How to build a water level sensor

Written by steve aycock
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How to build a water level sensor
A water level sensor can be used to measure the water level in metal water tanks. (fire-prevention tanks with water image by YURY MARYUNIN from

A water level sensor can be used to monitor the water level in many applications, such as swimming pools, aquariums and industrial processes. Pressure sensors and electrical contact sensors are two types of devices that can be used to build a water level sensor. Sensor construction depends on the specific application details, such as water container size, sensor resolution and what type of signal is desired.

Skill level:

Things you need

  • Pressure transducer sensor or metal for contact sensors
  • Wire or cabling
  • Circuitry for receiving and responding to sensor signals

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  1. 1

    Select an appropriate pressure transducer for the weight range you wish to sense. Water weighs about 3.79 Kilogram per gallon, so you'll need a sensor that can measure the pressure (or weight) of the water tank (or container) when it is full.

  2. 2

    Build a circuit to receive and process the sensor signal. The circuit can be as simple as one that turns on a low-voltage indicator light when the pressure drops below a predetermined level or as complex as a microcontroller-based circuit to read the sensor signal and display or transmit the value. The circuit will need to be designed to receive and work with the voltage and current levels output by the transducer.

  3. 3

    Connect the pressure transducer to wire leads using solder or a mechanical connector. Use leads that are long enough to connect the transducer to location of the circuit handling the sensor signal.

  4. 4

    Attach the pressure transducer to the bottom exterior surface of your water container. Follow the transducer manufacturer's instructions for mounting the transducer.

  5. 5

    Connect the transducer leads to the circuit. Using breadboard, wire wrapping or solder, connect each lead of the transducer (typically two leads per transducer) to the circuit board that will be receiving the sensor signal.

  6. 6

    Test the water level sensor. Apply power to your water level sensor system and observe whether the sensor is working correctly. Change water levels to see whether the sensor responds appropriately. If there is no water level reading, check the electrical connections between the sensor and the circuit. If the water level reading is incorrect, you may need to adjust your circuit so that it is more accurately calibrated to the pressure transducer.

  1. 1

    Select the number of water level increments to be measured (also known as the resolution of the sensor). With an electrical (or contact) water level sensor, you'll have a pair of contacts for each water level increment. For example, if you wanted to measure the container in quarters, you'd need three contacts representing 1/4, 1/2 and 3/4 full.

  2. 2

    Create a pair of contacts for each level. The contact can be as simple as two pieces of metal mounted in close proximity to each other such that immersing the contact in water will permit an electrical current to flow between pieces of metal. Be sure to use a metal that won't quickly corrode when exposed to water, such as aluminium.

  3. 3

    Connect each pair of contacts to wire leads. Use solder or a mechanical coupler to connect the contacts to the leads. For each contact you'll have two wire leads. Make sure to cut your leads long enough to extend out of the water container and reach your circuit. Also, make sure that the connection points between the leads and the contact sensor are sealed.

  4. 4

    Mount each pair of contacts at the appropriate location in the tank. Use an appropriate fastener such as a bolt or waterproof adhesive to mount the contacts. For example, if you are sensing quarter tanks, mount a contact at each of the 1/4, 1/2 and 3/4 tank levels.

  5. 5

    Build a circuit to receive and respond to signals from the contacts. This circuit can be as simple as one in which the contacts act as switches to turn on low-voltage indicator lights (such as LEDs) when the contacts are exposed to water. The circuit could have a row of lights that indicate the water level in the tank ranging from full to empty. To prevent electrical shock, be sure to use a circuit that supplies a low voltage and current to the contact sensors.

  6. 6

    Connect the contact leads to the circuit. Using breadboard, wire wrap or solder, connect the wire leads from the contacts to the circuit board.

  7. 7

    Test the contact water sensor. Power up your sensor and observe the output of the circuit. Change the water level in the container and verify that the circuit output changes accordingly. If you do not get correct water level readings, check the electrical connections between the contact sensors and the circuit.

Tips and warnings

  • Use caution when working around water with electrical equipment. Be sure you know what connections are made before turning on the power. Also, be sure not to touch the water when energising your sensor for the first time.

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