Water Level Indicator

A water level indicator is a device used to detect the water level in any vessel. The device can be used to indicate water levels at various stages, and is very handy when installed in tanks, as it can prevent overflowing of water as water fills up in them.

The Circuit

There are mainly four parts of the circuit

  1. The Sensor : It is generally a fixed support inside the tank having some nuts and bolts with wires coming out.
  2. The Circuit : It comprises the brain of the module, where in all the various inputs from the sensors are fed. It is the unit from where you will get all the information of how much of water is in the tank.
  3. The Power Supply : It is the part where in you will be converting the A/C voltage to a regulated voltage of 5V to the Circuit.
  4. The Buzzer : It is responsible for bringing up the sound when the water level fills up in the tank. It will also be having a speaker or a buzzer to alert.

(Source : [http://www.instructables.com/id/Water-Level-Indicator-with-Alarm/?ALLSTEPS])

Devices used in the Circuit


List of components used


The LED's used for indicating the current water level are of various colors and resistances. Now, as the water starts to rise up, the sensors starts to get in contact with the water and the corresponding transistors are activated. There is a flow of current through the transistors, making the LED's light up. Here, there is a current-limiting resistor of 470 ohms between the transistor and the LED, to prevent excess current to pass through the LED.

  1. Red LED (Indicating no water in the tank as none of the sensors are in contact with the water)
  2. Red LED ( Level 1, indication of very less water in the tank )
  3. Yellow LED (Level 2, indication of less than 1/4th water)
    Float right
  4. Yellow LED (Level 3, indication of 1/4 of water in the tank)
  5. Green LED (Level 4, indication of half of water in the tank)
  6. Green LED (Level 5, indication of more than half of water)
  7. Green LED (Level 6, indication of nearing filling up the tank)
  8. White LED (Level 7, Full indication of tank and buzzer starts ringing)

There is one extra power LED without a transistor and that is because this LED will be telling us two things. Firstly when the circuit is switched on, it will be monitoring the power present in the unit and secondly it also indicates that there is no water present in the tank at all. As the water level is below the No. 1 (as shown in the circuit) sensor, no LED's will be lighting up, but only for the one LED.

BC547 transistor


The BC547 transistor acts as a switch which gets activated by the sensors. Actually, a transistor is just nothing more than a tiny switch, which is controlled via an electronic signal. There are 3 pins on a transistor: collector, base and emitter. If an electronic signal is passed through the base, the switch is open and electricity can flow through the emitter and the collector. Hence, when the sensors are in contact with water, current passes through the base, completing the circuit. In this way, the transistor acts as a switch for the various LEDs.


The buzzer is connected to the topmost LED and transistor, and hence works only when the tank is completely filled. It is the most important part of the circuit as it can be connected to another switch which will automatically turn the motor off when the buzzer goes off.


Voltage regulator (7805)

The circuit draws power from the mains power supply. This 220V supply is converted to DC by two diodes working in parallel, and further rectified by a capacitor. The final DC output is attained by using a 7805 voltage regulator along with a filtering capacitor for converting 220 V ac mains supply to 9 V dc supply, which scales down the DC voltage to 9V.


Connections and Working

Time for adding the LED's to the panel. Let's start by adding the Red LED from the bottom end. Then to the Yellow and Green and finally White. This LED should then be soldered to the PCB as shown in the circuit diagram. What we did was soldered directly to the PCB below the front panel, as it gave a solid base for the LED's.

Now fix the buzzer just beside the PCB and give the connection from the circuit board. Then also fix the power supply at the box with the help of nuts holding the transformer firmly to the box.


After making sure that all the things including LED's, transistors, resistances and the power supply are in place, take 7 wires and connect them to the circuit putting them to various levels in the container. As water is filled up to various levels the wires one by one come in contact with it and complete the circuit forcing the LED's to light up. Finally after the water is filled up to the brim the last LED glows white and the buzzer connected with it goes off indicating the maximum water level.

Testing of the Circuit

After the setup is complete we put the sensors in a container in which we gradually fill up water. Below are shown two stages of this process


The circuit was found to work in a bucket being filled up with water, and can also be extended for larger equipments such as tanks, simply by increasing the lengths of the sensing cables.

1: (Level 1) water is considerably low and pump needs to be started
2: (Level 2) water is low
3: (Level 3) Water level is 1/4
4: (Level 4) Water level is Half
5: Level 5) Water level is more than half
6: (Level 6) Water level is about to fill up
7: (Level 7) Water level has filled up and alarm starts to sound
8: Common Positive Pin


Thus finishes the installation of the device and test it by turning the device on and checking the water level in the tank. For testing just put the power on and you will see some of the LED's glowing, indicating the level of the tank, if you see only one of the RED glowing then your tank is fully empty and it is time you should turn on your water pump. After the pump is on you will then see after some period of time that the LED's will start to glow from bottom up till the final White LED will light up and sound up the alarm.

Links and References

  1. http://www.instructables.com/id/Water-Level-Indicator-with-Alarm/?ALLSTEPS
  2. datasheet of the transistor


Harshvardhan Kalra (2014043)

Ayush Agarwal (2014029)

Shantanu Jain (2014097)

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