The Colmi R02 is one of the cheapest smart rings on the market. It costs about $20, and is remarkably easy to hack. [Floyd Steinberg] took advantage of this to turn it into a rather unique MIDI controller.

What makes the Colmi R02 somewhat unique is that the manufacturer did not try to lock out users from uploading their own firmware. You don’t even really need to “hack” it, since there is no code signing or encryption. You can just whip up your own firmware to make it do whatever you want.

To that end, [Floyd] set up the ring to act as a device for musical expression. When connected to a computer over Bluetooth, data from the ring’s accelerometer is converted into MIDI CC commands via a simple web app. The app allows the MIDI messages to be configured so they can control whatever parameter is desired. [Floyd] demonstrates the ring by using it to control filter cutoff frequencies on an outboard synthesizer, with great effect.

You could theoretically just strap an accelerometer to your hand with a microcontroller and achieve similar operation. However, the magic of this is that it costs only $20 and it’s already in a form factor that’s optimized for wearing on your finger. It’s hard to beat that.

Files are on GitHub for those eager to experiment. We’ve previously featured some hacks of this particular smart ring, too, with [Aaron Christophel’s] efforts directly inspiring this work.