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please HELP very important... water leakage sensor

Discussion in 'Electronic Design' started by Big House, Feb 19, 2006.

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  1. Big House

    Big House Guest


    I have bought a home alarm system that has window/door sensors. This
    sensor has a circuit that alarms the system when the internal reed
    switch goes from closed to open. Which means someone opened a door (the
    sensor goes next to a magnet, when the magnet goes far, the reed switch

    If it goes from open to closed nothing happens.

    I have an urgent need that is transforming the window/door sensor in a
    water leakage sensor. Before finding how the window/door worked, I
    thought of connecting two wires to the contacts of the reed bulb: when
    the water would close the circuit, the sensor would alarm, since I
    thought it would check of change of status.

    But, like I said, the sensor works only if goes to close to open.

    When I tested my "water leakage sensor", infact, I put these wires in
    the water and nothing happened. But as soon as I take them out, it
    alarmed the sensor!

    What I need is the simpliest way to "invert" the status of the sensor
    so when the water closes the circuit, it alarms.
    Or something that, when the circuit is closed by the water, it sends a
    close then open to the sensor. Or goes closed>open>closed

    In a few words, if the water closes the circuit, it should open the
    circuit instead of closing it.

    What the SIMPLIEST way to do it?

    Thank you very much!!!
  2. Ross Herbert

    Ross Herbert Guest

    Make and model of your alarm system would be handy to know...
    Some alarm systems have auxiliiary trigger inputs which will accept a
    normally open input trigger as well as the normally closed window
    sensor inputs. Check yours out to see if it does have this facility.
  3. I saw a goofy little sensor once that consisted of a leaf-type
    microswitch and a flattened sponge. The switch and sponge were mounted
    such that when the sponge got wet and expanded, it pressed the leaf on
    the switch. Could be NC as well as NO.

    Can't remember if I saw it somewhere or if the image was drug-induced.
  4. Genome

    Genome Guest

    You am invited for suck my cock. It am very URGENT that you suck my cock

  5. Ken Taylor

    Ken Taylor Guest

    Unless you bought the cheapest possible alarm system, you should be able
    to program the inputs to be either normally open or normally closed.

  6. Macgyver

    Macgyver Guest

    Your question is a little confusing but it sounds like you want to use
    one of the alarm's reed switch sensors in a separate application as a
    water sensor. The simplest ways for you to change the logic of an open
    to a close (and vise-versa) = inversion, would be either using a relay
    or an inverting opamp circuit to provide the inversion. It really
    depends on what type of output the sensor has (sounds like dry contacts
    creating a circuit).
    More info on application, logic and voltage levels and the sensor is

    Is the reed switch switch sensing the water level using a floating

    Hopefully this is more helpful than Genome's advice.
  7. Fred Bloggs

    Fred Bloggs Guest

    If it works, then this is the simplest way:
    View in a fixed-width font such as
  8. Big House

    Big House Guest


    thank you very much. With a Vin of 12volts, would it be needed to add
    some resistor?

  9. Fred Bloggs

    Fred Bloggs Guest

    My *guess* is that the alarm already has a large internal pull-up
    resistor so no need to add one externally. That little circuit will
    limit itself anyway.
  10. Fred Bloggs

    Fred Bloggs Guest

    If the internal pull-up is not large enough (too much current), you gain
    things up like so:
    View in a fixed-width font such as Courier.
  11. Fred Bloggs

    Fred Bloggs Guest

    voops- snip

    View in a fixed-width font such as Courier.
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