I guess it is a little difficult resetting this one:
http://www.pbase.com/sinoline/simple_moisture_sensor
But I am sure that could be worked out, because I have.

 

Of course water is probably all your basement will ever see, but think about long term reliablity and ease of testing, fewest components, etc. This kind of application can help save you a ton of $$ in damage and the the sensor portion needs to be as failsafe as you can come up with. I still vote the simple float switch if it was my basement. Basements are rare in California but sump alarms are common.

Now what I need is an earthquake alarm circuit that gives about 5 mins warning of a big one

Lefty

 

I trust my circuit. Besides, I'm living in an apt and my landlord didn't find it necessary to install an alarm, so I made one.

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Life is what you make it.

 

So if you don't have a sump pump; where do you find a float switch that operates in a (aprox) 0.01" of water? After all you do want an alarm that senses the very appearance of water.

 

Well never owning a basement, I don't know their normal drainage management. Is there no normal exit for water? If the floor is completely sealed then I guess one would need to find the lowest spot (unless non-slopped and perfectly level) and utilize something other then a float switch of course..

Lefty

 

Floats are more reliable than oxidizeable electrical contacts. Float activated relays are widely used in both industrial and home situations. We have several pumps at work that have built in floats for exactly this purpose. You just put them in a hole in the floor where water drains and give it enough space on all sides and as long as you check the mechanicals every 6 months to make sure nothing rusted or was blocked you never have to worry about it.

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Are you referring to the sensing contacts in the original circuit? They should not be subject to much humidity like a switch in a partial water filled hole.

 

If your float brings a magnet up to a glass enclosed reed switch, then there is no possibility of getting crud on the contacts.

 

I designed a detector for my brother last year using a mosfet. It was to monitor the basement sump level in the event the power went out.
One night, it was raining heavily and he heard the alarm downstairs, so he went to check on it. The float for the pump switch had stuck in the down position and the sump was nearly full.
It was $10 well spent (mostly on the case and 9v battery).
Jeff

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Nothing is impossible for the man who doesn't have to do it himself - Weiler's Law

 

ROLF, .01 inches? You can do better with humidity and temperature sensing in a known enviornment. physical contacts are a good backup, but no reliable enough on their own. Guess it goes to show no matter what the situation there is no single best responce, a mix of all of them are best to cover all ground.

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