//  Khai báo biến
int pulsePin = 0;                 // Dây tín hiệu của Pulse Sensor nối vào chân A0 của Arduino
int blinkPin = 13;                // LED nháy mỗi nhịp tim
int fadePin = 5;                  // LED "fade" mỗi nhịp tim
int fadeRate = 0;                 // sử dụng để "fade" LED với PWM ở chân fadePin



// Biến Volatile sử dụng trong interrupt
volatile int BPM;                   // số nhịp tim mỗi phút
volatile int Signal;                // dữ liệu thô
volatile int IBI = 600;             // thời gian giữa các nhịp
volatile boolean Pulse = false;
volatile boolean QS = false;
volatile int rate[10];                   
volatile unsigned long sampleCounter = 0;       
volatile unsigned long lastBeatTime = 0;      
volatile int P =512;                     
volatile int T = 512;                   
volatile int thresh = 512;              
volatile int amp = 100;                 
volatile bool firstBeat = true;        
volatile boolean secondBeat = true; 


void setup() {
  pinMode(blinkPin, OUTPUT);
  pinMode(fadePin, OUTPUT);
  Serial.begin(115200);        
  interruptSetup();                 // được cài đặt để đọc Sensor mỗi 2mS
}



void loop() {
  sendDataToProcessing('S', Signal);
  if (QS == true) {
    fadeRate = 255;
    sendDataToProcessing('B', BPM);
    sendDataToProcessing('Q', IBI);
    QS = false;
  }
  ledFadeToBeat();
  delay(20);                             // Nghỉ 1 chút
}


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
}

// Đoạn dưới này lười dịch quá :D
void interruptSetup(){     
  // 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      
} 


// THIS IS THE TIMER 2 INTERRUPT SERVICE ROUTINE. 
// Timer 2 makes sure that we take a reading every 2 miliseconds
ISR(TIMER2_COMPA_vect){                         // triggered when Timer2 counts to 124
    cli();                                      // disable interrupts while we do this
    Signal = analogRead(pulsePin);              // read the Pulse Sensor 
    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(firstBeat){                         // if it's the first time we found a beat, if firstBeat == TRUE
             firstBeat = false;                 // clear firstBeat flag
             return;                            // IBI value is unreliable so discard it
            }   
         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;                      
                    }
            }
          
    // 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 = 512;                          // 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 = true;                     // when we get the heartbeat back
     }
  
  sei();                                     // enable interrupts when youre done!
}// end isr