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Trying to find a water level sensor/switch

  1. Jan 17, 2014 #1
    Hello all. I am trying to find a sensor (probably switch is a better word) that will output a HIGH or LOW depending if the water (say, in a tank) has reached a certain level. I first googled: pressure sensor, then pressure switch. I also stumbled upon water level sensors, and now I am kind of confused.

    I searched for some on amazon, this is what I found:

    These contraptions don't make sense to me, I can only see two wires, GND and VIN, where is the output wire?

    Any help will be appreciated. Thanks.
  2. jcsd
  3. Jan 18, 2014 #2


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    The switches have a single contact. You can connect the switch with a twisted pair of wires. One of those wires will be connected to ground, the other is the signal. If the signal is going to a micro-controller input then you will need a pull-up resistor or a programmed bias current on that input to make the voltage high when the sensor switch is open.
  4. Jan 18, 2014 #3


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  5. Jan 18, 2014 #4


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    The level sensors linked in the OP appear to have an external moving magnet and a fixed sealed magnetic reed switch. There are other methods of determining fluid level that do not have external moving parts in contact with the fluid.

    To select an appropriate sensor requires knowledge of several of things.
    1. What will the level sensor's electrical output be connected to ?
    2. What fluid is the sensor being used to measure ?
    3. What unusual environmental problems like waves, ice or cattle may be present ?
  6. Jan 21, 2014 #5
    Thank you for the great replies and sorry for my late one. So if my understanding is correct, the level switches in the OP only require a ground? The other wire is the signal? Also, the description of these switches say that the max switch voltage is 100V, I want to know how much voltage I need to supply it with (but then again, If my initial logic is correct, I only need to supply it with ground... Now i am really lost).

    I think first I need to find an appropriate switch then I need to figure out how it works. So first, as Baluncore has mentioned, a couple of things worth mentioning:

    1. A micro controller (specifically a arduino nano)
    2. Water (H2O)
    3. None (a controlled environment... a water tank)
    *. Outputs HIGH/LOW (not pressure value)
    *. Low power (kind of obvious)
  7. Jan 21, 2014 #6


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    Attach a twisted pair of wires to the two terminals on your float switch. At the Arduino, connect one wire to the digital ground. Connect the other wire to your Arduino logic input. Place a 10k resistor between the signal pin and +Vcc.

    When the float switch contacts are open the input will be high, +5V. No power will be consumed.
    When the float switch contacts are closed the input will be low, 0V. Half a milliwatt will be dissipated in the resistor.
  8. Jan 28, 2014 #7
    Ok that makes a lot of sense. Thank you.
  9. Jun 13, 2014 #8
    Hey perplexabot,

    Although I personally am not as technically savy as some, I may know of a sensor that will help you. I have been using this water level sensor in my aquarium at home, and although I don't understand "how" it works, it seems to work pretty well, at least for my needs. It can actually tell me how much water is in the tank and shuts off the pump when the water reaches a certain level. Here's the link:
    Hope this helps!
  10. Jun 15, 2014 #9
    Hey, thanks for your help. I have actually finished this project a while back, I appreciate your input though.
  11. Jun 18, 2014 #10

    jim hardy

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    Note to next guy

    go to a junkyard and look under the hood of any modestly fancy automobile. Find the "windshield washer fluid reservoir" , most of them have a level sensing switch to illuminate the "Low Wash" light on instrument cluster. Should cost you about a dollar.
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