//code by Crenn from http://thebestcasescenario.com
//project by Charles Gantt from http://themakersworkbench.com


/*To disable interrupts:
 cli();                // disable global interrupts

and to enable them:  
 sei();                // enable interrupts
*/


                                   //Varibles used for calculations
int NbTopsFan; 
int Calc;

                                  //The pin location of the sensor
int hallsensor = 2;

                        
typedef struct{                  //Defines the structure for multiple fans and their dividers
  char fantype;
  unsigned int fandiv;
}fanspec;

//Definitions of the fans
fanspec fanspace[3]={{0,1},{1,2},{2,8}};

char fan = 1;   //This is the varible used to select the fan and it's divider, set 1 for unipole hall effect sensor 
               //and 2 for bipole hall effect sensor 


void rpm ()      //This is the function that the interupt calls 
{ 
 NbTopsFan++; 
} 

              //This is the setup function where the serial port is initialised,
             //and the interrupt is attached
void setup() 
{ 
 pinMode(hallsensor, INPUT); 
 Serial.begin(9600); 
 attachInterrupt(0, rpm, RISING); 
} 
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)/fanspace[fan].fandiv); //Times NbTopsFan (which is apprioxiamately the fequency the fan is spinning at) by 60 seconds before dividing by the fan's divider
   Serial.print (Calc, DEC); //Prints the number calculated above
   Serial.print (" rpm\r\n"); //Prints " rpm" and a new line
}