How do Dualshock 4 pressure sensitive buttons work?

Question

I'm doing a reverse engineering research about the PlayStation 4 controller. I want to know how do the analog buttons work (the triggers in the bottom, not the analog sticks). I've found a nice teardown album and, there, I've seen this image:

I know from this page that the flexible film pins for each analog trigger are these:

• Common: Oscillating between 0 and 3.3V.
• Sig: Voltage divider output, active low.

I want to know if it is:

• A capacitive sensor.
• A piezoelectric film.
• A force-sensitive resistor
• Other

And, by the way, how does the circuit attached work? I suppose it will have some kind of Analog Digital Converter, filtering, amplification...

Answer 1

It has the apearance of a force sensitive resistor, the (lower) conductive dome behind the button squashes, progressivley bridging more and more of the resistive stripe (black rectangle) as the force is increased. Thus the harder you press the lower the resistance.

There will be some sort of analogue to digital, but I can't see what sort they are using. but given that the description says "voltage divider output" that suggest that the resistive button is used in a voltage divider and that the output is sensed with a voltage sensing ADC, probably built into the microcontroller tha runs the gamepad.