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Water Sensor Switch and Pump

Discussion in 'Sensors and Actuators' started by Chris Edwards, Oct 9, 2014.

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  1. Chris Edwards

    Chris Edwards

    Oct 9, 2014

    I am trying to create a bilge pump for my boat that draws out every last bit of water. Basically I want it to run a small plastic hose to the lowest point in the bilge then every few hours have a pump run and if the pump picks up water, maybe a vacuum, then it runs till the water is cleared. Any ideas would be great!


    Chris Edwards
  2. Gryd3


    Jun 25, 2014
    There are different sensors you can use. At what level would you consider the boat to be 'empty', does the pump you plan to use need to be primed, or will sucking air be ok.
  3. Chris Edwards

    Chris Edwards

    Oct 9, 2014
    Not sure, I would rather use a pump that can run dry.
  4. Gryd3


    Jun 25, 2014
    The difference will allow you to get almost the last drop.
    You could use a float switch, but that may not allow the water to go quite so low as dry.
    Using metal contact as a 'moisture' detector could work, but will oxidize and eventually the probes will need to be replaced.
    Once the sensor and pump are picked out, the electronics are the easy part because you can make then do whatever you need.
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    Nov 28, 2011
    A small DC pump will draw measurably less current when it's trying to pump air than when it's pumping water. You could use that to detect when there's no more water to suck. You would need to use a pump that will suck water even when it's currently full of air (I guess that's what Gryd3 means by "self-priming").

    So, every two hours, you start the pump and force it to run for long enough to prime itself and start pumping water, if there is any. Then after that time is up, you monitor the pump current, and when it drops below a certain threshold (meaning that it's no longer pumping water), you turn it off, and wait for the next two hours.

    A delay of two hours is too long to generate using a 555, which is the standard IC (integrated circuit - silicon chip) used for simple timing projects.

    One option would be a circuit using about three ICs - one long-duration timer, one logic IC, and one comparator IC to measure the pump current. Plus various small components, of course.

    In terms of circuitry simplicity, and design flexibility, a small microcontroller would be ideal, but that requires programming. If you're interested in going that way, a PICAXE might be a good option. See I can draw up a schematic and write you some starter code, but you would have to be able to understand it so you could check, debug, and enhance it.
    Gryd3 likes this.
  6. KMoffett


    Jan 21, 2009
    KrisBlueNZ likes this.
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