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What I want is something that detects the presence of water, and sends a signal. It will be used to detect when the main drain in the basement gets clogged so that I can take preventative measures before it gets out of control. Ideally this switch could be interface from my computer via USB, and I can then program it to send me an email when it goes off.

EDIT:

I am not looking for a canned product that costs in excess of $100! I am not an electrician, but I am a computer programmer and I want to be able to do all of that part on my own. There has to be some kind of low-level sensor out there that I can hook up how I want. There ought to be various ways to intercept the signal from said sensor. Once I have a sensor and a way to read the signal from it, my possibilities are endless. I am just trying to get to that point and I have no clue where to begin.

There are 25+ year old sprinkler systems out there that are smart enough to not go off when it rains. I asked a local irrigation expert who installs and maintains these systems, and he says the old ones have an analog sensor that you typically mount on the roof, it contains some kind of rubber element that swells up when it gets wet. The swelling causes it to press a button. When the water evaporates, the swelling goes away and the switch gets flipped again. Now that is old school and certainly not rocket science, but I have no clue how to devise such a thing. That is why I am here.

I have answered a lot of questions on Stack Overflow because that is my area of expertise, just trying to get some love back here in an area where I am clueless!

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closed as off-topic by Tester101 Jun 16 at 9:58

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1  
I have thought about using a fishing bobber to hit some electrical function above it. I like the question. The issue that I see is needing some relay or "computer" close-by to send the "email". And of course that isn't usually a good spot for those things. Really good question. –  DMoore Jun 13 at 18:59

3 Answers 3

What you want is a float switch. They make small ones (had one to turn off the AC if too much water was in the tray) but never seen one for USB. But you can easily wire one to switch on a warning light or a buzzer.

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Makes sense for a small area, but is not even close to practical for detecting minuscule amounts of water across a large level area. In my case I am going to require more precision. –  Josh Stodola Jun 24 at 0:12
    
Just a thought, try making a contact switch with a dried out sponge. Use a low voltage circuit, have one of the contact plates on the sponge and other mounted above it. A small amount of moisture should rehydrate the sponge causing it to expand and then close the circuit. –  diceless Jun 26 at 5:32

Detecting water is actually a harder problem that you might think, depending what you want. A float switch will only indicate that there are big problems already well-advanced, since it needs an appreciable amount of water to go off. On the other hand, switches that try to detect the conductivity of a film of water on the floor are often problematic due to contamination by dirt and the dried reside of pervious flood events.

Once sensed, converting to USB becomes a shopping question (or the whole thing is a shopping question, and shopping questions are off-topic.) You basically need an interface that can detect a switch closure or voltage level - generally, an input/output board (or perhaps only an input for this) board.

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This might be a little more of a project than you were really thinking of, but if what you really want is to be notified via 'the internet' when there is water in a location, look into some of the home automation technologies like Z-wave:

http://www.smarthome.com/2852-222/INSTEON-Leak-Sensor/p.aspx http://www.everspring.com/ST812.aspx

They separate the sensor part and the 'smart' part into separate systems and while it may be overkill for your exact needs, it's probably easier to get the individual parts doing what you want.

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That is truly awesome but I was wanting to do much of the work myself. I don't have a couple hundred bucks lying around. I just want a sensor and some knowledge on ways to intercept the signal from it. I am not an electrician I am a computer programmer. –  Josh Stodola Jun 24 at 0:00
    
If you want to make it even more bare bones you'll need to move to something like Arduino or Spark - www.spark.io –  Aaron Jun 24 at 15:29

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