#define SIGNAL_INPUT		2
#define PPL					22000

uint32_t edge_count;

void init_timer(void)
{
	cli();
	
	TCCR1A = 0;// set entire TCCR1A register to 0
	TCCR1B = 0;// same for TCCR1B
	TCNT1  = 0;//initialize counter value to 0
	// set compare match register for 1hz increments
	OCR1A = 15624;// = (16*10^6) / (1*1024) - 1 (must be <65536)
	// turn on CTC mode
	TCCR1B |= (1 << WGM12);
	// Set CS12 and CS10 bits for 1024 prescaler
	TCCR1B |= (1 << CS12) | (1 << CS10);  
	// enable timer compare interrupt
	TIMSK1 |= (1 << OCIE1A);

	sei();
}

void setup()
{
	Serial.begin(38400);
	
	pinMode(SIGNAL_INPUT, INPUT_PULLUP);
	
	pinMode(3, OUTPUT);
	
	attachInterrupt(digitalPinToInterrupt(SIGNAL_INPUT), detectMagnet, FALLING);

	init_timer();
}

void loop()
{
	
}

// Wird bei jeder Flanke aufgerufen, trotz "FALLING"
void detectMagnet()
{
	edge_count++;
}

ISR(TIMER1_COMPA_vect)
{
	uint32_t liter;

	liter = ((edge_count / 2) * 1000) / PPL;

	Serial.print("Durchfluss (Liter): ");
	Serial.print(liter / 1000, DEC);
	Serial.print(".");
	Serial.println(liter % 1000, DEC);
	
	edge_count = 0;
}