Tachometer.pde

//Arduino Code

/*

 * Tachometer

 *

 * M.G.McKinley

 * 6/1/2009

 * Adjust 

 */

//Define Variables

  int ticsPerRev = 16;       // define number of tics per rev of code wheel

  float rpm = 0.0;  // I prefer float for rpm

  volatile int rpmcount =0;  // volitile because the variable is manipulated during the interrupt

  unsigned long timeold = 0; // used to calculate d_t= millis()-timeold;

  int d_t;

  int statusPin = 9;             // LED connected to digital pin (changes state with each tic of code wheel)

volatile byte status= LOW;    // set initial state of status LED

void setup()

 {

   Serial.begin(9600);

   //Interrupt 0 is digital pin 2, so that is where the IR detector is connected

   //Triggers on FALLING (change from HIGH to LOW)

   attachInterrupt(0, rpm_fun, FALLING);

   pinMode(statusPin, OUTPUT); //Use statusPin to flash along with interrupts

 }

 void loop()

 {

   //Update RPM every second

   //Don't process interrupts during calculations

   detachInterrupt(0);

   d_t=millis()-timeold;

   if (d_t >= 1000)

    {

     rpm = float(60.0*1000.0)/float((d_t))*float(rpmcount)/ticsPerRev;

      timeold = millis();

      d_t=0; //reset d_t

      //Serial Port Output

      Serial.print("Time(ms) ");

      Serial.print(timeold); //time at end of interval (hence timeold=millis(); above )

      Serial.print(" TicsPerInterval ");

      Serial.print(rpmcount);

      Serial.print(" RPM ");

      Serial.println(rpm);

      rpmcount = 0; //reset rpmcount

  }

  //Restart the interrupt processing

  attachInterrupt(0, rpm_fun, FALLING);

 }

void rpm_fun()

 {

   //This interrupt is run at each codewheel tic

   detachInterrupt(0); //im not sure if this is necessary here

   rpmcount++; //update rpmcount

   //Toggle status LED  

   if (status == LOW) {

     status = HIGH;

   } else {

     status = LOW;

   }

   digitalWrite(statusPin, status);

   attachInterrupt(0, rpm_fun, FALLING);

 }

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