In CircuitPython, for chips that don't have built-in capacitive touch detection, we connect a 1M external pulldown (and of course disable the internal pulldown). To do touch detection, we bring the pin to 3.3V, and then switch it to an input, and measure how long it takes to discharge. This didn't work on the RP2350 because of the latching, and was how we discovered that the internal pulldown did not need to enabled for the latching to happen. This is why my reproducer in https://github.com/raspberrypi/pico-feedback/issues/401 uses a 1M resistor -- it was what I had at hand while trying to debug the problem.
We could maybe just reverse things and do touch detection with a pull-up, but that puts the touch pads at a quiescent 3.3V instead of grounded, which is not so desirable.
We could maybe just reverse things and do touch detection with a pull-up, but that puts the touch pads at a quiescent 3.3V instead of grounded, which is not so desirable.
Statistics: Posted by dhalbert — Sat Aug 31, 2024 5:36 pm
