misurare RPM ventola pc arduino display

#include <LiquidCrystal.h>
#define Backlight 10
LiquidCrystal lcd(8, 9, 4, 5, 6, 7);
int  Calc;
int NbTopsFan;
int hallsensor = 2;
typedef struct{
  char fantype;
  unsigned int fandiv;
}fanspec;

fanspec fanspace[3]={{0,1},{1,2},{2,8}};

char fan = 1;

void rpm ()
{
 NbTopsFan++;
}

void setup()
{
 lcd.begin(16, 2);
 pinMode(Backlight, OUTPUT);
 digitalWrite(Backlight, HIGH);
 pinMode(hallsensor, INPUT);
 attachInterrupt(0, rpm, RISING);
}

void loop ()
{
   NbTopsFan = 0;
   sei(); //Abilita interrupts
   delay (1000);
   cli(); //Disabilita interrupts
   Calc = ((NbTopsFan * 60)/fanspace[fan].fandiv);
   lcd.setCursor(0,0); // Colonna 0, Riga 0
   lcd.print("Bettonte  ");
   lcd.setCursor (0,1); //Colonna 0, Riga 1
   lcd.print ("RPM: ");
   lcd.print (Calc);
   lcd.print ("    ");
}