HexBoard MIDI controller strikes a chord with RP2040

Musical instruments are dependent on physics and maths for their sounds. A guitar string changes pitch when its physical properties change, be that string thickness, tension, or length. A note from a saxophone, or any wind instrument, changes according to the length of the instrument that the air is vibrating through. Any physical instrument needs to have some physical property that the player must interact with in order to play music, and this naturally limits who can play, and what can be played.

The HexBoard has 140 individual mechanical switches, each with a 3D-printed keycap lit by an addressable RGB LED; the unusual keyboard gives rise to unique chord shapes and melodic ideas

At least, that’s how it always was. With MIDI and computers, this no longer has to be true. The instrument that you play is nothing more than an input device, like a keyboard and a mouse, and as such, it can be any shape or size that the maker wants. In this case, maker Jared DeCook has chosen to make a grid of hexagonal keys and RGB LEDs, all controlled by a Raspberry Pi RP2040 chip.

Custom controller

“The HexBoard is primarily a MIDI instrument, which means that it sends note information to software or hardware sound generators that play the sounds based on the notes you play,” Jared tells us. “It has a USB-C connector for connecting to MIDI software on a computer and a TRS MIDI jack for connecting to hardware MIDI devices. It has a very basic built-in sound generator that can play over headphones or a built-in speaker, which is nice for when you want a quick and simple setup. All the unused pins from the RP2040 are exposed as headers on the board for ease of hackability for those interested in taking the hardware further.”

Jared launched the HexBoard in May 2023, and has since overhauled the design to make it easier to assemble and repair, and to add new features

On a piano, each key has two notes on either side of it; on the HexBoard, each key is touching six further keys, so you can physically reach more notes with one hand — which is useful if you don’t have massive mitts like Franz Liszt or Jimi Hendrix.

“The lit-up hexagonal keys allow for many different note layouts while indicating which note is which using colours,” says Jared. “The different layouts included make it easy to play chords using simple finger shapes that don’t change depending on the key, unlike an instrument like the piano. I designed the keycaps in TinkerCAD and designed the frame in Blender. I print everything on the Bambu Lab P1S, which just barely fits the frame into the build area.”

Why use RP2040?

“The RP2040 chip is the brains of the whole project,” he adds. “It reads the buttons, sets the lights, updates the screen, sends MIDI data, and generates simple sound waves. No proprietary software is needed to run this as it’s all handled by the RP2040.

“I appreciate how I can use PIO to handle updating the LEDs without blocking the CPU. I selected this chip for this project as it had all the I/O my project required with a good amount of headroom for future developments. That, plus it was very available during the big chip shortage that occurred in the early stages of this project.”

While big companies may relentlessly focus group products to make sure they find an audience, Jared originally made the HexBoard for a pretty small audience: himself. We reckon this might have enabled him to focus on making the HexBoard awesome.

Jared created his own custom RP2040-based board and added this to the PCB to handle all the ins, outs, and programming

“Originally, I made it for me and my brother,” he recalls. “I wanted a fun, hackable instrument that looked cool and was relatively easy to learn. I’m quite happy with where I am on that, so I’d say the maker/hacker/musician is my primary target.”

“As the project has advanced, it’s become useful to a variety of people. A beginner musician can use it to start learning basic chords and melodies. Any given melody or chord has the same shape/movement no matter what key you are in, so in many ways it has a simpler learning curve.”

“A music producer can use the various layouts to spark inspiration as each different layout gives a unique way to consider the relationships between notes. I know for me, I come up with different ideas on the HexBoard than I do on a standard musical keyboard.”

The screen enables users to navigate through the many layout options offered by the HexBoard

“With the latest update, it’s now a useful tool for those experimenting in microtonal music. The compact size and wide range make it very useful for musicians who want access to a large number of keys while still being able to easily carry it around in a backpack. Beyond this, the colourful lights and animations make it plain fun for anyone to play around with.”

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