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/* Connections (UNO): 
 *  HC-SR501 sensor output --------> to pin 8
 *  Voltage output (active_HIGH) --> to pin 5
 *  White_LED cathode -------------> to pin 4
 *  Yellow_LED cathode ------------> to pin 3
*/

void setup() {
  MCUCR |= (1 << PUD); // Disable all pull-ups
  DDRD |= _BV(4) | _BV(5); // White LED | Output signal
  initTIM1();
  initTIM2(); // LED flashes
  sei();
}

void loop() {}

void initTIM1(void) { // Time interval
  TCCR1A = 0x00;
  TCCR1B = 0xCD;
  TIMSK1 = 0x22;
  OCR1A = 15625; // 1 sec at 16MHz
  TCNT1 = OCR1B = 0; 
}

void initTIM2(void) { // Flash LED
  TCCR2A = 0x03;
  TCCR2B = 0x04;
  TIMSK2 = 0;
}

ISR(TIMER1_COMPA_vect) {
  if (++OCR1B == 5) {
    DDRD &= ~_BV(4);
    DDRD |= _BV(3);
    TIMSK2 = 0x06;
  }
  if (OCR1B == 65) {
    TIMSK2 = 0;
    DDRD &= ~_BV(3);
  }
}

ISR(TIMER1_CAPT_vect) {
  (OCR1B > 64) ? (PORTD |= _BV(5)) : (OCR1B = 0);
  TIMSK2 = 0;
  PORTD &= ~_BV(3);
}

ISR(TIMER2_COMPA_vect) {
  --OCR2B;
  PORTD |= _BV(3);
}

ISR(TIMER2_COMPB_vect) {
  PORTD &= ~_BV(3);
}