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Touch sensing design for MCU

Question asked by Husam Danial on Nov 27, 2017

Dear supporter,

I am using STM32L05 in my project. the Microcontroler shall detect  proximity/touch sensing. 
my question related to the electrode design which shall be connected to the MCU (TSC_IOGxCR) .
I shall design 2 electrodes - flex board as described in attached file (Double Sensor flat T cable) page 2,  as you can see on component side shall be a mesh copper connected to the ground board, on the print side shall be copper poured and between these layers shall be isolated material. 
then the flex board (contain 2 electrode with its wires) plugged in connector(Molex). then from this connector we get the ground net and get the sensing from the electrode to the MCU (TSC_IOGxCR).
The questions are:
1. what isolated materials should I use in order to make the electrode works properly for sensing?  (range of the relative permittivity, between the layers and betwen electrode and my finger)
2. as mention in AN4312 Application note, the mesh ground plane should be 10%, does it work properly with our electrode? is there any range should I take into account?
3. is there any constrains for the wire's length/width/Impedance/capacitance.. from the electrode to the MCU?
4. is it okay to connect the electrode through a connector to the MCU? (does the Molex connector add capacitance that shall defect the sensing?)
in other world, does my design will work properly with few changes that I should do, in case yes what are the changes?

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