How to Make an Obstacle Avoiding Robot

        In this post I am going to write the step-by-step procedure to build an obstacle avoiding Robot. I want to keep the cost of this Robot as low as possible so, I am going to use cheap and easily available Sensors like IR LED and Photodiode pair to detect the obstacles instead of expensive sensors like Sharp IR range finder or Ultrasonic transducer. Even though I am using the inexpensive sensors instead of expensive one the performance of the robot is good, you can find how it works from the below You tube vedio –

Materials required: 

      1)      Arduino

      2)      L293D Motor driver IC

      3)      DC Motors (two)

      4)      Wheels (two)

      5)      Castor ball

      6)      IR LED’s (at least 4)

      7)      Photodiodes (at least 2)

       8)     Chassis

       9)   PCB board

     11)   Connecting wires

     12)   9 Volt Batteries (two)

     13)   Double sided tape. 

Step-by-step Procedure To Make an Obstacle Avoiding Robot:

preparing the Sensors:

                      I had said before that, I am going to use IR LED’s and Photodiode as the Sensor to detect the obstacles. If you don’t know How we to use IR LED’s and Photodiode pair to detect the obstacles then, go through my previous post - How to use IR LED andPhotodiode pair with Arduino to detect obstacles.

                     For this project I am going to use the same circuit which I had used in my previous post but, I am going to add one extra IR LED to improve the sensor performance. So, we need two IR LED’s and a Photodiode to prepare one sensor.

                         I had arranged the two IR LED’s and a Photodiode in the PCB board such that the Photodiode is in the middle of two IR LED’s and I had soldered the component (IR LED’s, Photodiode and resistors) which looks like this.

Each sensor has 5 wires two of them are connected to two IR LED’s, one to the Photodiode, one common ground and one wire is to take the readings from the sensor. The circuit diagram of the sensor is shown below. 

L239D Motor driver IC:

            The L239D IC is a motor driver which is used to control two DC motors at a wide range of supply voltages (4.5 volts to 36 volts). Don’t connect the motors directly to Microcontroller the sharp spikes from the motor may damage the Arduino. The L239D IC has 16 legs. The connections of L239D with Arduino and DC Motors are shown in the following picture.

Programming the Arduino:

