// Reading liquid flow rate using an Arduino

volatile int NbTopsFan;            //measuring the rising edges of the signal
int Calc;
int hallsensor = 2;                //The pin location of the sensor

void rpm ()                        //This is the function that the interupt calls
{
  NbTopsFan++;                     //This function measures the rising and falling edge of signal
}                                  //The setup() method runs once, when the sketch starts

void setup()
{
 pinMode(hallsensor, INPUT);       //initializes digital pin 2 as an input
 Serial.begin(9600);               //This is the setup function where the serial port is initialised
 attachInterrupt(0, rpm, RISING);  //and the interrupt is attached
}
                                   // the loop() method runs over and over again
                                   // as long as the Arduino has power
void loop ()
{
 NbTopsFan = 0;                    //Set NbTops to 0 ready for calculations
 sei();                            //Enables interrupts
 delay (1000);                     //Wait 1 second
 cli();                            //Disable interrupts
 Calc = (NbTopsFan * 60 / 7.5);    //(Pulse frequency x 60) / 7.5Q = flow rate in L/hour
 Serial.print (Calc, DEC);         //Prints the number calculated above
 Serial.print (" L/hour\r\n");     //Prints "L/hour" and returns a new line
}