please HELP very important... water leakage sensor

Hello

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
opens).

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!!!

 

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.

 

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.

 

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

Ken

 

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
required.

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

Hopefully this is more helpful than Genome's advice.

 

If it works, then this is the simplest way:
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Courier.

 

Hello

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

Thanks

 

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.

 

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.

 

voops- snip

View in a fixed-width font such as Courier.