I've been posting about this in various topics but now that it's on Github, I thought maybe it's time to give it a topic of its own. From the README:

My goal is to eventually replicate the keyboard and sound of the bass side of an accordion in an electronic device that accordion players will find easy to adapt to. So far I've built three prototypes:

• Prototype 1 was trying out a Teensy 4 with an audio shield on a breadboard, with 4 bass buttons.
• For prototype 2, I put the buttons on two double-decker circuit boards (9 bass buttons). Here's the Video. You can see the remains of prototype 1 in the background.
• For prototype 3, I built a real case out of wood and laser-cut acrylic panels, to make a desktop device that's more easily portable. This one uses a Teensy 3.6. Here's the Video. I designed it in Onshape and you can look at the CAD model online.