I just realized. Apparently I never uploaded the hardware source files for this. Wow, how time flies.
I do remember 7 failed branches of ideas working towards a print-flat, pop through, TPU button, and finally one 'good one'.
I'll get at least the good one uploaded when I sort out what is what.
This version added a cutout for a Dotstar module to shine through from the bottom. This eliminated wiring within the button itself. Also, placing the module inside the button made for a rather unattractive point light source, whereas putting it below gives it a larger distance to spread out.
There may have been polyester fiber-fill involved as a diffuser, but I can't remember which worked better. Experiment!!
In any case, the dome shape and disc get covered in AL foil with spray glue, and a sheet of non-aluminized mylar (gift wrapping plastic) placed between them for use as a dielectric.
This formed the capacitor that the Teensy could read. Pressure applied to it would deform the dome and increase the capacitance. It was still more of a log() curve than linear response and perhaps some scaling is in order.