This PCB Puts a Polyphonic Piano in the Palm of Your Hand

After experimenting with touch-sensitive capacitive PCBs, sjm4306 decided to use this technique to create a single-octave keyboard. The pocket-sized device is meant as a gift for his sister, who is a practiced pianist. From the looks of his demo just after 12:30 in the video below, it seems sjm has at least touched a piano before as well. Based on the keyboard’s excellent construction, however, we’ll assume his skills like primarily in the engineering realm.

The keyboard is constructed with a matte black solder mask, along with white and black areas to indicate the 13 keys that can be played. An ATmega328P is implemented for control, and a small surface-mount speaker takes care of actually playing tunes. What makes this build especially impressive is the fact that it can play four notes at once – making it polyphonic – though anything pressed after the first four keys will be ignored. These notes are fed to the speaker via four different outputs to give a summation of the sounds.

The PCB piano sounds surprisingly good, and while objectively small, it's big enough to be used by actual human-sized fingers. As of now, it's powered by one CR2032 battery, though it appears to perform better when using a power bank, and the next iteration will likely feature a second coin cell for enhanced performance.

Although it's still a bit of a work-in-progress, design files are available in the project's write-up.