Rain Alarm Project

Rain water detector will detect the rain and make an alert; rain water detector is used in the irrigation field, home automation, communication, automobiles etc. Here is the simple and reliable circuit of rain water detector which can be constructed at low cost.

In this project, a simple Rain Alarm Circuit is designed, which, upon detecting rain, will activate a buzzer. Based on the buzzer, we can take necessary actions.

Components Required

  • 1 x Small Rain Sensor
  • 1 x 555 Timer IC
  • 1 x BC548 NPN Transistor
  • 2 x 2N2222 NPN Transistor
  • 1 x Bright White LED
  • 1x 1N4007 PN Junction Diode
  • 1 x 220 KΩ Resistor (1/4 Watt)
  • 1 x 330 Ω Resistor (1/4 Watt)
  • 1 x 10 KΩ Resistor (1/4 Watt)
  • 1 x 470 KΩ Resistor (1/4 Watt)
  • 2 x 3.3 KΩ Resistor (1/4 Watt)
  • 1 x 68 KΩ Resistor (1/4 Watt)
  • 1 x 22 µF Capacitor (Polarized)
  • 2 x 100 µF Capacitor (Polarized)
  • 1 x 10nF Ceramic Capacitor (Code – 103)
  • 1 x 100pF Ceramic Capacitor (Code – 101)
  • 1 x Buzzer (or Speaker – 8Ω)
  • Connecting Wires
  • Breadboard
  • 12V Power Supply

Working of the Circuit

We will see the working of the simple Rain Sensor Alarm Circuit Project. When rain falls on the sensor, the Aluminium Wires on the Sensor Board will start conducting and close the path between the supply and base of the transistor Q2.

As a result, the Transistor Q2 will turn ON, which will also turn ON the Transistor Q1. This will turn ON the Bright White LED connected to the emitter of the Transistor Q1.

When the transistor Q2 is saturated, the capacitor C1 will be shorted and will make the transistor Q3 to be turned ON. C1 will get charged by the resistor R4.

When the Transistor Q3 reaches the saturation mode, the Reset Pin of the 555 Timer IC, which is connected to the emitter of Q3, will be made positive.

The 555 timer is configured in Astable Mode. As the Reset pin of the 555 Timer IC is given positive voltage, it becomes active and we will get a Pulse signal at the output pin 3 of the 555 Timer IC. This will turn ON the buzzer and the alarm is activated.

If you are using a speaker, Capacitor C4, which is connected in between the Pin 3 of 555 timer and the speaker, will block the DC signal and allows only the variations in the signal which makes the speaker to make sound. The diode D1 will not allow any reverse current from the timer.

Because of the resistor R4 and capacitor C1, when the capacitor is completely charged, the transistor Q3 will get in to cut – off mode after sometime.

As a result, the Reset pin of the 555 Timer IC will not receive any positive voltage and the speaker will stop making sound. The time for 555 Timer to make speaker sound depends on the values of C1 and R4.

When there is no rain, the aluminium wire on the sensor will not conduct as they do not have any conduction path (open circuit). As a result, the sensor cannot trigger the 555 Timer IC and there will be no alarm.


  • Rain-Alarm-ProjecT-Circuit-Diagram

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