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touchplate dimmer switch oddity

Discussion in 'Electronic Basics' started by andy, Aug 20, 2004.

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  1. andy

    andy Guest

    In my front room, I have one of those dimmer switches where you touch a
    metal plate on the front to turn the light up or down. Sometimes it stops
    working, which I've always put down to dry skin or something, assuming
    that it works by sensing your body's capacitance.

    I found out the other night that when it's not working, it does still work
    if I go 3 or 4 steps up the staircase that the dimmer switch is beside,
    and touch it from there. The only explanation for this I can think of is
    that I know there's a natural vertical electric field going up from the
    surface of the earth, so maybe it has something to do with that. Or else
    it has something to do with my body picking up on the magnetic field of
    the electric wiring in the house.

    Does anyone have any ideas about this? I'm not just asking out of
    curiosity - I've had a bad feeling about this house, and that room in
    particular, for some time, and this has started me off thinking that this
    may be partly caused by electromagnetic interference from badly installed
    wiring. I had a go at checking this out by holding the probe of an
    oscilloscope and moving round the room, and the 50 Hz signal from my body
    does seem to get stronger when I move near that wall. Stronger still when
    I touch it, which is slightly worrying. Maybe damp in the wallpaper
    is acting as an aerial. There's also a slight spike in the signal on every
    half wave, which I guess is from the thyristor in the dimmer. I remember
    reading somewhere that low frequency EM fields can have effects on mood /
    mental health, so I'm wondering if that could be the reason. I haven't put
    on my tin foil hat just yet - just trying to work out if that's
    contributing to my weird mood swings.
  2. Bob Masta

    Bob Masta Guest


    As a scientific wild-ass guess, I'd suggest that when you
    are reaching from up the staircase, you are moving your
    body closer to a conductor in the wall, making a better
    capacitive coupling for the touch sensor.

    I wouldn't worry too much about evil low-level E-fields. I have
    yet to see any compelling data on this. The reports I've seen
    were either on decidedly non-standard situations (like
    60 Hz modulated microwaves focused on cell in a lab dish)
    or they had serious methodological flaws and results barely above

    You could do your own blinded study. Presumably, the fields you
    are concerned about are from your own house wiring, and would
    be stopped by pulling the master breakers. The trick is making a
    blinded study of this; you *have* to make it so there is no way for
    you to know which position the breaker is in. So you'd have to
    start by unplugging all the clocks and VCRs that have displays,
    as well as the fridge, A/C, and stuff that has running motors.
    An assistant near the breaker box would then throw the switch to one
    position or the other. You'd probably have to leave the house
    while this was done, since you could otherwise tell from the
    sound of the clunk. Use a schedule of so many minutes in each
    position, using random positions from some standard table that
    the assistant has but you don't see. Record your feelings in
    each interval and compare later to the actual breaker conditions.
    Make sure you have many random repeats, say a dozen or so.

    Of course, if you find no effect, you can't rule out that there
    would have been one if all the applicances had been running
    normally, changing the evil field patterns.

    Best regards,

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
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