Arduino code for obstacle avoiding robot using ultrasonic sensor

//connect trig pin of ultrasonic sensor to port 5

const int trig = 5;

 //connect echo pin of ultrasonic sensor to port 7

const int echo = 7;

 //giving motor connections as follows

const int m1a = 8;

const int m1b = 9;

const int m2a = 12;

const int m2b = 13;

void setup() 

{

  // activate serial monitor

 Serial.begin(9600);

 // defining trig pin as output since it produces sound waves

 pinMode(trig, OUTPUT);

 // defining echo pin as input since it receives sound waves

 pinMode(echo, INPUT);

 // defining motor pins as outputs

 pinMode(m1a, OUTPUT);

 pinMode(m1b, OUTPUT);

 pinMode(m2a, OUTPUT);

 pinMode(m2b, OUTPUT);

}

void loop() 

{

  // define two variables to store time and distance

 long duration, distance;

 // code for producing sound waves from transmitter part of sensor

 digitalWrite(trig, LOW);

 delayMicroseconds(2);

 digitalWrite(trig, HIGH);

 delayMicroseconds(10);

 digitalWrite(trig, LOW);

 // finding time using pulseIn function and assign it into the variable duration

 duration = pulseIn(echo, HIGH); // in microsecond

 // calculating distance by multiplying time and velocity (0.034 cm per microsecond)

 // it is then divided by 2 since the wave has traveled twice the distance between the sensor and the obstacle 

 distance = duration * 0.034/2; //in cm

// print distance on serial monitor 

Serial.println(distance);

// checking whether the distance is less than 20 cm (may be varied)

 if (distance < 20)

    {

      // give command to take turn (left or right). Below code may vary according to the connection

      digitalWrite(m1a, HIGH);

      digitalWrite(m1b, LOW);

      digitalWrite(m2a, LOW);

      digitalWrite(m2b, HIGH);

    }

// checking whether the distance is greater than or equal to 20 cm   

else if (distance >= 20)

   {

      // give command to go straight. Below code may vary according to the connection

      digitalWrite(m1a, HIGH);

      digitalWrite(m1b, LOW);

      digitalWrite(m2a, HIGH);

      digitalWrite(m2b, LOW);

   }

// giving a delay of one second   

delay(1000);

}
// recommended to visit Arduino website and Instructables website