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Using Touch Sensing Controller on STM32L053R8 nucleo64

Question asked by galand.lucas on Apr 18, 2016
Latest reply on Aug 29, 2017 by Jaroslav Becka
Hi everyone,

I'm trying to set up 3 capacitive touch keys using HAL touch sensing controller library but I'm facing some problems. I followed the instructions in AN2869 application note for implementing one sensor using Active Shield. The TSC is initialized with CubeMX. I have a 10mm x10mm copper touch key connected to pin PA6 (G2_IO3) and the corresponding sampling capacitor (10nF) on PA7 (G2_IO4). The active shield is connected to PA11 (G4_IO3) and correponding sampling capacitor is on PA12 (G4_IO4). I placed a 2.5mm plastic overlay on the touch key.

The problem is that I have too much parasistic capacitance and a touch is always detected. I tried to disconnect the touch key from the mcu but even without the touch key I see the voltage on the sampling capacitor increasing with the counts.

What am I doing wrong ? Is the touch sensing controller on STM32L053 nucleo board recommended to detect touch events through 2.5mm plastic overlay ?

Thank you,