int capture;

#define BTN_PIN 2
void setup() {
  // put your setup code here, to run once:

  TIMSK1 |= (1<<ICIE1);

  TCCR1A &= (~(1<<WGM10)) & (~(1<<WGM11));
  TCCR1B &= (~(1<<WGM12)) & (~(1<<WGM13));

  TCCR1B |= (1<<CS12) | (1<<CS10);
  TCCR1B &= (~(1<<CS11));

  TCNT1=0;

  TCCR1B|=(0<<ICES1); //FALLING EDGE TRIGGER INTERRUPT;


  pinMode(BTN_PIN, INPUT_PULLUP);

  
Serial.begin(9600);
                   Serial.println("capture");
                   Serial.print('\n');
}

void loop() {

}

ISR(TIMER1_CAPT_vect)   // this isr routine stats with falling edge interrupt
  {
   
     capture = ICR1;                 
   

                   Serial.println(capture);
                   Serial.print('\n');

                   }