STM32Cube_FW_L4_V1.13.0 Touch Sensing Library multiple buttons in same group not working on STM32L476

[WDe K.15]

I tried to implement 7 touch buttons on a STM32L476, 3 on IO2,3 of group 1, 3 on IO 2,3 and 4 on group 2 and 1 on io2 of group 3. Samping caps are always on IO1 of the respective group.

As I wanted to process the buttons all at the same time, I created 1 bank. I then have the effect that all buttons on the same group seem to react on any touch of the 3. So i could only detect 3 out of 7 buttons really, 1 on each group.

I then created 7 banks, each with 1 button. And then it does work well.

So my first question is, as there was no example project with more than 1 button, has the software really been validated on the STM32L4? Because I think this is a bug.

I could combine 6 of the buttons in a rotary or linear touch sensor, but there was no such example for the STM32L4 in the STMCube firmware. Is this still to come? Should I look at other microcontroller families and copy from there?

[OlivierR]

Regarding acquisition and group:

• In your case (see picture bellow)
  • To get 7 sensors at the same time you need
    • 1 bank
    • 7 groups, mean 7 sampling capacitor
  • To get 7 sensors in 2 times you need
    • 2 banks
    • 4 groups, mean 4 sampling capacitor
  • To get 7 sensors in 3 times you need
    • 3 banks
    • 3 groups, mean 3 sampling capacitor

Regarding wheel or rotary

• To get 6 channel information, you need to latch 6 channels at the same time
  • To get 6 sensors in 1 time you need
    • 1 bank
    • 6 group, mean 6 sampling capacitor

I will recommend to add an extra group dedicated to shield.

This picture shows TSC, group, bank, acquisition dependencies:

You can get deeper information on AN5105.

Rgds