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Very strange accidental proximity sensor - Explanation wanted

  1. Aug 5, 2013 #1
    Hello everybody,

    I was working on an electronics project, and one of the LEDs (actually I'm using only one) started acting really strange!

    It will light up when I come close to it, ONLY if I have been out of the room for some time!

    And that's not all, the period for which it will light up is proportional to how much I have been away (i.e. the longer I stay far from it the longer it will light when I return)

    I was thinking of 2 possible explanations how this can happen,

    Explanation 1. When I get out of the room I somehow get electrically charged, and this creates an E-field around the led when I return, making it conductive.
    (But it will do this even if I go the other way (i.e. what matters is that I stay out of range, not where I go))

    Explanation 2. The accidental sensor (be it capacitive or otherwise) is dependent on a capacitor that needs time to charge between "activations." But in this case it has a really wide range because I have to move 3~4 meters to get it to light again for a second or two!

    Any input on this is appreciated, thanks!
  2. jcsd
  3. Aug 5, 2013 #2
    I think there's a third explanation. Could it be that the LED is in love with you and the longer you are away the more it misses you?
  4. Aug 5, 2013 #3


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    No possible way to give you any advice on this unless we see a schematic.
  5. Aug 5, 2013 #4
    This gives me a grin. This is a classic when using CMOS components. When I was but a wee lad, my boss showed me a machine that he could actuate / de-actuate by waving his hand. It had an open gate and was picking up charge from his proximity (assumable he was charged).
  6. Aug 8, 2013 #5
    I had a similar event recently - something I could not explain but seems simpler than your situation.

    I was working with a microcontroller and had an isolated LED/resistor tied to ground. If I came close to the anode of the LED, it would very slightly eluminated. I made sure that I was not touching any charged electronics.

    More interestingly, if I firmly placed my feet on the ground then the LED would become dimmer. It seems that I was somehow conducting charge whilst sitting there.
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