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Thread: Touch Sense through soldermask? And any advice for pad-shape?

  1. #1

    Touch Sense through soldermask? And any advice for pad-shape?

    Hey everyone,
    So I'm wanting to do a simple capacitive touch sense switch (just off or on) using the Teensy. I'm currently designing the PCB pads and wondering I can leave the soldermask on? This would definitely be a preference for me, so I don't show any bare-copper and can choose the soldermask color.

    Attached is a screenshot of my PCB touch pad I'm working on, it is ~ .75" x .5".

    Click image for larger version. 

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    One of the traces is going to go to the teensy and the other is ground. In my first tests (just using copper tape), I get a much stronger output from the capacitance sense pin if my finger is also touching ground. Maybe this is because my application is not tied to mains earth.

    Interestingly, on my tests I get a much better signal to noise ratio using the generic arduino CapacitiveSensor library compared to the Teensy specific one.

  2. #2
    Senior Member pictographer's Avatar
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    Should be fine to cover the traces with solder mask.

    The touch sense hardware has tuning parameters. You might want to take a look at the source code for touchRead.

    You might want to include code to automatically calibrated the sensor. The baseline reading varies with humidity or temperature.

  3. #3
    Quote Originally Posted by pictographer View Post
    Should be fine to cover the traces with solder mask.

    The touch sense hardware has tuning parameters. You might want to take a look at the source code for touchRead.

    You might want to include code to automatically calibrated the sensor. The baseline reading varies with humidity or temperature.
    Oh interesting, I thought touchRead and capacitiveSensor already did some sort of self calibration.

  4. #4

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