# Water Activated Alarm

Discussion in 'Electronic Projects' started by ElectroMaster, Jul 24, 2002.

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1. ### WillbeNew Member

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You're on.

-100 M makes me think current source.
-To get decent current through 100 M needs ~ 100 V.
-100 V is way higher than the base-emitter drop of a transistor so again I think Ideal Current Source.
-My old summary sheet from Teledyne Philbrick shows a I to V convertor where Eout = -Iin*R. For Eout ~15 V and negative Iin of 1 uA, R needs to be about 15 M, but since my doorbell xformer voltage doubler only puts out about 80 V this R has to be slightly bigger.
-The lightly loaded wall transformer puts out maybe 20% more than the rated 12 V, so size the LED driver resistor at (15 -2)/20 mA = 650, so use 680. 13^2 = 169 over 680 = ~1/4 W so use 1/2 W.
-You may need a decoupling cap, C1. It's good practice.
-You may also want to ground, either through a resistor or with a wire, all six unused opamp inputs.
-If you add a 1 M resistor in series with the WATER terminals this circuit will be much hardier.
-For the opamp output to swing positive the current has to be leaving terminal 2 so the doubler puts out a negative voltage.
-Re: the upstream post, the info I got from my 1988 summary sheet was the input bias current of the 324 was << 1 uA, but you may want to look into this. It should be << 1 uA, but accuracy in this case is not really important since the resistivity of even stinky air is probably >>> 100 M.
-C2 needs the + terminal to the right, if capacitors this small even need a polarity.
-Both AC sources go, of course, to the same wall plug.
-If the LED is dim because of high ambient lighting put it into a short section of heat shrink tubing.
-If you take any of this seriously you may want to build a test resistor from 5 ea. 20 M resistors. If you want to switch this in and out with a button, at 1 uA this might be "dry circuit switching", but you do have 80 V to wipe the switch contacts clean, so maybe a low current switch will actually work in this application.

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Last edited by Willbe; Today at 09:27 PM.

Last edited: Sep 11, 2008
2. ### RolfMember

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Easy to Detect Optically.........

It should be easy to detect optically because of the difference in the refractive index of water versus the plastic or glass container. If the container is metal it would be easiest to use a sight glass.

This can be easily done with a laser pointer and a photo diode; with the proper amplification.

3. ### kpelec318New Member

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hey i tried this one out with a CD 4o66 CMOS
i tried it practically , it doesnt work with water , however when i short the terminals it works . iam new to this site .so can anyone pls help me ?

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6. ### wink-sinkNew Member

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Hello guys good day....
I have my project proposed related to that... I'm a Electronics student..
It's entitled automatic sprinkler...

This is the part of the circuit:

http://www.zen22142.zen.co.uk/Circuits/Switching/waterrelay.gif

Any suggestions to improve it, @ Sir audioguru...Can you give me some advice to improve it to be more sensitive as you suggest on the water activated alarm?..

Thanks and GODBLESS!..

7. ### audioguruWell-Known MemberMost Helpful Member

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The sensitivity of the circuit depends on the hFE of the transistors. A BC108C is selected for high gain.
The sensitivity also depends on the amount of current needed for the relay coil. A low current coil will make the circuit more sensitive.
The sensitivity also depends on the amount of surface area of the probes in the water and their spacing.

8. ### 3333New Member

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[MODNOTE]Deleted Rubbish[/MODNOTE]

Last edited by a moderator: Jun 26, 2013
9. ### michaelboyNew Member

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Does anyone has a true and real circuit on this project ....show it !