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FDC2112-Q1: FDC2112 poor signal

albert galofre
Prodigy 30 points
Part Number: FDC2112-Q1
Other Parts Discussed in Thread: FDC2112

Hi there,

I'm developing a capacitive sensor with your device FDC2112.

The problem is that I get a really poor signal between touch and not touch. Just only 15 counts!!!!

Probably I'm doing something wrong.

Attach a pdf with the design details.

Could you suggest some improvements? 

thanks a lot.

Poor signal FDC2112.pdf

  • 0
    TI__Genius 17440 points

    Hi Albert,

    I have 3 suggestions for you to try:

    1. Your sensor oscillation amplitude is actually a little low. You should measure the amplitude after it has settled to a stable value, not at the maximum voltage. Vamp should be between 1.2-1.8V after the measurement has stabilized.
    2. Your register configurations don't show changes to the OFFSETx and RESET_DEV registers. You may be able to maximize the dynamic range of your signal by taking advantage of the gain and offset features of the device. These features are discussed in section 9.3.2.1 of the datasheet.
    3. The sensing range and resolution is dependent on the electrode size. You may need to increase the size of your electrode or decrease the thickness of any layers between the electrode and the user's hand.

    Best Regards,

  • 0 in reply to Kristin Jones93
    Prodigy 30 points

    Hi Kristin,

    Thanks a lot for your support, is really valuable, as always with the TI tickets.

    I have improve the signal sensitivity BUY just a bit. I have increase the gain, and reduce the "DC level" with the offset. The SNR has improve but just a bit.

    Thinking about how to manege the signal I have realize on hard aspect.

    I'm trying to make a water level sensor in a metal tank connected to earth. So no superficial capacitive sticker are useful. Then I thought to use two probe sensor, just a metallic sticks on the water isolated from the metallic tank of course.

    Have a look to the "set up tank.png" : you can see the first probe to show the LOW; and the second to show the FULL. (The medium probe is not connected.)

    On the other side have a look to the "set up tank SIGNALS.png": you can see the first probe signal (red) and the second (black) signals

    As you can appreciate:

    - Empty the signals are quite equal

    - Touching the first probe, its signals start to increase. That's good.

    - Touching the second probe, both signals goes to 0 quickly.

    So in this scenario seems that the WATER give an "acceptable" signal to ONE PROBE. BUT when both touched the water, then seems "short circuited"

    I have configured the device in "Auto-Scan Mode Enable" (NOT secuencial), with a delay between the samples, just trying to separate both channels. But unsuccessful. The same results.

    That's means that the FDC is not an adequate when the channels are joined with water.

    What do you think? You agree with me? 

    thanks a lot

  • 0 in reply to albert galofre
    TI__Genius 17440 points

    Hi Albert,

    My apologies for the delayed reply. I agree, the FDC's electrodes should not be directly in contact with the water. If you cannot use a sensor on the exterior of the container, you might consider an approach like the immersive straw technique.

    Best Regards,

  • 0 in reply to Kristin Jones93
    Prodigy 30 points

    Hi Kristin,

    Thanks a lot. Unfotunadently this is expensive solution.

    I have to think in other ones.

    In any case, thanks a lot for your interest.