I need t make a simple water (moisture) sensor to connect to a talking catfish plaque.

I have a concrete basement (swimming pool style) no drains or sump pump. Its below ground level so no where for the water to go ! So if my boiler blows or leaks I will have a very ugly swimming pool. And all my workshop will be floating. I have this cool talking catfish plaque. Its 6VDC batteries and a Transformer for AC plug in power.  I need a simple switch to activate the plaque. I tried two wires from the switch it has , put in water, no luck. I tried the alum. foil type posted instruct. that does not work either. So any suggs.? Thanks Simple is better. I can solder and read simple scematic .stuff. But KISS.

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orksecurity6 years ago
The simplest I've ever seen: Take a knife switch (available from hardware store), wrap a rubber band around it to hold it closed (on), then use a piece of effervescent tablet (available from the drugstore -- headache remedy, denture cleaner, anything which fizzes when you drop it into water) to hold the switch open.

Water hits the scrap of tablet, it rapidly crumbles, switch closes and your alarm goes off. Obviously, you have to reset it manually by drying it off and inserting another tablet.
You could do that easier with 2 brass drawing pins. Stick them into a bit of wood opposite each other separated by anything that will dissolve in water and wrap the band round the whole parcel. Saves the cost and difficulty of getting a knife switch.
triumphman (author)  rickharris6 years ago
Now that is what I am looking for , simple, yet reliable, and I can still use the catfish to alert me of a leaky furnace. Thanks. I'm going to tryit tonight.
AND? did it work? Next the Instructable? ;-)
Oh, that's clever!
Can't really take credit for it -- I think I swiped it from PopSci or PopTronics or one of those, decades ago.
Sorry my reply looks like it took away your credit.
Is this system intended to be an alarm to alert you that your basement is filling with water? If so, why use such a whimsical method as a talking fish for such a serious event?

Anyway, it sounds like you were trying to pass the power supply current to the plaque through the wires in water and foil switch that did not produce the desired results. Those methods should work for detecting moisture, but they would then in turn activate a switch that could handle the larger current needed for the plaque.

You could build a simple circuit consisting of just an NPN transistor and a resistor. The transistor would then turn on to allow complete the circuit to ground for the power supply. So, instead of conencting the ground from the power supply directly to the plaque, it would connect to the collector of the transistor, and the emitter of the transistor would be connected to the power supply ground lead. The base would be connected to the positive lead of the power supply, through the moisture switch and a resistor. The foil switch would allow current to flow into the base of the transistor when it was in water, thus turning on the transistor. A value of 1k might work well for the resistor, and any NPN transistor that can continously handle 500mA should work ok. (I don't know the exact current draw of the plaque).

Another method would be using a float switch. Some sump pumps come with them. One downside to that approach is that enough water would need to accumulate to lift the float enough to turn on the switch. By that point, there may already be substantial damage to your basement or its contents.
triumphman (author)  LargeMouthBass6 years ago
Not simple enough for me! Too much info for me to follow. Thanks for trying!