555 timer ic

Water Level Alarm Circuit Diagram


Here’s a simple water level alarm circuit diagram that utilizes a 555 timer to activate an audible alarm when the water level reaches a specific point. This circuit is relatively straightforward to assemble and can be powered by a 3V battery.

In this circuit, IC1 (NE 555) is configured as an astable multivibrator. The operating frequency of the astable multivibrator is determined by the values of capacitor C1, resistors R1 and R2, as well as the resistance between the probes A and B. If there is no water reaching the probes, they remain open, causing the multivibrator to remain inactive, and the buzzer remains silent.

However, when water reaches the level of the probes, a certain amount of current flows through the water, partially closing the circuit. As a result, IC1 starts producing oscillations at a frequency determined by the values of C1, R1, R2, and the resistance of the water between the probes. When the water reaches the level of the sensing probes, the buzzer sounds an alarm.

Water Level Alarm Schematic Circuit Diagram:

Components Required for Water Level Alarm Circuit

  • 4 – BC547 transistors.
  • 6 – 220 ohm resistors.
  • 3 – Colour LEDs – red, green, and yellow.
  • 1 – Buzzer.
  • 5 – 9v battery + battery clip.
  • Breadboard.


  • A 3V battery can be used to power the circuit.
  • Assemble the circuit on a high-quality PCB or a standard circuit board.
  • Two insulated copper Aluminum wires can be used to make the probes.
  • Place the probes in the area where you’ll be measuring the level.


  • The circuit is designed to indicate three levels of water stored in the tank: low but not empty, half and full but not overflowing.
  • When there is no water in the tank, all the LEDs are off as an indication that the tank is completely empty.
  • When water level increases and reaches M2, the contacts M1 and M2 get shorted as water acts as a conducting medium between M1 and M2.
  • This will turn on the transistor Q1 and the Green LED starts to glow. As the water level continues to rise and reaches half the tank, M3 will come into contact with water and receives a small voltage from M1.
  • As a result, Q2 is turned on and Yellow LED will glow. When the water in the tank rises to full tank, M4 is also shorted with M1 and both Q3 and Q4 will turn on.
  • The Red LED glows and also an alarm is made by the buzzer as an indication that the tank is full and the water pump or motor can be turned off.  

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