Thanks... 
Then this will be my first step...if I "aktivate" Interrupt 1 on pin 3
This will give me the opportunity to read a sensor at pin 3 ??
#include <Wire.h>
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27,16,2);
// set the LCD address to 0x27 for a 20 chars and 2 line display
byte sensorInterrupt = 0;// 0 = pin 2; 1 = pin 3
byte sensorInterrupt = 1;// 0 = pin 2; 1 = pin 3
byte sensorPin = 2;
byte sensorPin = 3;
// The hall-effect flow sensor outputs approximately 4.5 pulses per second per
// litre/minute of flow.
float calibrationFactor = 50;
volatile byte pulseCount;
float flowRate;
unsigned int flowMilliLitres;
unsigned long oldTime;
