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started 2021-03-117 commitslast push 2022-04-05

Test Touch Pad PCB

A PCB touch pad based on the TTP223

electronics pcb prototype

Touch Pad PCB Test

For an upcoming project I wanted to test how to implement PCB touch pads. The easiest solution that I could find was to use the TTP223 IC. All in all the design was pretty easy and straightforward.

There were mainly three things to experiment:

  • does my custom touchpad footprint work?
  • is the minimal spacing between the pads enough?
  • what size should the capacitor be?

The first two questions could be answered easily, the last one took some further investigation. The datasheet says that the capacitor should be in the range between 0 and 50pF. Some testing reaveled that 22pF seems to be the optimum for my 1.6mm thick PCB. 0pF is way too low. It triggers a change even if my finger is still a few centimeters away from the pad. This could work as a general proximity sensor, but not as a touchpad. 50pF on the other hand was too much. You have to press quite strong with your finger in the center of the pad in order to register any contact at all.

step 1
(testing the touchpads - it works!)