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What is my sensor sensing?

  1. May 25, 2016 #1
    I have a controller with 3 pins for a sensor input. Positive, Negative, and Signal. I placed a wire on just the Signal.
    The controller reads out the varying voltage across the signal wire/pin.
    To the wire I attached a piece of Aluminum.

    Every time I touched the aluminum with my finger the voltage would go from 0v to some other value such as 0.3-0.6v
    Same thing when I touched it with a metal object.

    Nothing happen however when I touched it with paper or plastic.
    Is this an induction sensor? I just need to be sure.

    Thanks in advance.

    Attached Files:

  2. jcsd
  3. May 25, 2016 #2


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    hi there

    since you haven't actually connected a sensor to the input
    your controller is just recording random tiny fluctuations of voltage
    you can do the same with a multimeter in low voltage or current ranges

  4. May 25, 2016 #3


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    I suggest it is a capacitive sensor, which senses ac-conducting materials.

    You are right: It cannot sense paper ( and wood ), but it can sense glass ( and various types of plastic ). It can be made extremely sensitive.
  5. May 25, 2016 #4


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    Note: he wasn't actually using a sensor he was just connecting a random bit of wire to the signal in pin where the sensor would plug in

    @kolleamm .... it mite help if you gave us more info ... eg what is the controller ... photo, www link etc, what sensor would normally plug into it ?

  6. May 25, 2016 #5
    Thanks for the help guys!
    The controller is called a Maestro Servo Controller. It is designed to pulse width modulate servos and detect input voltage around 0-5v from analog voltage sensors.

    Whatever sensor it is you can use it as long as it gives you a voltage used for measuring input.
    Would this likely be measuring capacitance?
  7. May 25, 2016 #6
  8. May 25, 2016 #7
    The fluctuations in the voltage were fairly distinct when the objects were touching and not touching.

    While touching it was around 0.3v-0.6v.
    While not touching it was around 0.0v - 0.1v.

    Regardless of how long it was touching or not.
  9. May 25, 2016 #8
    I word of caution:
    This sensor input signal may be ESD sensitive. You may damage it by touching it with fingers, plastic etc.
  10. May 25, 2016 #9
    Good point, ultimately I'm just going to make 2 metallic plates that touch each other, the top being covered to prevent ESD. It's supposed to be a touch sensor for a robotic arm to prevent bumping into objects.
  11. May 25, 2016 #10
    Just out of curiosity what could I add to the wire to prevent a high current from passing through it such as a high ESD? Connecting it to ground would probably make the sensor useless.
  12. May 25, 2016 #11


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    As davenn said,
    Your body is capacitively coupled to the environment.

    https://www.audereaudio.com/images/human-noise-injection.png [Broken]
    Image compliments of https://www.audereaudio.com/faq_punoise.htm [Broken]
    Last edited by a moderator: May 7, 2017
  13. May 25, 2016 #12
    Looks like the analog inputs are same structure as digital inputs and include ESD protection diodes, so you may be ok unless you are in an ESD harsh environment.

    Attached Files:

  14. May 26, 2016 #13
    Interesting, would there be any scenario where the wire would not read any noise from other materials perhaps if there are no high current power supplies nearby? I'm trying to determine if this would be a reliable proximity sensor.
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