[insane_dreamer]

It seems the keyboard is pressure sensitive (reference to a pressure sensor in the HW section)

[seniorsassycat]

Pressure sensor is in the mouth piece.

I've always thought saxophone keys were on or off

[javier_cardona]

Actually the pressure sensor is on the PCB. Pressure is transferred from the mouthpiece through a flexible silicon pipe. You can see the details in the assembly instructions here: https://github.com/jcard0na/haxo-hw/blob/main/docs/assembly....