// DC motor and ultrasonic sensor, spins when nothing is detected and stops when an object is detected
 #include "SR04.h"
 #define TRIG_PIN 12
 #define ECHO_PIN 11
 SR04 sr04 = SR04(ECHO_PIN,TRIG_PIN);
 long a;
 bool detectObject=false;

 void setup(){
   TCCR1A = 0;           // Init Timer1
   TCCR1B = 0;           // Init Timer1
   TCCR1B |= B00000011;  // Prescalar = 64
   TCNT1 = 40535;        // Timer Preloading to make 25000 ticks count which is 100 ms
   TIMSK1 |= B00000001;  // Enable Timer Overflow Interrupt
 }

 void loop(){
   if (detectObject == false){
     analogWrite(3, 255); // Write PWM to pin 3
   }
   else
     analogWrite(3, 0);
 }

 ISR(TIMER1_OVF_vect)
 {
   a=sr04.Distance();
   if(a<25){
     detectObject = true;
   }
   else detectObject = false;
   TCNT1 = 40535; // Timer Preloading
 }