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    water level sensor circuit for wireless monitoring

    Dear all
    Right now am involved in a project called wireless water level controlling / monitoring system..

    previously i designed wired water level controller its works good...

    but now planned to design wireless using low power RF

    one transceiver in tank and one in the motor side. The transceiver in the tank side is to be operated by a two duracell battery...

    now am in need help in designing low power water level sensing circuit using battery..

    thanks in advance!!!

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    Re: water level sensor circuit for wireless monitoring

    Hi,

    You know what they say - Ask a vague question, get a useless answer... ;) Low power: 1mA or 1nA per day or per year? Is it in a dark enclosure? It it for 1,000,000 litres or 50ml? etc.

    Anyway, the bulk of the current drawn is supplying the TLV431 with ~800uA. A reference with a lower supply current would be an idea, such as a resistive divider (but that would create a falling ref wrt battery voltage). The actual sensing circuit, which as you can see is just a variation on a very, very standard premise/design (the so-called "lie detector" aka "soil humidity sensor" aka "water level sensor" open or closed path to gnd or wherever the designer fancies), in simulations draws approximately 130uA to 170uA at 3V and will certainly work down to around 2.4V or lower. You could even dispense with the comparator, frankly but then have to spend time designing in battery voltage drop and ensuring Vbe and/or VOH is still attainable.

    Click image for larger version. 

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    I'm interested in seeing serious suggestions for a low power water level sensing circuit.

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    Hi,

    I'd thought of pressure sensor water level detecting too because I'd thought about avoiding corroding wires and so on, but at first glance it looks as though it is more complicated parts-wise and calculations-wise than a simple yes/no circuit really requires. e.g. Liquid-Level Monitoring Using a Pressure Sensor

    I simulated the above comparator circuit using a diode-connected NPN as the reference (instead of the TLV431) and it does use far less quiescent/housekeeping current and seemingly functions from 0º to 100ºC. Not sure I'd want to chance that sort of temperature-dependent reference unless I'd done some real testing first.

    Far more economical re quiescent current is the bjt trio seen in so many of these circuits. Looking at what I was simulating, I think it's better to have the output go low when the water level drops below whatever level as that way the bulk of the current is drawn then and not all the time just to let the user know that there is water above x level. As you appear to be using a PIC/MCU that's not an issue I guess as input levels and what they signify can be defined in the code. Two more simulation screenshots for comparison of this idea about minimising current draw with active high or active low signals:

    Click image for larger version. 

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    Re: water level sensor circuit for wireless monitoring

    hi d123 sorry for the late reply...
    i really appreciate your work...

    can we use capacitance method to sensing water level...
    here is the link.
    https://www.mdpi.com/1424-8220/11/5/4656/htm



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    Re: water level sensor circuit for wireless monitoring

    Hi,

    Well, evidently we can. There are a variety of capacitative moisture (soil humidity) sensors out there. Nice document you link to, a ready-made solution for you perhaps.

    I didn't know pure water is 20MOhms/cm3, tap water is ~2k5, "dirty" river water is maybe 200R, and seawater is ~30R... No wonder people add salt water to earth test points before getting their Megger results :).



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    Re: water level sensor circuit for wireless monitoring

    hi d123
    can we use the following circuit... i think it be easy....Click image for larger version. 

Name:	water-sensor-circuit-schematic-trigger-diy-enthusiasts-wiring.jpg 
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    Re: water level sensor circuit for wireless monitoring

    Hi,

    I don't know. It looks like a SR latch. May or may not be particularly reliable. You'd need to simulate and/or breadboard it to see how reliable its operation is. What does "two duracell battery" mean regarding supply voltage?



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    Re: water level sensor circuit for wireless monitoring

    It is an SR latch and it should work with some caveats:

    1. The water container must be electrically isolated, no other electrical connections (via metal pipes etc.) are allowed unless they are bonded to the "Common Probe".
    2. The ICs must be CMOS types (CD4000 series for example).
    3. There is a roughly 50% chance of the relay operating if the circuit is powered up when the tank is empty or above threshold level.

    As mentioned earlier, the circuit relies on electrical conduction through the water so its resistance must be fairly low. That largely depends on dissolved salts and it may not work at all if for example distilled water is used.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.



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    Re: water level sensor circuit for wireless monitoring

    Industry standard level control relays for electrodes have adjustable threshold range, e.g. 1k - 100k resistance. It's suitable for drinking water, but not for deionized water. The latter can use e.g. high frequent capacitive sensors. Level sensors shouldn't use DC voltage which causes electrolysis and electrode corrosion.



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