            The Arduino source code for the Obstacle avoiding robot is presented below -

 int enable=2;         //Enable pins of L239D are connected to Arduino digital pin2  
 int motA1=4;          //pin-2 of L239D is connected to Arduino digital pin4  
 int motA2=5;          //pin-7 of L239D is connected to Arduino digital pin5   
 int motB1=6;          //pin-10 of L239D is connected to Arduino digital pin6  
 int motB2=7;          //pin-15 of L239D is connected to Arduino digital pin7  
 int senA1=8;          //sensorA first IR LED wire is connected to Arduino digital pin8  
 int senA2=9;          //sensorA second IR LED wire is connected to Arduino digital pin9  
 int senA3=10;         //sensorA Photodiode wire is connected to Arduino digital pin10  
 int senB1=11;         //sensorB first IR LED wire is connected to Arduino digital pin11  
 int senB2=12;         //sensorB second IR LED wire is connected to Arduino digital pin12  
 int senB3=13;         //sensorB Photodiode wire is connected to Arduino digital pin13  
 int senAread=0;       //wire connected between photodiode and 3 K resistor of sensorA is connected to Arduino analog pinA0  
 int senBread=1;       //wire connected between photodiode and 3 K resistor of sensorB is connected to Arduino analog pinA1  
 void setup()  
 {  
  pinMode(enable,OUTPUT);  
  digitalWrite(enable,HIGH);  
  pinMode(motA1,OUTPUT);  
  pinMode(motA2,OUTPUT);  
  pinMode(motB1,OUTPUT);  
  pinMode(motB2,OUTPUT);  
  pinMode(senA1,OUTPUT);  
  digitalWrite(senA1,HIGH);  
  pinMode(senA2,OUTPUT);  
  digitalWrite(senA2,HIGH);  
  pinMode(senA3,OUTPUT);  
  digitalWrite(senA3,HIGH);  
  pinMode(senB1,OUTPUT);  
  digitalWrite(senB1,HIGH);  
  pinMode(senB2,OUTPUT);  
  digitalWrite(senB2,HIGH);  
  pinMode(senB3,OUTPUT);  
  digitalWrite(senB3,HIGH);           
  digitalWrite(motA1,HIGH);         //  
  digitalWrite(motA2,LOW);          //In default mode both the motors will rotate forward   
  digitalWrite(motB1,HIGH);         //  
  digitalWrite(motB2,LOW);          //  
 }  
 void loop()  
 {  
  int val1=analogRead(senAread);       // val1 variable stores the readings from sensorA  
  int val2=analogRead(senBread);       // val2 variable stores the readings from sensorB  
  int diff=val1-val2;                  //calculating the difference of val1 and val2  
  if(val1<800 || val2<800)             //if any obstacle is detected by any one of the sensor  
  {  
    if(diff>=0)                        //if obstacle is present at right side of the robot  
    {  
     digitalWrite(motA2,HIGH);       //  
     digitalWrite(motA1,LOW);        //make the bot move backwards  
     digitalWrite(motB2,HIGH);       //  
     digitalWrite(motB1,LOW);        //  
     delay(1000);                    //wait for 1 second  
     digitalWrite(motB2,LOW);        //  
     digitalWrite(motB1,HIGH);       //turn left  
     delay(700);                     //wait for 700 milli seconds   
     digitalWrite(motA1,HIGH);       //  
     digitalWrite(motA2,LOW);        //move forward  
    }   
    else if(diff<0)                 //if obstacle is present at left side of the robot  
    {  
     digitalWrite(motA2,HIGH);       //  
     digitalWrite(motA1,LOW);        //make the bot move backwards  
     digitalWrite(motB2,HIGH);       //  
     digitalWrite(motB1,LOW);        //  
     delay(1000);                    //wait for one second  
     digitalWrite(motA2,LOW);        //  
     digitalWrite(motA1,HIGH);       //turn right  
     delay(700);                     //wait for 700 milli seconds  
     digitalWrite(motB1,HIGH);       //  
     digitalWrite(motB2,LOW);        //move forward  
    }    
  }  
  else                             //if no obstacle is present  
  {  
    digitalWrite(motA1,HIGH);       //  
    digitalWrite(motA2,LOW);        //  
    digitalWrite(motB1,HIGH);       // move forward  
    digitalWrite(motB2,LOW);        //  
  }  
 }  

How program works:

                       The program starts with the initialization of variables. In the “void setup()” method the pin mode is set to output and the pins of sensors are made HIGH i.e., the sensors are at ON condition. Then the motors are made to move forward as a default state. In the “void loop()” method the values from the sensors are stored in variables ‘val1’ and ‘val2’ after that their difference is calculated and stored in the variable ‘diff’ which tells us whether the obstacle is present at the right side or left side (if diff is > 0 the obstacle is present at right side and if diff is < 0 the obstacle is present at the left side of the bot). An if-else ladder is used to make the robot turn according to the obstacle position. If an obstacle is present at the left side of the robot then the bot moves backwards a bit after that turn right side and the moves forwards. If the obstacle is present at right side of the bot then the bot moves backwards a bit after that turns left and then moves forward.

Assembling:

                    Choose any available material for the chassis. I had used an aluminum frame from an old DVD-ROM  for the chassis of the robot. Connect the sensors one at the right-front corner and the other at the left-front corner of the chassis (you can add another sensor at the middle of these two to increase the performance of the robot) by using a double sided tape.

             Attach the castor ball in the middle at the front side of the robot with a double sided tape or any adhesive. Attach the two DC motors in the back left and right positions by using double sided tape or any adhesive. Then the bot will looks like in the below picture.

                   Connect the sensors according to the circuit diagram shown above after that, connect the wires of L239D motor driver according to the pin diagram of L239D IC which is shown above (be careful with the directions of motor otherwise the bot will misbehave). After that Upload the Arduino code into the Arduino Microcontroller. That’s it your bot is ready for the first use.

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