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Author Topic: CTMU Capacitive Touch Sensing - Doubt  (Read 3216 times)

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CTMU Capacitive Touch Sensing - Doubt
« on: July 28, 2013, 05:49:29 AM »
Dear Sir/Madam,
    I am Jayaraj.A from Bangalore. I am using 18LF45K80 for capacitive touch sensing (CTMU). I am charging the touch pad (capacitor) periodically at 5.5uA.
   When I touch the touch pad directly with finger (without any overlay), my ADC sensing voltage reduces, as the total capacitance increases. This logic works correctly.
Problem with overlay:
   I had used a non-conductive overlay- Acrylic sheet of 2mm thickness – covered on the top of the touch pad. At this moment, if I touch the overlay, the voltage increases, which means the total capacitance got decreased.
  So the doubt is: with an overlay on the touch pad, does the total capacitance decreases??
Kindly reply us.
With regards,


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Re: CTMU Capacitive Touch Sensing - Doubt
« Reply #1 on: July 28, 2013, 10:33:34 AM »
Adding an overlay will certainly change the capacitance. What you want to do is to measure the capacitance every time you start the PIC. This way you will know the reference capacitance.After that, you are sure that when you touch the button the capacitance will increase regardless of what overlay you have.