Rain Alarm Circuit Using Two Transistors

In this tutorial, I will show you a rain alarm circuit with an easy tutorial. This is very useful for home use because it alerts us whenever the rainwater falls on the two probes which are connected to NPN and PNP transistor, the rain alarm circuit will turn on and the buzzer will start to beep.

Circuit Diagram

rain alarm circuit

Components Required

  • BC548
  • BC558
  • 10 KΩ Resistor
  • 330 KΩ Resistor
  • 0.1uF Ceramic Capacitor
  • Buzzer
  • Connecting Wires
  • 9V Battery
  • Breadboard

Circuit Connection

To build the circuit connection of the rain alarm circuit at first, we need to place the transistors (i.e BC548 & BC558) on the breadboard.

Now it’s time to connect a 330 KΩ resistor in the emitter terminal of the PNP transistor and the other end of the resistor is connected to an open-ended wire.

Connect a 0.1uF capacitor and a 10 KΩ resistor on the collector of the PNP transistor. We have used a resistor and a capacitor in series so that it causes the first transistor to turn on and off followed by the second.

Now, in order to indicate the rain, we are connecting a buzzer. The positive side is connected to the collector of the PNP transistor and the negative side is connected to the emitter of the NPN transistor. Here the collector of BC548 transistor is connected to the base of the BC558 transistor.

Here we need a 9V power supply. Connect the positive end to the emitter of the PNP transistor and the negative to the emitter of the NPN transistor. And also connect a probe to the base of the NPN transistor.

Working of Rain Alarm

We all know that water is a decent conduit of power. By this principle of rain alarm circuit, the contact between two wires takes place and a current starts flowing towards the base of the NPN transistor. Since the collector of the NPN transistor is connected to the base of the PNP transistor. When the NPN transistor starts to conduct, the PNP transistor will also start conducting.

Thus the whole circuit will turn on and the buzzer starts to beeping.

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