Security & Saftey

Rain Alarm Project

Rain Alarm Project is a simple but very useful project that detects Rain (Rain Water) and automatically triggers an alarm or buzzer.

Water is a basic need in every one’s life. Saving water and proper usage of water is very important. Here is an easy project which will give the alarm when there is rain, so that we can make some actions for rain water harvesting and also save the rain water for using it later.

With the help of saving this rain water through rain water harvesting, we can increase the levels of underground water by using underwater recharge technique.

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


  • Circuit Diagram
  • Components Required
  • Rain Alarm Project Block Diagram
  • Rain Water Sensor
  • Working of the Circuit
  • Rain Alarm Project Circuit Applications:

Circuit Diagram

The circuit diagram from the Rain Alarm Project is shown in the below image.

Rain Alarm Project

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

Rain Alarm Project Block Diagram

The block diagram of the Rain Alarm Project is shown in the following image. The three main components of the project are the Rain Water Sensor, 555 Timer IC and Buzzer.

Block Diagram of Rain Water Detector

When the Rain Water Sensor detects the Rain, it sends a signal to the 555 Timer. The 555 Timer IC, which is configured in its Astable Mode, will then activate the Buzzer.

Rain Water Sensor

The Rain Water Sensor used in this project is shown in the image below. It is a simple sensor and it is an easy to use tool for detecting rain. It can act as a simple switch, where the switch is normally open and when there is rain, the switch closes.

Even though Rain Water sensor is the main component in the circuit. We need not to go and buy in the market or online. We can do it ourselves just by taking the piece of Bakelite or Mica board and aluminium wire.

Bakelite or Mica board should be made completely flat and aluminium wire should be pasted on the flat board as shown in the figure below. Care should be taken that there should be no spaces between the wire and board.

When the rain water sensor is completed, it should get connected to the circuit and voltage should be passed through the wires.

There will be no conduction between the wires in the sensor if there is no rain, thus the resistance between the contacts will be quite high.

When it rains, the water drops land on the rain sensor, forming a conductive route between the wires and lowering the resistance between the contacts.

As a result, the sensor board’s wires will conduct and trigger the NE555 timer via the transistor circuitry. When the NE555 is triggered, the output pin goes high, causing the buzzer to sound an alarm.

Working of the Circuit

We’ll look at how the Rain Sensor Alarm Circuit Project works. When rain falls on the sensor, the Aluminum Wires on the Sensor Board begin to conduct, closing the channel between the transistor Q2’s supply and base.

As a result, the Transistor Q2 will turn on, causing the Transistor Q1 to turn on as well. This will activate the Bright White LED attached to the Transistor Q1’s emitter.

The capacitor C1 will be shorted when the transistor Q2 is saturated, causing the transistor Q3 to switch on. The resistor R4 will charge the capacitor C1.

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

In Astable Mode, the 555 timer is set. When the 555 Timer IC’s Reset pin is supplied a positive voltage, it becomes active, and we get a Pulse signal at pin 3 of the 555 Timer IC. This will trigger the alarm and turn on the buzzer.

If you use a speaker, Capacitor C4, which is linked between the 555 timer’s Pin 3 and the speaker, will block the DC signal and allow only the signal changes that cause the speaker to make sound. The timer’s reverse current will be blocked by the diode D1.

Because of the resistor R4 and capacitor C1, the transistor Q3 will enter cut-off mode after a while when the capacitor is fully charged.

As a result, the 555 Timer IC’s Reset pin will not receive any positive power, and the speaker will cease to function. The time it takes for the 555 Timer to create a speaker sound is determined by C1 and R4 settings.

The aluminium wire on the sensor will not conduct if there is no rain because it lacks a conduction channel (open circuit). As a result, the sensor will not be able to trigger the 555 Timer IC, and no warning will be generated.


  • Rain senor should be kept in the open place at 30 to 40 degrees from the ground. As a result, rain water will not be present on the sensor for long time.
  • This circuit will automatically switch of the alarm after sometime and LED will glow continuously until the rain stops.

Rain Alarm Project Circuit Applications:

  1. It will detect rain in the irrigation system and notify the farmer promptly.
  2. When the rain detector in a car detects rain, the wipers are automatically activated and the driver is notified.
  3. It will improve the antenna’s power and increase the signal strength to broadcast or receive signals in communications.
  4. We can automatically preserve rain water in a typical household with the help of a rain water detector. (This can only be done if home automation has been completed and adequate rainwater collection equipment has been installed.) In this case, a rain water detector will detect rain and assist in turning on equipment that will save rain water for various reasons).
  5. This can also be used if there is a chemical rain also. This is very common in industrial areas.


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