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Capacitive touch sensor project

Discussion in 'Sensors and Actuators' started by carebare47, Jan 17, 2011.

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  1. carebare47

    carebare47

    66
    1
    Oct 21, 2010
    Hello,

    I am doing A-level electronics and have just started my coursework project. I wanted to try and design/build the kind of touch sensor that you can find on some lamps, where you come into contact with metal on the lamp and this turns the light on. I think that these work by sensing capacitence. I have looked online but can't seem to find much on this. Is there a simple-ish way of doing this, or is it not worth trying?

    Many thanks,

    Tom
     
  2. shrtrnd

    shrtrnd

    3,688
    457
    Jan 15, 2010
    You can do it, but it's not a simple circuit, it'll take some parts.
    For safety reasons (isolating yourself from the power outlet), you have to be pretty careful.
    I figure there's a circuit available somewhere on Google, but I cheated when I did my
    first one. I bought one from All Electronics Corp in California for $2. Then disassembled it,
    and made a circuit I thought was more reliable (the one I bought was bare-minimum in
    current and wattage capacity). Maybe somebody here will direct you to an available
    circuit online.
     
  3. carebare47

    carebare47

    66
    1
    Oct 21, 2010
    Managed to find a schematic that uses 12 NOT gates to generate a pseudo sine wave that excites an 'antenna'. When you touch the antenna it disrupts the signal slightly, the circuit detects this and is switching a LED through a MOSFET. It works, but it was too easy =P Think I am going to add PWM on with a 555 and use that to have different sound levels or something =) Thanks for the help, and any further advice/ideas will be welcome ^_^
     
  4. shrtrnd

    shrtrnd

    3,688
    457
    Jan 15, 2010
    Hmmm, I never thought of an LED as a 'lamp' before.
    Learned something new today.
     
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