Activate LED when water not present

Discussion in 'The Projects Forum' started by srubino386, Feb 29, 2016.

  1. srubino386

    Thread Starter New Member

    Feb 29, 2016
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    Hey everyone

    So I am having trouble with this project of mine. Basically, I need an LED to turn on when water is not present (dries out). So first I need this to happen with just a bowl of water (oh and I cannot add salt at any point). Then need it to also work with a bowl of wet sand, bowl of wet paper towels, soil, etc. So I took a 9v and ran a copper wire at each end of the bowl and then to a 9v normally open relay, however it only works when the wires are touching, it's not conducting through the water. Then tried it with a 3v relay, same problem... Hmmm.

    Any help would be greatly appreciated!
     
  2. DNA Robotics

    Member

    Jun 13, 2014
    123
    26
    Until someone comes up with a better idea, do a web search for LM339 comparator circuits. I think it is sensitive enough. You may find a circuit that you can use. The output on or off depends on which input you use.
     
  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    While regular water does conduct electric current, it does not do it very well. The current through the water is not enough to do much of anything directly. The signal has to be amplified and compared against a reference voltage to determine if there is enough current to equate to the presence of water (or damp materials). Because passing DC through water causes electrolysis and other chemical reactions, the signal through the water usually is an AC signal, either a sinewave or square wave. This makes detection a bit more complex, but not much. The innergoogle has many circuits for water detection. Modifying one to reverse the action of the indicator is a minor change.

    ak
     
  4. Picbuster

    Member

    Dec 2, 2013
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    Simple problem use an alternating current like a block two advantages:
    a: no problem with electrolyse
    b: pure water acts like a bad capacitor so it has an impedance.
    take two metal bars one to gnd separate and isolate 1 cm approx.
    generate a block feed this via resistor and capacitor into a metal bar not connected to gnd.
    use opamp measure between resistor and capacitor.
    This is a measure for water level. that's all.
     
  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    You need to use an AC detection system like this...when water is present the led lights up, take the led from output to ground to make it on when no water detected.

    circuit

    Swap the opto-coupler for a led or transistor and relay.
     
    Last edited: Mar 22, 2016
  6. TheButtonThief

    Active Member

    Feb 26, 2011
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  7. srubino386

    Thread Starter New Member

    Feb 29, 2016
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    Thanks Dave,
    I've been trying to give this a shot and am still having trouble... I think this might be beyond my capability. Would you be able to walk me through this a little further? I hope we can work something out!

    Thanks again,
     
  8. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Ok what have you got done at the moment?
     
  9. ResFiber

    New Member

    Mar 9, 2016
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  10. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    The post #9 linked circuit uses DC energisation of the probes. That will result in relatively rapid corrosion of the probes. Dave's suggested circuit in post #5 is better.
     
  11. Dodgydave

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    Jun 22, 2012
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  12. srubino386

    Thread Starter New Member

    Feb 29, 2016
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    You know what, I'm not ready to give up just yet! Give me a few more days and I will get back to you....
     
  13. srubino386

    Thread Starter New Member

    Feb 29, 2016
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    Ok, I'm having trouble correctly placing everything in my breadboard... Ugh, I feel like I've tried this every which way now. My board goes from A-J, 0-60. Is there anyway you can help walk me through the placement of each item?
    Thanks!
     
  14. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Photo of your current layout...?

    ak
     
  15. Wendy

    Moderator

    Mar 24, 2008
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    Project : Pet Water Dish Alarm Sensor

    This is very close to what you describe.

    After 4 months I have noticed some corrosion on electrodes, thin wire used for picture hanging, but they still work. When I designed this I planned on replacing the electrodes periodically.
     
  16. srubino386

    Thread Starter New Member

    Feb 29, 2016
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    Alright so keep in mind I am new to bread boarding and electronics lol. Feel like I got about halfway there... Please help, and I apologize but I'm probably going to need very specific instructions...
     
  17. srubino386

    Thread Starter New Member

    Feb 29, 2016
    6
    0
    Thanks Dave
    So admittedly I haven't made it very far, I am obviously new to electronics but have posted a picture of where I'm at...
     
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