joecool85

I have it all working now, simple and works perfect.

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Sceadwian

The circuit will work fine to start, but long term use poses problems. The electrodes will build up an oxide layer, or a sludge (hard water or other sollution impurities) So will require cleaning on a frequent basis to sustain any kind of reliability.

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joecool85

Sort of, ideally it will never be submerged. I'm putting mine next to my sump pump, and unless I have a sump failure (it does happen every so often) they won't get wet. But the few times they do shouldn't create a lot of corrosion. Also, even with corrosion, this circuit should function fine as it isn't horribly critical what the resistance is between the two probes as long as there is some. I tried it with filtered water from the sink and it worked still! Heck, even moist fingers set it off.

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Sceadwian

Electrodes, especially copper still corrode in air, at the very least it should be suggested that the leads should be tinned, or preferably gold electrodes. My work environment is massivly corrosive (even ambient air) so something like this would have to be cleaned every day.

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mneary

Most of us know what you actually intend, but:

The emitter should not be connected to "ground". It should be shown connected to the negative terminal of the supply (battery), which in the practical application should not be grounded.

mneary

I don't know what your impurities are, but at copper.org, they say copper oxide is a conductor. [edit] Sometimes it's used as a semiconductor, and at extremely low temperatures it's a superconductor. [/edit] Since this circuit will trigger when the electrode resistance is megohms, I don't see daily cleaning needed in a basement or cellar.

More likely they will need occasional cleaning because dust, mold, and insects could cause false triggers.

joecool85

I don't see dust or insects causing a false positive, but I suppose mold could eventually. The circuit itself is good though. I'm using stainless steel for my probes, I doubt I'll ever really need to clean them.

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TheVictim

It is also conceivable that the electrodes could oxidize over time without any contact with water and present enough resistance when wet that the transistor would not have enough base-to-emitter voltage to be in an active state. Having a bias on the transistor would then require you need more circuitry to determine a trigger threshold. Once again simplicity would have to be sacrificed for reliability.

Sceadwian

Pass the tips of your electrodes through a lighter flame to add a little carbon, see if it still works.

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Nicksan

Does this circuit work on a breadboard?
I just tried it and nothing, except the piezo kept going off, I checked it and made sure the Transistor was good and still nothing.

Hero999

Have you check you're connecting it up correctly?

Is there any mositure residue on the breadboard?

Try drying it with a hair dryer, it might have condensation or sweat from your fingers on the board.

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Gaston

why not just use a float with a mechanical switch? it seems like that would be the simplest and most reliable

joecool85

Flip your transistor around, sounds like you may have it in backwards.

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Leftyretro

I have seen many methods of detecting liquid level in sumps working in a large refinery. The most reliable I've seen is a mercury switch mounted inside a rubber oblong bulb about 3" in diameter and 5" long. When liquid is below the bulb it hangs straight and stays an open circuit. When floating it would turn on it's side and close it's contacts. The problem with direct electrical probe type detectors is that we sometimes get oil and other hydrocarbons instead of water at other times, so we can't count of the dielectric or resistance properties of all the possible liquids.

Some time we use two such float switches at different levels to start and stop sump pumps to keep the sump level clear. Also a third even higher mounted float switch is used to generate a high priority alarm to let us know that there is a problem with either the pumps or too much liquid for them to keep up with.

Lefty

joecool85

While I agree about the floater being better for multiple fluid types, I designed this for water and only water. Hopefully that would be the only fluid flooding out my basement.

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