#define TriggerPIN  3 //D03 (Uno, Nano, Mini)
#define StatusLED  13 //D13

// to find the perfect timing window set FLASH_TIMER_DURATION=2 and then change the FLASH_TIMER_DELAY up and down to find the limits (point the camera on the Status LED and watch the brightness change)
// 502 off
// 503 weak
// 504 better
// 505 full
// .
// .
// .
// 518 full
// 519 better
// 520 weak
// 521 off
`
#define FLASH_TIMER_DELAY    505  // (16 MHz / 1024) * 0.032384 - 1 ≈ 505 für 32,384ms Interrupt
#define FLASH_TIMER_DURATION  15  // (16 MHz / 1024) * 0.001024 - 1 ≈  15 für  1,024ms Interrupt

unsigned long starttime, endtime, duration, pause;
unsigned int triggered=0, status=0, i=0, FLASH_ON=0;

void setup() {
  pinMode(StatusLED,OUTPUT);                // set PIN to OUTPUT
  digitalWrite(StatusLED,LOW);              // set PIN to LOW (StatusLED OFF)
  
  pinMode(TriggerPIN,INPUT_PULLUP);         // set PIN to INPUT
    
  attachInterrupt(digitalPinToInterrupt(TriggerPIN),TriggerISR,CHANGE);   // SET InterruptPIN, ISR and Mode

  // Timer
  TCCR1A = 0;
  TCCR1B = (1 << WGM12) | (1 << CS12) | (1 << CS10);  // CTC Modus, Prescaler 1024
  OCR1A = FLASH_TIMER_DELAY;
  TIMSK1 = (1 << OCIE1A);  // Timer1 Compare Match Interrupt aktivieren

  interrupts();                             // enable Interrupts

  Serial.begin(115200);                     // initialize serial
}


void loop() {
  if (triggered==0) {
    TCNT1 = 0;  // Timer reset
  }

  if (status==1) {    
    status=0;
    Serial.println(i);
    Serial.print("pause:");
    Serial.print(pause/1000);
    Serial.println("ms");
    Serial.print("duration:");
    Serial.print(duration);
    Serial.println("us");
    Serial.println("-------------------------");
    i++;
  }
}


void TriggerISR() {                       // ISR function excutes when PIN is triggered
  if (digitalRead(TriggerPIN)==HIGH) {    // check if PIN is high or low and set Flash PIN
    if (triggered==0) {
      triggered=1;
      TCNT1 = 0;  // Timer reset
    }
    starttime = micros();
    pause=(starttime-endtime);
  }
  else {
    endtime = micros();
    duration=endtime-starttime;
    status=1;                             // allow posting new Timings
  }
}


ISR(TIMER1_COMPA_vect) {                  // Timer
  if (FLASH_ON==0) {
    digitalWrite(StatusLED,HIGH);
    TCNT1 = FLASH_TIMER_DELAY - FLASH_TIMER_DURATION;  // Timer reset to 1ms
    FLASH_ON=1;
  }
  else {
    digitalWrite(StatusLED,LOW);
    FLASH_ON=0;
    triggered=0;
  }
}