How to Use IR LED and Photodiode with Arduino

      In this post I am going to show you how to use and program IR LED and Photodiode pair with Arduino to detect obstacles in a short range. Before going to do the project let us have a brief look at the IR LED and Photodiode.

IR LED:

                   IR LED means Infrared Light Emitting Diode. The IR LED emits Infrared light which is not visible to human eye. we can find these IR LED's in our TV Remotes. IR LED's works like normal LED's but the material used in the core is different, it emits Infrared Light when current passed through it. These IR LED are used to detect obstacles ahead of the robot. The IR LED emits IR light which gets reflected if any obstacle is present in the direction of emitted IR ray, the reflected IR ray caught by Photodiode which calculates the reflected light strength. The higher the reflected IR
ray strength, the closer is the obstacle and vice-verse

Photodiode:

                  Photodiode is a light sensitive semi-conductor diode which converts the light energy into voltage or current based on the mode of operation. In general Photodiodes are operated in reverse bias condition. The clear Photodiode can detect visible and IR rays to limit the Photodiode to detect only IR rays a black cotting is applied to the glass of the Photodiode. The photodiode allows the current to pass through it if the photodiode is exposed to IR rays and it doesn't allow current to pass through it if no IR rays falls on it. The amount of current passed through the photodiode is directly proportional to amount of IR rays falls on it.

IR LED and Photodiode Project:

                  In this project I am going to show you How to use the IR LED and Photodiode pair to detect the obstacle in-fornt of it. I am going to program the Arduino such that, If an obstacle is present before the IR LED and Photodiode pair with in the threshold range then a buzzer will ring.

Materials required:

1) Arduino                        2) IR LED                      3) Piezo buzzer                         4) some Wires.

Circuit diagram:

How circuit works:

                 In the above circuit the Photodiode is operated in Reverse bias condition i.e., the long leg of photodiode goes to ground and the short leg is connected to 5 Volts supply through 3 K ohms resistor. When the photodiode detects IR rays from the IR LED which is reflected by an obstacle the photodiode conducts then, the current goes to the ground through the photodiode so, the current to the analog pin A0 of Arduino is low so that, we will get low values (around 500) from the analog pin A0 of arduino. In case of no IR rays falls on the photodiode the photodiode doesn't conduct so the current from the digital pin 2 goes to analog pin A0 through the 3 K ohms resister so, the readings from the analog pin A0 of Arduino will be around 900.

Program :

  int pd=2;                      //Photodiode to digital pin 2

 int buzz=13;                   //piezo buzzer to digital pin 13  
 int senRead=0;                 //Readings from sensor to analog pin 0  
 int limit=850;                 //Threshold range of an obstacle  
 void setup()    
 {  
  pinMode(pd,OUTPUT);  
  pinMode(buzz,OUTPUT);  
  digitalWrite(pd,HIGH);       //supply 5 volts to photodiode  
  digitalWrite(buzz,LOW);      //set the buzzer in off mode (initial condition)  
  Serial.begin(9600);          //setting serial monitor at a default baund rate of 9600  
 }  
 void loop()  
 {  
  int val=analogRead(senRead);  //variable to store values from the photodiode  
  Serial.println(val);          // prints the values from the sensor in serial monitor  
  if(val <= limit)              //If obstacle is nearer than the Threshold range  
  {  
   digitalWrite(buzz,HIGH);     // Buzzer will be in ON state  
   delay(20);  
  }  
  else if(val > limit)          //If obstacle is not in Threshold range  
  {  
   digitalWrite(buzz,LOW);      //Buzzer will be in OFF state  
   delay(20);  
  }  
 }  

How program works:

                 The program starts with Initializing variables photodiode 'pd' with digital pin 2, buzzer 'buzz' with digital pin 13, sensor readings 'senRead' to analog pin 0 and the limit variable is set to 500 (reading from the sensor). In the 'void setup()' method the pin mode is definde with the function 'pinMode(variable,OUTPUT/INPUT)'. In the 'void loop()' method the 'val' variable stores the readings from the sensor. The 'Serial.println(val);' method is used to print the values from the sensor to the serial monitor. I had used an if - else ladder to set the buzzer in ON state when the obstacle is in the Threshold range otherwise the Buzzer will be in OFF state.

                If you have any trouble related to this post then, express it in the comment box below.

Related posts :

1) How to make an obstacle avoiding robot

2) How to use and program the Temperature sensor and Photresistor with Arduino.

3) Getting Started with Robotics