Low liquid alarm

Discussion in 'The Projects Forum' started by 5eon, Sep 19, 2012.

  1. 5eon

    Thread Starter New Member

    Sep 19, 2012
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    Have built this simple low liquid alarm as attatched-my problem is when probes are in the liquid the buzzer is still sounding albeit at low level. It is working as when the liquid level drops the buzzer goes loud but how can I make it silent when liquid is present? I know this is all very basic but hey I've got to start somewhere.
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    Where did you get this circuit from? There are some wrong assumptions made here.

    A lot depends on the electrical conductivity of the liquid.
    Ordinary tap water is not a very good conductor of electricity. The 1kΩ pullup resistor is way too low in value for this circuit to work.

    You will need two stages. One stage to detect the liquid and the second stage to drive the buzzer.
     
  3. 5eon

    Thread Starter New Member

    Sep 19, 2012
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    OK MrChips, Thanks for your prompt reply. Circuit was from the website shown on the attatchment, any idea where to get a better one?
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Last edited: Sep 19, 2012
  5. 5eon

    Thread Starter New Member

    Sep 19, 2012
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    Hope I'm not being stupid here, but I want to detect lack of liquid not prescence.
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
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  7. 5eon

    Thread Starter New Member

    Sep 19, 2012
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    Thanks DodgyDave
     
  8. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    You didn't state the purpose of you water system, but using direct current between long-term, submerged electrodes will cause the electrodes to corrode.

    Ken
     
  9. ScottWang

    Moderator

    Aug 23, 2012
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    Maybe you can add a Zener between 100Ω and transistor, this can be increase the Voltage detect level, and also increase 100Ω to 1K~5K, it depends on how do you use the value of Zener, and how many current does the Buz needed.

    If you want to detect the water, the resistance of water maybe over 10K, you better use 2 transistors to do the detection job.
     
  10. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Decades ago I built a water sensor for my Mom (she liked to hang the clothes outside to dry). Just a quad CMOS NOR or NAND gate, 2 gates as a gated astable, 1 gate to detect the water, and I dunno what the last gate did (maybe needed an inverter?). The astable output drove an NPN transistor to squalk a speaker.

    The thing ran for years and years off the original 9V battery,

    Sensor input was a gate input with something like a 1M pull down resistor, other probe was the 9V with a series 100K resistor.
     
  11. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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