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conductive rubber switch question

Discussion in 'Electronic Basics' started by tempus fugit, Jan 19, 2009.

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  1. tempus fugit

    tempus fugit Guest

    Hey all;

    I'm designing a switching system using a uC and am thinking about using some
    of those little conductive rubber switches to short an input to ground to
    the uC. I had planned to use the pullups on the uC, or use 10k resistors as
    pullups. Will the conductive rubber be able to handle the small (I guess
    5/10 000 = 0.5 mA) of current or do I need to use something more robust?

    Thanks
     
  2. Jasen Betts

    Jasen Betts Guest

    10K is probably too small, try 100K (or the internal pull-ups)

    if you're (still) worried about heating of the rubber turn the pullups off
    while not needed.
     
  3. neon

    neon

    1,325
    0
    Oct 21, 2006
    Those little rubber switches are not rubber but ruther carbon switches. Rubber is a very good non-conductive.
     
  4. Eeyore

    Eeyore Guest

    It should be on the data sheet.

    As Jasen says, I'd tend to err on the higher side for pullups (or indeed use
    internal ones).

    Graham
     
  5. Nemo

    Nemo Guest

    I would think the conductive rubber will be able to take 0.5mA no
    problem, though the datasheet will say for sure. Consider the surface
    area dissipating the power, and compare with a resistor. In general, a
    relatively high current like that will make the input more reliable. My
    reasoning is thus. If the pullup is as high as 100k, it is easy for RFI
    / ESD to generate a false signal. The extra current drain (0.5mA versus
    0.05mA) is only momentary so is not relevant to battery life, if you're
    using batteries.
     
  6. tempus fugit

    tempus fugit Guest

    Thanks Nemo.

    I would think so too, especially in this application (the rubber is being
    used to short to terminals like a momentary switch and will only have the
    current passing through it for a second or less). I can't consult any data
    sheet because the rubber is just something I've salvaged off of other
    devices.

    Thanks
     
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