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Human touch sensor

  1. Aug 11, 2009 #1
    hi there
    I'm up to design a device which switches on when human body touches it.
    I have a rough idea to use IR, Electrical phenomenas of body.
    But don't know how to start and where to start.
    help plzz
  2. jcsd
  3. Aug 12, 2009 #2


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    Staff: Mentor

    Welcome to the PF. Yes, you could use a near-focus PIR (passive infra-red) sensor, or a capacitive sensor, or a mechanical push-button. What can you tell us about each of those options? What are some other options?

    BTW, we do not do your projects for you. Tell us what your thoughts are on how to complete this project.
  4. Aug 12, 2009 #3


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    Science Advisor

    If you have two small capacitors in series, they will carry a high frequency pulse stream OK provided the load is high impedance.

    If you put a capacitor to ground at the junction of the two capacitors, this will reduce the signal getting through the series combination.
    Now, if this capacitor is a flat metalic plate on a thin piece of dielectric with a human touching the other side of it, you will get a similar effect.

    Is that enough to let you develop it yourself? Check out CMOS gates as an easy way to do this.
  5. Aug 12, 2009 #4


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    Gold Member

    It is not quite clear what you are asking.
    Making a sensor that switches on when a human touches it isn't very difficult.

    Making a sensors that switches on only if it is a human (as opposed to someone poking it with a stick) is significantly more difficult. Companies that develop and sell fingerprint readers have been working on this problem for a long time (because they want to make sure that the pattern their sensor is reading is on an actual finger -not a cast- and that the finger is still attached to its original owner), as far as I know there is no 100% perfect solution although although they are getting better all the time.
    As far as I understand they use a combination of methods: temperature, conductivity of the skin etc
  6. Aug 15, 2009 #5
    Thank you for the reply. I'm working on both capacitive sensor and pir sensor. For PIR senser
    what can be used as a lens? can a normal IR sensor be used?

    I also understand that conducting nature of moisture of human body can be used to achieve the goal.
    I'm trying make the switch operatable by feet too. but a wet shoe could also trigger the sensor in this... so 'human touch only' is failing in this!!
  7. Aug 24, 2009 #6
    This is dirt simple, if you don't care much for stability. Just cascade a few FET transistors if you touch the gate they should become conducting through the charges on your skin, I did it as a child once to turn a LED on and off, but I don't know what else will make it trigger.
    Last edited: Aug 24, 2009
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