The code lives here: https://github.com/paigeplan/music158_cap_keyboard. I had originally made the instrument to work with only with a Max patch that I had made a while back, but now it is a general MIDI controller with polyphonic aftertouch, pitch bend, CC, and sensitivity control. Right now, I've been using chorded button combinations to select between different presets and scales. My main reason for making it was to have something I could easily program for any application.
Here's a song I made with it:
Here's a video of it in action
And here is a video of the copper part being milled out. I used an Othermill, and made the file with Eagle.