Water tank overflow liquid level sensor alarm circuit is a simple electronics project for school students. In the previous articles we had discussed about numeric water level indicator and water level controller circuit ,but those circuits are much complex and are advanced projects for engineering students. The circuit schematic for water tank over flow alarm is shown below. It produces a beep sound when the water tank is completely filled by water.The advantage of this project circuit is that it saves water from accidental over flow. The circuit simply consists of a liquid (water) level sensor or water level detector with BC547 transistors. Any electronics hobbyist can implement this circuit at your home or work places at a cheap rate ($0.5). The heart of this water over flow circuit is the transistor switching part. So this circuit always prevents the wastage of water when you forget to switch OFF the motor pump set after switch ON.
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Circuit Diagram of water tank level alarm
- Power supply
- Resistors ¼ Watt (1kΩ x1, 100Ω x2)
- Transistors (BC 547 x 2)
- 6V Buzzer
- Water over flow from a tank or reservoir is detected using this simple project circuit. Firstly close the switch SW to turn ON the device.
- Initially the potential at point A in the circuit is Vcc, so the transistor Q1 remains in ON state (Read transistor act as a digital switch) and its collector voltage at Vce sat (0.02V).
- The collector voltage of Q1 is fed to the base terminal of transistor Q2 via100Ω resistor.
- 0.02V is not sufficient to turn ON the transistor Q2, hence it remains in OFF state and the buzzer will not produce any sound.
- A connection from ground is dipped in the water reservoir. When water level rises, the ground comes in contact with the base terminal of transistor Q1. Thus it changes to OFF state and the collector voltage rises to Vcc.
- The high voltage at the collector of Q1 turns ON the transistor Q2 since this high voltage is connected to the base of transistor Q2, then a current flow occur though the buzzer circuit and it produces beep alarm sound. (Read transistor act as a load switch)
- See the simulation window below, here instead of buzzer circuit we have used a LED for simulation. The switch ON is similar to water touching the point A.
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Simulation of water tank level sensor alarm
BC 547 transistor pin out