Interrupt.ino

volatile int rate[10];                    // array to hold last ten IBI values
volatile unsigned long sampleCounter = 0;          // used to determine pulse timing
volatile unsigned long lastBeatTime = 0;           // used to find IBI
volatile int P = 512;                     // used to find peak in pulse wave, seeded
volatile int T = 512;                     // used to find trough in pulse wave, seeded
volatile int thresh = 530;                // used to find instant moment of heart beat, seeded
volatile int amp = 0;                   // used to hold amplitude of pulse waveform, seeded
volatile boolean firstBeat = true;        // used to seed rate array so we startup with reasonable BPM
volatile boolean secondBeat = false;      // used to seed rate array so we startup with reasonable BPM


hw_timer_t * timer = NULL;
volatile SemaphoreHandle_t timerSemaphore;
portMUX_TYPE timerMux = portMUX_INITIALIZER_UNLOCKED;


#define ESP32  // timer interrupt code for ESP32 added by coniferconifer
// see https://github.com/espressif/arduino-esp32/blob/master/libraries/ESP32/examples/Timer/RepeatTimer/RepeatTimer.ino
//
#ifdef ESP32
void IRAM_ATTR onTimer() {
#else
// THIS IS THE TIMER 2 INTERRUPT SERVICE ROUTINE.
// Timer 2 makes sure that we take a reading every 2 miliseconds
ISR(TIMER2_COMPA_vect) {
#endif

#ifdef ESP32
  portENTER_CRITICAL_ISR(&timerMux);          // cli();
#else
  cli();                                      // disable interrupts while we do this
#endif

  // triggered when Timer2 counts to 124
#ifndef ESP32
  Signal = analogRead(pulsePin);              // read the Pulse Sensor
#else
  Signal = analogRead(pulsePin) / 4;            // read the Pulse Sensor, bits of ESP32 ADC ch is 4 times larger
#endif
  sampleCounter += 2;                         // keep track of the time in mS with this variable
  int N = sampleCounter - lastBeatTime;       // monitor the time since the last beat to avoid noise

  //  find the peak and trough of the pulse wave
  if (Signal < thresh && N > (IBI / 5) * 3) { // avoid dichrotic noise by waiting 3/5 of last IBI
    if (Signal < T) {                       // T is the trough
      T = Signal;                         // keep track of lowest point in pulse wave
    }
  }

  if (Signal > thresh && Signal > P) {        // thresh condition helps avoid noise
    P = Signal;                             // P is the peak
  }                                        // keep track of highest point in pulse wave

  //  NOW IT'S TIME TO LOOK FOR THE HEART BEAT
  // signal surges up in value every time there is a pulse
  if (N > 250) {                                  // avoid high frequency noise
    if ( (Signal > thresh) && (Pulse == false) && (N > (IBI / 5) * 3) ) {
      Pulse = true;                               // set the Pulse flag when we think there is a pulse
      digitalWrite(blinkPin, HIGH);               // turn on pin 13 LED
      IBI = sampleCounter - lastBeatTime;         // measure time between beats in mS
      lastBeatTime = sampleCounter;               // keep track of time for next pulse

      if (secondBeat) {                      // if this is the second beat, if secondBeat == TRUE
        secondBeat = false;                  // clear secondBeat flag
        for (int i = 0; i <= 9; i++) {       // seed the running total to get a realisitic BPM at startup
          rate[i] = IBI;
        }
      }

      if (firstBeat) {                       // if it's the first time we found a beat, if firstBeat == TRUE
        firstBeat = false;                   // clear firstBeat flag
        secondBeat = true;                   // set the second beat flag
        sei();                               // enable interrupts again
        return;                              // IBI value is unreliable so discard it
      }


      // keep a running total of the last 10 IBI values
      word runningTotal = 0;                  // clear the runningTotal variable

      for (int i = 0; i <= 8; i++) {          // shift data in the rate array
        rate[i] = rate[i + 1];                // and drop the oldest IBI value
        runningTotal += rate[i];              // add up the 9 oldest IBI values
      }

      rate[9] = IBI;                          // add the latest IBI to the rate array
      runningTotal += rate[9];                // add the latest IBI to runningTotal
      runningTotal /= 10;                     // average the last 10 IBI values
      BPM = 60000 / runningTotal;             // how many beats can fit into a minute? that's BPM!
      QS = true;                              // set Quantified Self flag
      // QS FLAG IS NOT CLEARED INSIDE THIS ISR
    }
  }

  if (Signal < thresh && Pulse == true) {  // when the values are going down, the beat is over
    digitalWrite(blinkPin, LOW);           // turn off pin 13 LED
    Pulse = false;                         // reset the Pulse flag so we can do it again
    amp = P - T;                           // get amplitude of the pulse wave
    thresh = amp / 2 + T;                  // set thresh at 50% of the amplitude
    P = thresh;                            // reset these for next time
    T = thresh;
  }

  if (N > 2500) {                          // if 2.5 seconds go by without a beat
    thresh = 530;                          // set thresh default
    P = 512;                               // set P default
    T = 512;                               // set T default
    lastBeatTime = sampleCounter;          // bring the lastBeatTime up to date
    firstBeat = true;                      // set these to avoid noise
    secondBeat = false;                    // when we get the heartbeat back
  }

#ifndef ESP32
  sei();                                   // enable interrupts when youre done!
#else
  portEXIT_CRITICAL_ISR(&timerMux);
  // Give a semaphore that we can check in the loop
  xSemaphoreGiveFromISR(timerSemaphore, NULL);
  // It is safe to use digitalRead/Write here if you want to toggle an output
#endif
}// end isr

void interruptSetup() { // CHECK OUT THE Timer_Interrupt_Notes TAB FOR MORE ON INTERRUPTS
#ifndef ESP32
  // Initializes Timer2 to throw an interrupt every 2mS.
  TCCR2A = 0x02;     // DISABLE PWM ON DIGITAL PINS 3 AND 11, AND GO INTO CTC MODE
  TCCR2B = 0x06;     // DON'T FORCE COMPARE, 256 PRESCALER
  OCR2A = 0X7C;      // SET THE TOP OF THE COUNT TO 124 FOR 500Hz SAMPLE RATE
  TIMSK2 = 0x02;     // ENABLE INTERRUPT ON MATCH BETWEEN TIMER2 AND OCR2A
  sei();             // MAKE SURE GLOBAL INTERRUPTS ARE ENABLED
  // Create semaphore to inform us when the timer has fired
#else
  timerSemaphore = xSemaphoreCreateBinary();

  // Use 1st timer of 4 (counted from zero).
  // Set 80 divider for prescaler (see ESP32 Technical Reference Manual for more
  // info).
  timer = timerBegin(0, 80, true);

  // Attach onTimer function to our timer.
  timerAttachInterrupt(timer, &onTimer, true);

  // Set alarm to call onTimer function every second (value in microseconds).
  // Repeat the alarm (third parameter)
  timerAlarmWrite(timer, 2000, true);

  // Start an alarm
  timerAlarmEnable(timer);
#endif
}