2812 NeoPixels

- 2× momentary push buttons

The PCB was designed in KiCad, and the enclosure is modeled in FreeCAD. Firmware, schematics and design files are all on GitHub:

https://github.com/Logan-Fouts/Plink

Status: the firmware is working on a breadboard build, and this PCB is the v1.0 hardware.