Rain Alarm - LBM4

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Thursday, 20 June 2019

Rain Alarm

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.

rain alarm setup

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.
rain alarm sensor

This Rain Sensor is connected to the main circuit, so that the voltage should pass through this rain sensor’s wires. In normal conditions (if there is no rain), the resistance between the aluminum wires will be very high as a result there is no conduction between the wires. When it rains, water drops falls on the rain sensor, which decreases the resistance between the wires. As a result wires on the sensor sheet starts conducting and trigger the NE555 timer IC through the transistor circuitry. 

block diagram for working of rain alarm sensor

 Components Required

  1. 1 x Small Rain Sensor
  2. 1 x 555 Timer IC
  3. 1 x BC548 NPN Transistor
  4. 2 x 2N2222 NPN Transistor
  5. 1 x Bright White LED
  6. 1x 1N4007 PN Junction Diode
  7. 1 x 220 KΩ Resistor (1/4 Watt)
  8. 1 x 330 Ω Resistor (1/4 Watt)
  9. 1 x 10 KΩ Resistor (1/4 Watt)
  10. 1 x 470 KΩ Resistor (1/4 Watt)
  11. 2 x 3.3 KΩ Resistor (1/4 Watt)
  12. 1 x 68 KΩ Resistor (1/4 Watt)
  13. 1 x 22 µF Capacitor (Polarized)
  14. 2 x 100 µF Capacitor (Polarized)
  15. 1 x 10nF Ceramic Capacitor (Code – 103)
  16. 1 x 100pF Ceramic Capacitor (Code – 101)
  17. 1 x Buzzer (or Speaker – 8Ω)
  18. Connecting Wires
  19. Breadboard
  20. 12V Power Supply

 Working Principle

This is a simple project. Any electronics student or hobbyist can make this project without much effort. When there is rain, the Rain Sensor's wires start conducting. Since it is connected to the Rain Alarm’s circuit, the transistor Q1 will get turned ON and LED D1 starts glowing. At the same time Q2 will also be turned ON. When Q2 reaches its saturation state, the capacitor C1 will act as a short and make the transistor Q3 to be conducting. The RESET pin of 555 Timer IC is connected to the emitter of Q3. When Q3 reaches its saturation mode, it will assert the RESET pin of Timer IC to High or Positive.  As a result, it will generate a pulse in the OUT pin 3 of 555 Timer and make the speaker to produce alarm. The 555 Timer IC is configured to operate in astable mode.  A capacitor C4 is connected between the speaker and OUT pin3 of timer IC. This capacitor blocks the DC and unwanted components to the speaker.Depending on the time constant RC (R4, C1), after some time, the transistor Q3 will get in to cut off. The time period for the speaker to make sound is depends on the R4 and C1 values.

Circuit Diagram

rain alarm circuit diagram

  • 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.

About Rain 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.
rain alarm sensor
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.
rain alarm interal architecture

If there is no rain, the resistance between the contacts will be very high as there will be no conduction between the wires in the sensor.
If there is rain, the water drops will fall on the rain sensor, which will form a conductive path between the wires and it also decreases the resistance between the contacts.
As a result, the wires on the sensor board will conduct and trigger the NE555 timer through the transistors circuitry. Once NE555 is triggered, it will make the output pin high and which will make the buzzer to make alarm.


  1.  In the irrigation, it will detect the rain and immediately alert the farmer.
  2. In automobiles, when the rain detector detects the rain it will immediately active the wipers and inform the driver.
  3. In communications, it will boost the power of the antenna and increase the signal strength to send or receive the signals.
  4. In normal house hold, with the help of rain water detector we can automatically save the rain water. (This can be done only when home automation is done and there is proper equipment to save the rain water. In this, rain water detector will detect the rain and helps to switch ON the equipment which will automatically save rain water for different purposes).
  5. This can also be used if there is a chemical rain also. This is very common in industrial areas.


  1. good job keep on going

  2. really impressing

  3. Major Thanks for the blog post. Really thank you! Want more.
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  4. Wow! Such an amazing and helpful post this is. I really really love it. It's so good and so awesome. I am just amazed. I hope that you continue to do your work like this in the future also best alarm monitoring system