INFRARED (IR) SENSOR

Infrared (IR) radiation was first discovered by an astronomer named William Herchel in 1800.

When he was measuring the temperature of each color of light (separated by a prism), he noticed that the temperature just beyond the red light was highest .As IR is invisible to the human eye, since its wavelength is longer than that of visible light therefore by observing this phenomenon he discovered infrared light.

Basically, there are two types of infrared (IR) sensors:

·        Active

·        Passive.

 Active Infrared (IR) sensor

It perform both the phenomenon i.e. emitting and detecting infrared radiation. Active IR sensors have two parts:

·        light emitting diode (LED)

·        Receiver

 

An infrared (IR) sensor is an electronic device that measures and detects infrared radiation in its surroundings.

When an object comes close to the sensor, the infrared light from the LED reflects and the object is detected by the receiver. Active IR sensors act as proximity sensor and they are commonly used in obstacle detection systems .For example as in robots.

Passive Infrared (IR) Sensor

Passive infrared (PIR) sensors detect only the infrared radiation and do not emit it from an LED. It is made of:

·        A pyro-electric sensor

·        An infrared filter (which blocks out all other wavelengths of the light)

·        A lens (which collects light into a single point)

 A coating to protect the sensor from other environmental variables, such as humidity, temperature etc.

Generally these sensors are used in motion-based detection. For example as in-home security systems.

THE IR SENSOR CONSIST OF MAIN TWO CONPONENTS:

·        IR TRANSMITTER

·        IR RECEIVER

Infrared (IR) Transmitter

Infrared Transmitter is a light emitting diode (LED) that emits infrared radiations. It is also commonly known as IR LED. Even though an IR LED looks like a normal LED, the radiation emitted by it is invisible to the human eye as the radiations are infrared radiations.

This is the image for an IR LED.

There are different types of infrared transmitters depending upon their wavelengths, output power and response time.

A simple infrared (IR) transmitter can be constructed using:

·       An infrared LED

·        a current limiting resistor and

·       A power supply.

Working for an IR Transmitter

When the transmitter is operated at a supply of 5V, it consumes about 3 to 5 mA of current. Therefore, it can be modulated to produce a particular frequency of infrared light as required.

 

INFRARED (IR) Receiver

Infrared receivers are also called as infrared sensors. They detect the radiation with an IR transmitter. It comes in the form of photo diodes and photo transistors. Infrared photo diodes are different from normal photo diodes because they detect only infrared radiation.

 This is the image for an IR receiver.

It consists of:

·       An IR phototransistor

·        A diode

·        A MOSFET

·       A potentiometer and

·       An LED

 

 

 

Working for an IR receiver

 When the photo transistor receives any infrared radiation, current flows through the circuit and MOSFET turns on. This lights up the LED which acts as a load. Here the potentiometer is used to control the sensitivity of the photo transistor.

OVERALL WORKING

The overall working of an IR sensor is that it works as an Object Detection Sensor. An IR sensor consists of an IR LED and an IR Photo diode; as mentioned above together they are also called as Photo – Coupler or Octo – Coupler.

When the IR transmitter emits radiation, it reaches to the object and some of the radiation reflects back to the IR receiver. Based on the receiving intensity of the IR receiver, the output of the sensor is defined.

CONNECTIONS

The sensor has 3 pins:

·       VCC (connected to +5V of Arduino)

·       GND (connected to GND of Arduino)

·       D0 or OUT(connected to digital output pin of Arduino)

 

 

A simple example for blinking of Arduino led and observing digital output on serial monitor:

const int Sensor=2;

int input = 0;

 

void setup()

{                

  pinMode(13, OUTPUT);          // Pin 13 has an LED connected on most Arduino boards:  

  pinMode(Sensor,INPUT);    //Pin 2 is connected to the output of proximity sensor

  Serial.begin(9600);

}

 

void loop()

{

  if(digitalRead(Sensor)==HIGH)      //Check the sensor output

  {

    digitalWrite(13, HIGH);   // set the LED on

  }

  else

  {

    digitalWrite(13, LOW);    // set the LED off

  }

input = digitalRead(Sensor);

Serial.println(input);

delay(1000);              // wait for one second

}