Rain Sensor working principle Example and applications

 Rain Sensor

What is a Rain Sensor?

A rain sensor is one kind of switching device which is used to detect the rainfall. It works like a switch and the working principle of this sensor is, whenever there is rain, the switch will be normally closed.

Rain Sensor Module

The rain sensor module/board is shown below. Basically, this board includes nickel coated lines and it works on the resistance principle. This sensor module permits to gauge moisture through analog output pins & it gives a digital output while moisture threshold surpasses.

 This module is similar to the LM393 IC because it includes the electronic module as well as a PCB. Here PCB is used to collect the raindrops. When the rain falls on the board, then it creates a parallel resistance path to calculate through the operational amplifier.

This sensor is a resistive dipole, and based on the moisture only it shows the resistance. For example, it shows more resistance when it is dry and shows less resistance when it is wet.

Pin Configuration

The pin configuration of this sensor is shown below. This sensor includes four pins which include the following.

  • Pin1 (VCC): It is a 5V DC pin
  • Pin2 (GND): it is a GND (ground) pin
  • Pin3 (DO): It is a low/ high output pin
  • Pin4 (AO): It is an analog output pin

How Rain Sensor works?

The working of the rain sensor is pretty straightforward.The sensing pad with series of exposed copper traces, together acts as a variable resistor (just like a potentiometer) whose resistance varies according to the amount of water on its surface.

This resistance is inversely proportional to the amount of water:

  • The more water on the surface means better conductivity and will result in a lower resistance.
  • The less water on the surface means poor conductivity and will result in a higher resistance.

The sensor produces an output voltage according to the resistance, which by measuring we can determine whether it’s raining or not.

Specifications

  • This sensor module uses good quality of double-sided material.
  • Anti-conductivity & oxidation with long time use
  • The area of this sensor includes 5cm x 4cm and can be built with a nickel plate on the side
  • The sensitivity can be adjusted by a potentiometer
  • The required voltage is 5V
  • The size of the small PCB is 3.2cm x 1.4cm
  • For easy installation, it uses bolt holes
  • It uses an LM393 comparator with wide voltage
  • The output of the comparator is a clean waveform and driving capacity is above 15mA

Applications

  • This sensor is used as a water preservation device and this is connected to the irrigation system to shut down the system in the event of rainfall.
  • This sensor is used to guard the internal parts of an automobile against the rainfall as well as to support the regular windscreen wiper’s mode.
  • This sensor is used in specialized satellite communications aerials for activating a rain blower over the opening of the aerial feed, to get rid of water droplets from the mylar wrap to keep pressurized as well as dry air within the waveguides.

Example

Automatic Rain Sensing Windshield Wiper

Introduction

  • The RainTracker automotive rain sensor, senses rain or snow hitting the windshield, and automatically runs the wipers at the right speed.
  • we don't have to take our hands off the wheel, or constantly adjust the speed of the wipers as road conditions change.
  • A rain sensor or rain switch is a switching device activated by rainfall
  • In this the sensor projects infrared light into the windshield at a 45-degree angle
  • If the glass is dry, than most of this light is reflected back into the sensor by the front of the windshield.
  • If water droplets are on the glass, than it reflect the light in different direction the wetter the glass, the less light makes it back into the sensor.
  • The electronics and software in the sensor turn on the wipers when the amount of light reflected onto the sensor.
  • Software sets the speed of the wipers based on how fast the moisture builds up between wipes. It can operate the wipers at any speed.

High Level System Diagram

  • In this battery supplies the power to the sensor
  • Then the wiper motor is automatically on during the time of rainfall
  • This sensor is fixed in the vehicle glass
  • It senses the rainfall and giving control signal to the control unit
  • The control unit activate the wiper automatically
  • The rain sensor works on the principle of using water for completing its circuit
  • So when rain falls on it it’s circuit gets completed.

NE555 IC

Circuit diagram

Working

The circuit presented here is not using the optical technology It is built around the famous NE555 timer IC that is working as a monostable multivibrator here. The circuit is using a handmade sensor to detect raindrops. The sensor can be made by attaching 2 wires of 0.5 inch. When two wire in the hand made sensor will detect raindrops then the output of the NE555 IC at the output pin 3 will goes high Activates the relay for a set time period and after that time period is over the relay will switch off again. The activation time period of the relay is few seconds but it can be increased by increasing the value of the capacitor.

  • Detect intensity of rainfall
  • Detect rainfall on windshield
  • Improve safety by decreasing driver distraction
  • Automatically activate windshield wipers once rainfall is detected

Advantage 

  • Sensor cost is low
  • High accuracy
  • Automatic Windshield Wipers
  • Automatic Braking
  • Hands-Free Calling
  • Less power consumption
  • Automotive Safety and Convenience

Disadvantage

  • Additional cost is required in case optical sensor is used
  • This system is applied in the case of water falling on the glass only 

Applications

  • Rain sensing wipers are great convenience feature in a luxury car 
  • More useful in marine applicati ons. 
  • It is use in aircraft
  • Fit in existing housing area


Comments