Water Level Indicator with Microcontroller ..

Discussion in 'The Projects Forum' started by duck, Sep 6, 2010.

  1. duck

    Thread Starter New Member

    Sep 6, 2010
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    This is a circuit diagram I've taken from internet .. website <http://microcontroller51.blogspot.com/2010/03/microcontroller-at89c2051-8051-family.html>


    Which Nand Gate Optocoupler can I use ?? Please Help ..
     
  2. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    duck,

    Not sure how you're planning on using the indicator, but the DC current through sense electrodes will cause them to corrode from electrolysis. This is not a problem in sensors that only rarely touch the water (like for sump pump controllers), but a problem for electrodes that are continuously submerged and conducting DC current. Better designs use AC to drive the electrodes.

    Ken
     
    Last edited: Sep 6, 2010
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  3. SgtWookie

    Expert

    Jul 17, 2007
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    Along the same train of thought as Ken's, you can avoid having the electrodes exposed at all. Air has a dielectric constant just slightly greater than 1 (very, very slightly greater), and water has a dielectric constant of roughly 78.

    You could use a pair of single-sided copper-clad circuit boards that are conformal coated (think clear acrylic lacquer) that are held at a constant distance from each other using insulating spacers to create a home-made capacitor.

    If there is just air between the plates, its' capacitance value will be small. As the water level increases, coming between more of the plates' area, the value of capacitance will increase considerably.

    The capacitor could be used as the C part of an RC tank circuit, charged/discharged by one of the uC's I/O pins via a resistor.

    Use a comparator input to trigger and capture the number of clock cycles elapsed when the cap is around 2/3 to 4/5 charged.

    Since the plates are electrically insulated from the water in the tank, there is no need to use optoisolators, and only two I/O pins are needed for water level sensing.
     
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  4. duck

    Thread Starter New Member

    Sep 6, 2010
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    Alright .. Just that I'm not able to find the optocoupler given in this circuit ..
     
  5. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Have you tried to contact the blogger?

    Looks like the NAND function is irrelevant, since the external inputs are fixed high. You just need an opto-coupler with an inverted logic output, or an open-collector output with a pull-up resistor. Even the inverted output isn't required since it's just a logic level call in a program. So almost any opto-coupler with a low I(f) for the LED might work.

    Also, the conductivity of the water will be a big factor in whether it will work or not.

    Ken
     
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