Rain Alarm


The main objective of this project is to buzz an alarm when it detect rain water.

They are useful devices and play an important role in various industries such as automobile, irrigation, and wireless communication. Designing a rain alarm system is quite simple and we have designed here a demo rain alarm project with the help of 555 Timer IC.


  1. Rain sensor (Either you can purchase or build yourself)
  2. 555 Timer IC
  3. NPN Transistor BC547
  4. Resistors (470, 100k and 1k ohm)
  5. Capacitor (10uf)
  6. Buzzer
  7. Battery 9v


The main component of this rain alarm is rain sensor, you can either purchase one, or build it at home. It’s very easy to create a rain sensor. Take a sheet of Bakelite or mica, and paste the aluminum wire on it according to the diagram shown below. The Gap between the wires should be around 3-5mm. You can see that whenever the rain drop would fall on rain sensor, it will short the point A and B and a voltage would get applied on the base of Transistor, and it will be switched ON. We can also use copper wire for rain sensor but copper generally reacts to oxygen to form oxide, so it needs to be cleaned on regular basis.



It is a very simple rain alarm circuit which is designed using mainly a transistor, water sensor and a 555 timer IC. Whenever there is a rain, rain drops falls on the rain sensor, and as you can see in the diagram of rain sensor, water on rain sensor would short the Point A and B. As soon as Point A and B become short, a positive voltage would get applied on the base of Transistor Q1, through the resistance R4. Because of the voltage at the base, transistor becomes ON (initially it was in OFF state), and current started flowing form collector to emitter.

Now Reset PIN 4 of the 555 Timer, gets a positive voltage and 555 timer IC becomes ON and Buzzer starts beeping. Here we should note that initially there was no positive voltage at Reset PIN 4 of 555 IC, as it was connected to the ground through resistance R5 (4.7k) and 555 IC only works when Reset pin gets positive voltage.

Here we can see that 555 Timer IC has been configured in A stable mode so that Buzzer generate an oscillating sound (means periodically on and off). This oscillation frequency can be controlled by changing the value of resistor R2 and/or capacitor C1. Pin 5 control Pin, should be connected to ground through a .01uf capacitor. Resistor R3 and R4 has been used to control the transistor’s collector and base current respectively.

Rain sensor should be kept at 30-40 degree from the ground, so that water cannot stay on it, for the long time, this will prevent the alarm to going on for a long time.

We will be happy to hear your thoughts

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Majju PK
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