An astable multivibrator is wired around IC1 in this circuit (NE 555). The astable multivibrator’s operating frequency will be determined by the capacitor C1, the resistances R1, R2, and the resistance across the probes A&B. The probes will be open if there is no water up to them, therefore the multivibrator will not produce oscillations and the buzzer will not beep.
When the water reaches the level of the probes, some current will flow through the water, the circuit will be partially closed, and the IC will begin to produce oscillations at a frequency proportionate to the value of C1, R1, R2 and the resistance of water across the probes. When there is water up to the level of the sensing probes, the buzzer will beep.
Water Level Alarm Schematic Circuit Diagram:
- 4 – BC547 transistors.
- 6 – 220 ohm resistors.
- 3 – Colour LEDs – red, green, and yellow.
- 1 – Buzzer.
- 5 – 9v battery + battery clip.
- 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.