Whereas different touch-sensing applied sciences exist, capacitive contact sensing is by far the preferred right now. Your smartphone makes use of a capacitive touchscreen, your laptop computer makes use of a capacitive contact pad, and plenty of units use capacitive buttons in favor of standard mechanical buttons. In the event you’ve ever appeared into including capacitive contact to one among your tasks, you then’ve in all probability seen {hardware} designed for that objective. However you could not want any particular {hardware} in any respect. In the event you’re utilizing a Raspberry Pi Pico improvement board, then you’ll be able to use James Brown’s easy code to show any pin right into a capacitive contact sensor.

Because the identify recommend, a capacitive contact sensor depends on capacitance. That refers to a system’s potential to retailer an electrical cost, like in a capacitor. However less complicated circuits exhibit a tiny quantity of capacitance and that adjustments primarily based on the proximity of conductive objects, similar to fingers. You might have seen that some touchscreens register a contact even earlier than your finger makes contact. That is as a result of their sensitivity is excessive and simply shifting your finger close by triggers a detectable change in capacitance. Brown’s code makes use of the Raspberry Pi Pico’s built-in {hardware} to carry out the identical operate and it really works with any GPIO pin.

The code first units a pin to an output and pulls it low. Then it instantly switches the identical pin to an enter with the inner pull-up resistor lively. There’s a tiny time delta between the 2 occasions and that adjustments primarily based on a finger affecting the capacitance. The Pico’s PIO (Programmable Enter/Output) measures the delta and the entire course of repeats about 60 instances a second. The code returns a price between 0 and 1 primarily based on the delta, with 0 being no detectable distinction from the norm and 1 being a really robust distinction. Customers can select a threshold to set off an motion, which ought to correspond to somebody touching a bit of conductive materials related to that exact GPIO pin.

Brown’s code is just meant to work for capacitive buttons and will not be appropriate for 2D capacitive contact pads or touchscreens. Nevertheless it ought to be very helpful for anybody utilizing a Raspberry Pi Pico that want to add capacitive buttons to their subsequent venture.