Obstacle_avoiding_robot_with_arduino_motor_shield.ino

  #include <AFMotor.h> // library file included 
  
  /**** global declaration ****/
  AF_DCMotor RM(3); // Right dc motor connected to M3 socket
  AF_DCMotor LM(4); // Left dc motor connected to M4 socket
  int trigger = 8; // for US sensor
  int echo = 9; // for US sensor
  float time = 0; // for US sensor
  float distance = 0; // for US sensor
  
  void setup() 
  {
    // set initial speed of motors
    LM.setSpeed(100); // 0 = stop, 255 = max speed
    RM.setSpeed(100); // 0 = stop, 255 = max speed
    
    // set US sensor pins
    pinMode(trigger,OUTPUT);
    pinMode(echo,INPUT);
    delay(7000);
  }
  
  void loop() 
  {
    // generate a random number, either 0 or 1
    int x = random(2);
    
    digitalWrite(trigger,LOW);
    delayMicroseconds(1);
    digitalWrite(trigger,HIGH);
    delayMicroseconds(1);
    digitalWrite(trigger,LOW);
    delayMicroseconds(1);
  
    // echo received
    time = pulseIn(echo,HIGH);
  
    // formula to calculate the distance
    // distance is calculated in cm
    distance = time * 0.034 / 2;   
  
  /***** Control the Trolley *****/
  
  if(distance < 10) // obstacle detected
  {
    // stop 
    LM.run(RELEASE);
    RM.run(RELEASE);
    delay(2000);
  
    // go backward
    LM.setSpeed(200);
    RM.setSpeed(200);
    LM.run(BACKWARD);
    RM.run(BACKWARD);
    delay(900);
      
    // stop
    LM.run(RELEASE);
    RM.run(RELEASE);
    delay(2000);

      // for random turn, either left turn or right turn
      if(x == 0)
      {
        // power right turn
        LM.setSpeed(110);
        RM.setSpeed(110);
        LM.run(FORWARD);
        RM.run(BACKWARD);
        delay(300);
      }
    
      else
      {
        // power left turn
        LM.setSpeed(110);
        RM.setSpeed(110);
        LM.run(BACKWARD);
        RM.run(FORWARD);
        delay(300);
      }
    
    // stop
    LM.run(RELEASE);
    RM.run(RELEASE);
    delay(2000);
  }
  
  else
  {
    // go forward
    LM.setSpeed(100);
    RM.setSpeed(100);
    LM.run(FORWARD);
    RM.run(FORWARD);
  }
  } // loop closed