Arduino v1

//  VARIABLES
int pulsePin = 0;                 // Pulse Sensor purple wire connected to analog pin 0
int blinkPin = 13;                // pin to blink led at each beat
int fadePin = 6;                  // pin to do fancy classy fading blink at each beat
int fadeRate = 10;                 // used to fade LED on with PWM on fadePin
int alarmPin = 11;

// these variables are volatile because they are used during the interrupt service routine!
volatile int BPM;                   // used to hold the pulse rate
volatile int Signal;                // holds the incoming raw data
volatile int IBI = 600;             // holds the time between beats, the Inter-Beat Interval
volatile boolean Pulse = false;     // true when pulse wave is high, false when it's low
volatile boolean QS = false;        // becomes true when Arduoino finds a beat.

boolean alarm = false;
int bpmCount = 0;
int limit = 80;

int sample[10];
int numSamples = 9; //10st

double firstAverage = 0;
double secondAverage = 0;

boolean tripped = false;

void setup()
{
  pinMode(blinkPin, OUTPUT);         // pin that will blink to your heartbeat!
  pinMode(fadePin, OUTPUT);          // pin that will fade to your heartbeat!
  pinMode(alarmPin, OUTPUT);
  Serial.begin(115200);             // we agree to talk fast!
  interruptSetup();                 // sets up to read Pulse Sensor signal every 2mS
   // UN-COMMENT THE NEXT LINE IF YOU ARE POWERING The Pulse Sensor AT LOW VOLTAGE,
   // AND APPLY THAT VOLTAGE TO THE A-REF PIN
   //analogReference(EXTERNAL);
}

void loop()
{
  sendDataToProcessing('S', Signal); // send Processing the raw Pulse Sensor data
  if (QS == true)                    // Quantified Self flag is true when arduino finds a heartbeat
  {
    fadeRate = 255;                  // Set 'fadeRate' Variable to 255 to fade LED with pulse
    sendDataToProcessing('B',BPM);   // send heart rate with a 'B' prefix
    sendDataToProcessing('Q',IBI);   // send time between beats with a 'Q' prefix
    QS = false;                      // reset the Quantified Self flag for next time

    sample[bpmCount] = BPM;

    bpmCount += 1;

    if(bpmCount == numSamples)
    {
        firstAverage = getAverageBpm();
        tripped = true;
        bpmCount = 0;
    }

    if(tripped)
    {
        secondAverage = getAverageBpm();

        if(firstAverage - secondAverage > 10)
        {
            alarm = true;
        }
        else
        {
            alarm = false;
        }

        tripped = false;
    }

    Serial.print("count: ");
    Serial.println(bpmCount);
  }

  if(alarm)
  {
    analogWrite(alarmPin, 255); //Sätt igång alarmet
  }
  else
  {
    analogWrite(alarmPin, 0); //Stäng av alarmet
  }

  ledFadeToBeat(); //Fada led:en på lådan

  delay(20);
}

void ledFadeToBeat()
{
    fadeRate -= 15;                         //  set LED fade value
    fadeRate = constrain(fadeRate,0,255);   //  keep LED fade value from going into negative numbers!
    analogWrite(fadePin,fadeRate);          //  fade LED
}

void sendDataToProcessing(char symbol, int data)
{
    Serial.print(symbol);                // symbol prefix tells Processing what type of data is coming
    Serial.println(data);                // the data to send culminating in a carriage return
}

double getAverageBpm()
{
    int sum = 0;
    for(int i = 0; i < 10; i++)
    {
        sum += sample[i];
    }

    return (double)sum / numSamples+1;
}