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TTP223 touch sensors self-triggering bug

Discussion in 'Sensors and Actuators' started by Head Crusher, Oct 25, 2016.

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  1. Head Crusher

    Head Crusher

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    Feb 12, 2013
    I have three TTP223 touch sensors connected to a power source (only VCC and GND are connected).
    I intentionally didn't connect I/O pin to Arduino because I suspected that it could cause the problem (trigger the sensor by accidentally sending current to the I/O pin). One of the sensors gets triggered and starts blinking, please see the video:
    https://www.dropbox.com/s/y0eeg959fybolfz/IMG_0495.MOV?dl=0

    I fail to reproduce this bug consistently and don't know what causes it. I've noticed the following:
    1. It happens only on the 1st and/or the 2nd sensor only if they are both connected (but after switching sensors and then assembling this same setup - sometimes this bug disappeared).
    2. Thought they were too close together and were triggering each other but I tried putting other sensors even closer and it didn't happen.

    I would be very grateful for any ideas on why this is happening, thanks in advance!
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,361
    2,757
    Jan 21, 2010
    I'm not going to sign up to dropbox to view your video. Upload it to youtube or similar.
     
  3. Harald Kapp

    Harald Kapp Moderator Moderator

    9,900
    2,097
    Nov 17, 2011
    Neither will I.
    In this case, however, you don't have to sign up, Steve, although the popup irritatingly declares so.
    I just clicked the popup away and was able to see the video.

    @Head Crusher : The sensor may be triggered by the capacitance between sensor and the breadboard. Try increasing the distance between the two (and possibly the distance between the sensors, too).
     
  4. Head Crusher

    Head Crusher

    4
    0
    Feb 12, 2013
    Thank you!
    I think the proximity of the sensors may be the issue here. Been testing this a little bit more and if I put the sensor about 1-2 cm farther the triggering doesn't start.
    However if I put them close to each other (about 2 mm) it MAY (or may not) start triggering itself. And if it happens - always on the same sensors. Could this be the problem?
    How is it possible to fix it without changing the distance? Maybe I can isolate the sensors from each other somehow?
    (I tried sending logic LOW to the sensor's output pin and this made it unresponsive, meaning real touch wouldn't trigger it, but the sensor nearby was still getting triggered. It would stop if I completely turn off the first sensor)
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    9,900
    2,097
    Nov 17, 2011
    It seems you can adjust the sensitivity of the sensor by changing a capacitor on the sensor PCB.
    You can also try to decouple the sensors (reduce their mutual influence) by putting a piece of electrically conductive material at 90 ° angle between the sensors and connectingb this material to ground potential (0 V). A piece of sheet metal of a piece of copper clad PCB can be used. This setup, however, will be a bit challenging to realize in a device.
     
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