I have posted wide varieties of small electronic projects on water level sensor in Circuits Gallery. This is another project for school students to detect the water level inside a water tank or any other water reservoir. We can call this as a ‘liquid level sensor’, because this circuit is able to sense the presence and absence of liquid in a tank.
This school electronic project is built around BC548 transistors and a 7432 OR gate IC. This water alarm will produce a beep sound when the water goes below a specified level (h1) or when the water overflows. This is one of the home science experiments that can be implemented as science projects for high school students.
You may also like to have a look at our other science experiments like automatic water tank level controller and numeric water level indicator. I have also published an article to detect overflow of water using alarm.
This school electronic project is built around BC548 transistors and a 7432 OR gate IC. This water alarm will produce a beep sound when the water goes below a specified level (h1) or when the water overflows. This is one of the home science experiments that can be implemented as science projects for high school students.
You may also like to have a look at our other science experiments like automatic water tank level controller and numeric water level indicator. I have also published an article to detect overflow of water using alarm.
Circuit diagram of liquid level sensor
Components required
- Power supply (or 6V battery)
- Resistors (1kΩ x 3; 100Ω x 3)
- Transistors (BC548 x 4)
- IC 7432 Buzzer
Working of water level detector
- The basic principle of this circuit is ‘switching property of NPN transistors’. That is when a transistor is ‘OFF’ its collector voltage is Vcc (6V) and when it is in ‘ON’ state the collector voltage falls to 0.02V (approx. 0V).
- 0.6V is required to turn ON a transistor (BC548). At normal condition Q1= OFF, Q2=ON and Q3=ON. Thus both inputs of ‘OR’ gate are zero..!
- We have dipped 3 wires in the water tank. 1 wire is from power supply and other 2 wires from the base terminals of Q2 and Q3.
- When water level goes below ‘h1’ the wire from transistor Q3 disconnects from the power supply, hence Q3 becomes ‘OFF’. Thus its collector voltage will be Vcc.
- This ‘high’ voltage is applied to the ‘OR gate (IC7432)’. Hence its output becomes high (if any one of the input of ‘OR’ gate is high, output will be ‘High’) and it leads to the turning ‘ON’ of the driver transistor Q4. Thus the buzzer produces a beep sound.
- When the water level goes above ‘h2’ Q1 becomes ON because its base terminal is energized by Vcc in the water, due to this Q2 will be in ‘OFF’ state. So the collector voltage of Q2 becomes ‘High’.
- Again this ‘High’ voltage is given to the OR gate making its output ‘High’ and it causes turning ‘ON’ of the driver transistor Q4. Buzzer will start producing sound.
Pinout of BC548 and IC 7432
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