I’ve been using this product for development of my interface. Here some things I’ve learnt about it
The contact of this product works using conductive silicone. The conductive silicone has the property of changing the resistance when it is under pressure. I measured the range to be between 2 and 0.008 K.ohm. This was tested using the same pcb etch that is used in the original sparkfun board, but in a custom built board that is using tin plated contacts.
The 2 K.ohm resistance happens when just one side is slightly touching the contacts. The 0.008 K.ohms happens when the button is being pressed firmly, but within a normal range. Anyways I think that the relation between resistance and pressure slope will get weaker and weaker. According to my understading, lower resistance values will result in a larger voltage variation.
I have used this effect. In that use case, I was measuring each button behind a multiplexor, and I applied a pull-down resistor of 470 ohms in the common pin. I believe that any pull-down resistor between 1.8 and 400 ohms will result in a pressure sensitive matrix, assuming that the matrix output is collected by an analog pin, of course. I don’t recommend using this setup if you expect to use a digital pin, because slight pressures could result in button detection, leading to bounces and a poor overall interaction.
Using a text editor it is possible to import sparkfun’s routes. This process will be explained at changing the layer of routes on kicad.