The old ones are wearing out. I used conductive foam for my home-made force sensitive resistors, and it eventually stops being foam, and starts being a block of carbon laced goo. This doesn't work well.

So building some new ones.

Was walking through Microcenter and spotted an inexpensive anti-static work surface. Looks pretty tough and is large enough to make two set of pedals for $15.

It's basically a layer of carbon laced rubber and a layer of plain rubber bonded together.

I grabbed a Teensy 3.2 (as it does USB MIDI out of the box), and headed home.

Soldered a few bare copper wires to some perf board and tested the resistance. Two wires, 0.1in apart, 2 in long at 30lbs of force gave ~140k of resistance. That's a bit high for an ADC input to a microcontroller.

Added more wires and it drops some. So the contact area is related to the resistance, although the force per unit area also drops so it's not linear.

Tied both wires together, and measured the resistance to the grounding strap connection. Virtually the same reading.

Moved the contact point around the pad. The resistance varies, but only by 10% across the pad. I can calibrate for that! One connection to each button, and a couple tied grounds and I'm in business.

A project is born.