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Graphite touch button

  1. Dec 10, 2016 #1
    graphite has high conductivity , so i though of making a touch button out of a pencil drawn pattern on the wall.the pattern is shown below.
    when not touched -resistance between ends of the pattern >200Mohm (exceeds dmm limit)
    when fully pressed - resistance between ends of the pattern = 1.3 Mohm.
    but Vout rises after delay or falls after delay of some 100 ms.due to high impedance
    this pattern connects skin resistances in parallel
    can someone suggest a better pattern ( of lower end to end resistance) ?
    for faster response
    Last edited: Dec 10, 2016
  2. jcsd
  3. Dec 10, 2016 #2


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    Staff: Mentor

    Hi hackhard. You probably have the transistor drawn incorrectly on your schematic.

    I like your experimental bent, but a problem with a graphite pattern is that it will sooner or later probably smudge and establish a bridge between the tracks.

    In future please keep images to under about 1000 pixels across, otherwise the thread gets displayed in tiny sized print to accommodate the oversized image on our screen.
  4. Dec 10, 2016 #3


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    Search : ' electroconductive ink pens '
  5. Dec 10, 2016 #4
    its very costly
    mine is a cheaper solution
  6. Dec 10, 2016 #5


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    2017 Award

    but not reliable ... cheapness come with disadvantages as @NascentOxygen said
  7. Dec 10, 2016 #6


    Staff: Mentor

    Here is a very different approach to do what you are doing. Perhaps you could have fun with a project to do that.

    Graphene has been made with pencil lines and scotch tape. https://en.wikipedia.org/wiki/Graphene#History
  8. Dec 10, 2016 #7
    thanks for help. ive decided to use conductive ink
  9. Dec 11, 2016 #8
    conducting paint is too expensive.
    are there any other alternatives to copper foil strips or Bare conducting paint
  10. Dec 11, 2016 #9
  11. Jan 4, 2017 #10
    If you want resolution try making a lense to spread out a cheap dollar store solid state laser onto a inner reflective box frame and lining the inside parameter with a grid of cut mirror reflector's each precisely cut at width and angle's prime to each other and spaced at exact intervals, with incident angles toward two or more LDR(light dependent resistors) and coordinates of blocked pulse's like finger tips can be extracted easily though any serial adc.
  12. Jan 4, 2017 #11

    jim hardy

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    Try increasing R2 to 220K and pulldown to 10 meg ?
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