ISR_RPM_Measure.ino

/****************************************************************************************************************************
  ISR_RPM_Measure.ino
  For Arduino and Adadruit AVR 328(P) and 32u4 boards
  Written by Khoi Hoang

  Built by Khoi Hoang https://github.com/khoih-prog/TimerInterrupt
  Licensed under MIT license

  Now we can use these new 16 ISR-based timers, while consuming only 1 hardware Timer.
  Their independently-selected, maximum interval is practically unlimited (limited only by unsigned long miliseconds)
  The accuracy is nearly perfect compared to software timers. The most important feature is they're ISR-based timers
  Therefore, their executions are not blocked by bad-behaving functions / tasks.
  This important feature is absolutely necessary for mission-critical tasks.

  Notes:
  Special design is necessary to share data between interrupt code and the rest of your program.
  Variables usually need to be "volatile" types. Volatile tells the compiler to avoid optimizations that assume
  variable can not spontaneously change. Because your function may change variables while your program is using them,
  the compiler needs this hint. But volatile alone is often not enough.
  When accessing shared variables, usually interrupts must be disabled. Even with volatile,
  if the interrupt changes a multi-byte variable between a sequence of instructions, it can be read incorrectly.
  If your data is multiple variables, such as an array and a count, usually interrupts need to be disabled
  or the entire sequence of your code which accesses the data.
 *****************************************************************************************************************************/
/* RPM Measuring uses high frequency hardware timer 1Hz == 1ms) to measure the time from of one rotation, in ms
   then convert to RPM. One rotation is detected by reading the state of a magnetic REED SW or IR LED Sensor
   Asssuming LOW is active.
   For example: Max speed is 600RPM => 10 RPS => minimum 100ms a rotation. We'll use 80ms for debouncing
   If the time between active state is less than 8ms => consider noise.
   RPM = 60000 / (rotation time in ms)

   We use interrupt to detect whenever the SW is active, set a flag
   then use timer to count the time between active state
*/

// These define's must be placed at the beginning before #include "TimerInterrupt.h"
// _TIMERINTERRUPT_LOGLEVEL_ from 0 to 4
// Don't define _TIMERINTERRUPT_LOGLEVEL_ > 0. Only for special ISR debugging only. Can hang the system.
#define TIMER_INTERRUPT_DEBUG         0
#define _TIMERINTERRUPT_LOGLEVEL_     0

#if ( defined(__AVR_ATmega644__) || defined(__AVR_ATmega644A__) || defined(__AVR_ATmega644P__) || defined(__AVR_ATmega644PA__)  || \
        defined(ARDUINO_AVR_UNO) || defined(ARDUINO_AVR_NANO) || defined(ARDUINO_AVR_MINI) ||    defined(ARDUINO_AVR_ETHERNET) || \
        defined(ARDUINO_AVR_FIO) || defined(ARDUINO_AVR_BT)   || defined(ARDUINO_AVR_LILYPAD) || defined(ARDUINO_AVR_PRO)      || \
        defined(ARDUINO_AVR_NG) || defined(ARDUINO_AVR_UNO_WIFI_DEV_ED) || defined(ARDUINO_AVR_DUEMILANOVE) || defined(ARDUINO_AVR_FEATHER328P) || \
        defined(ARDUINO_AVR_METRO) || defined(ARDUINO_AVR_PROTRINKET5) || defined(ARDUINO_AVR_PROTRINKET3) || defined(ARDUINO_AVR_PROTRINKET5FTDI) || \
        defined(ARDUINO_AVR_PROTRINKET3FTDI) )
  #define USE_TIMER_1     true
  #warning Using Timer1
#else          
  #define USE_TIMER_3     true
  #warning Using Timer3
#endif

#include "TimerInterrupt_Generic.h"

#if !defined(LED_BUILTIN)
  #define LED_BUILTIN     13
#endif

unsigned int interruptPin = 2;

#define TIMER_INTERVAL_MS        1
#define DEBOUNCING_INTERVAL_MS    80

#define LOCAL_DEBUG      1

volatile unsigned long rotationTime = 0;
float RPM       = 0.00;
float avgRPM    = 0.00;

volatile int debounceCounter;

#define KAVG      100

volatile bool activeState = false;

void detectRotation(void)
{
  activeState = true;
}

void TimerHandler()
{
  if ( activeState )
  {
    // Reset to prepare for next round of interrupt
    activeState = false;

    if (debounceCounter >= DEBOUNCING_INTERVAL_MS / TIMER_INTERVAL_MS )
    {

      //min time between pulses has passed
      RPM = (float) ( 60000.0f / ( rotationTime * TIMER_INTERVAL_MS ) );

      avgRPM = ( 2 * avgRPM + RPM) / 3,

#if (TIMER_INTERRUPT_DEBUG > 1)
      Serial.print("RPM = "); Serial.print(avgRPM);
      Serial.print(", rotationTime ms = "); Serial.println(rotationTime * TIMER_INTERVAL_MS);
#endif

      rotationTime = 0;
      debounceCounter = 0;
    }
    else
      debounceCounter++;
  }
  else
  {
    debounceCounter++;
  }

  if (rotationTime >= 5000)
  {
    // If idle, set RPM to 0, don't increase rotationTime
    RPM = 0;

#if (TIMER_INTERRUPT_DEBUG > 1)
    Serial.print("RPM = "); Serial.print(RPM); Serial.print(", rotationTime = "); Serial.println(rotationTime);
#endif

    rotationTime = 0;
  }
  else
  {
    rotationTime++;
  }
}


void setup()
{
  Serial.begin(115200);
  while (!Serial);

  Serial.print(F("\nStarting ISR_RPM_Measure on ")); Serial.println(BOARD_TYPE);
  Serial.println(TIMER_INTERRUPT_VERSION);
  Serial.println(TIMER_INTERRUPT_GENERIC_VERSION);
  Serial.print(F("CPU Frequency = ")); Serial.print(F_CPU / 1000000); Serial.println(F(" MHz"));

  pinMode(LED_BUILTIN, OUTPUT);
  pinMode(interruptPin, INPUT_PULLUP);

  // Timer0 is used for micros(), millis(), delay(), etc and can't be used
  // Select Timer 1-2 for UNO, 1-5 for MEGA, 1,3,4 for 16u4/32u4
  // Timer 2 is 8-bit timer, only for higher frequency
  // Timer 4 of 16u4 and 32u4 is 8/10-bit timer, only for higher frequency
  
#if USE_TIMER_1

  ITimer1.init();

  // Using ATmega328 used in UNO => 16MHz CPU clock ,

  if (ITimer1.attachInterruptInterval(TIMER_INTERVAL_MS, TimerHandler))
  {
    Serial.print(F("Starting  ITimer1 OK, millis() = ")); Serial.println(millis());
  }
  else
    Serial.println(F("Can't set ITimer1. Select another freq. or timer"));
    
#elif USE_TIMER_3

  ITimer3.init();

  if (ITimer3.attachInterruptInterval(TIMER_INTERVAL_MS, TimerHandler))
  {
    Serial.print(F("Starting  ITimer3 OK, millis() = ")); Serial.println(millis());
  }
  else
    Serial.println(F("Can't set ITimer3. Select another freq. or timer"));

#endif

  // Assumming the interruptPin will go LOW
  attachInterrupt(digitalPinToInterrupt(interruptPin), detectRotation, FALLING);
}

void loop()
{

}