Obstacle Avoiding Robot with L293D

Projects Discussion and Showcase Robotics
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AWOL:
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I want to write a code with Ardiuno Uno.I had changed the code which i wrote before.There is a problem.The problem is that if robot's motor catch a obstacle,motors always will run because sensor is not see the any obstacles which is behind the sensor.But i did not want this.I want to all motors stop and run backward until 1 second.What do i do?

Now,i have tried to work following code:

#include <AFMotor.h>
#include <Servo.h>
#include <NewPing.h>
#define TRIG_PIN A4 
#define ECHO_PIN A5 
#define MAX_SPEED 180  
#define COLL_DIST 40 
#define TURN_DIST COLL_DIST +20 
NewPing sonar(TRIG_PIN, ECHO_PIN); 

AF_DCMotor motor1(1, MOTOR12_1KHZ); 
AF_DCMotor motor2(4, MOTOR12_1KHZ); 
Servo servo; 
const int led = 15;
int leftDistance, rightDistance;
int curDist;
int speedSet = 0;


void setup() {
 Serial.begin(9600);
 pinMode(led,OUTPUT);
 servo.attach(9);  
 servo.write(90);
 delay(500); 

}

void loop() {
 Serial.println(readPing());
 digitalWrite(led,HIGH);
 Serial.println("START FORWARD");
 accelerateForward();
 if (readPing()<COLL_DIST){
   Serial.println("Collision Detected");
   moveStop();
   changePath();
   compareDistance();
   accelerateForward();
 }



}


void changePath() { 
 servo.write(20);  
 delay(600);
 rightDistance = readPing(); 
 delay(600);
 servo.write(90); 
 delay(600);
 servo.write(160);  
 delay(600);
 leftDistance = readPing();
 delay(600);
 servo.write(90);
 delay(600);
}


void compareDistance()  
{
 if (leftDistance>rightDistance) 
 {
   turnLeft();
 }
 else if (rightDistance>leftDistance)
 {
   turnRight();
 }
 else 
 {
   turnAround();
 }
}



int readPing() {
 delay(70);  
 unsigned int uS = sonar.ping();
 int cm = uS/US_ROUNDTRIP_CM;
 Serial.print(cm);
 Serial.println(" cm");
 return cm;
}

void moveStop() {
 Serial.println("Stopped");
 motor1.run(RELEASE); 
 motor2.run(RELEASE);
 delay(800);
}  

void accelerateForward() {
 Serial.println("Start Forward");
 motor1.run(FORWARD);     
 motor2.run(FORWARD);    
 for (speedSet = 0; speedSet < MAX_SPEED; speedSet +=2)
 {
   motor1.setSpeed(speedSet);
   motor2.setSpeed(speedSet);
 }
}


void turnRight() {
 Serial.println("Turn Right");
 motor1.run(FORWARD);     
 motor2.run(BACKWARD);  
 delay(500);      
} 

void turnLeft() {
 Serial.println("Turn Left");
 motor1.run(BACKWARD);     
 motor2.run(FORWARD);     
 delay(500);
} 

void turnAround() {
 Serial.println("Turn Around");
 motor1.run(FORWARD);      
 motor2.run(BACKWARD);     
 delay(1000);
}