STM32 Touch Sensors

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Only some STM32 processors have touch sensor circuitry built in, most noticeable the STM32Lxx series.

STM32 Processors with Touch Sensors.png

Hardware Example

As part of another project I was using an STM32L432 MCU and while doing that design I decided to add 3 touch sensors.

Schematic with touch sensors.png

The circuitry involved in the touch sensing is the C5 and the actual touch pads J2, J3 and J4 and their accompanying resistors.

Layout wise I did two different approaches:

Touch PCB Layout.png

The top and bottom touch pads are just big single sided SMD pads which is covered by soldermask. The center "hole" is a big through hole pad.

The gadget came out like this:

Touch PCB.jpg

Software

Messing around with this it turns out that the middle pad (the through hole one) is much to close to the neighbors, so in the software example I only deal with the two pads covered by soldermask.

TSC Pins.png

Resources

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