Heart Rate Monitor

Forum 2005-2010 (read only) General Exhibition
2

First, I am receiving the signal from a Polar chest belt with the Rick Moll's circuit (http://rick.mollprojects.com/hrm/)

** I will soon replace it with the Polar Heart Rate module from Sparkfun: http://www.sparkfun.com/commerce/product_info.php?products_id=8660.

I put the signal on Port 2 of Arduino to use an interrupt in my code (which is at the bottom of this topic).

I, then, use port 3 to port 6 to send the BCD code to the the 7 segments and port 7 and 8 to choose which segment I use.
Here is my first version of the schematic:

Here is my code, I would like to know a better way to calculate the heart rate. Now I am doing an average of some value than i do it again and again. The beat per minute showing on my watch is varying slower than what I have on the 7-segments and changes in the beat per minute are less important. How could I improve this? Thank you for your help.

volatile int moyennefrequence, D3 = 3, D4 = 4, D5 =5, D6 = 6, D7 = 7, D8 = 8;
volatile int state = 0, lastTime, thisTime; 

void setup()
{
  pinMode(D3, OUTPUT);                                   //P3 to P8 as output
  pinMode(D4, OUTPUT);
  pinMode(D5, OUTPUT);
  pinMode(D6, OUTPUT);
  pinMode(D7, OUTPUT);
  pinMode(D8, OUTPUT);
  attachInterrupt(0, pulse, CHANGE);                     //call pulse function when an interrupt is detected on Port 2;  
}

void loop()
{
  static int i = 0, m, fc[5], waitTime, sommefrequence = 0, frequence;
  long DEAD_TIME     = 2000;
  
  if (state == 2) {                                    //if 2nd pulse detected
    frequence = (60000 / (thisTime-lastTime));         //calculate bpm using time between the two pulses
      if ((frequence >= 40) && (frequence <= 220)) {   //if bpm is between 40 and 220
        fc[i] = frequence;                             //add bpm at the position "i" in the array
        i++;                                           //change array position
    }
    }
   
  waitTime = millis()-lastTime;                        //Time since no pulses were detected
  if (waitTime > DEAD_TIME) {                          //if too long
    moyennefrequence = 0;                              //bpm = 0;
  }
  if (i == 4) {                                        //if array is full
    for(m = 0; m < 5; m++) {
    sommefrequence = fc[m] + sommefrequence;           //addition of the bpm in the array
    }
  moyennefrequence = (sommefrequence / 4);             //calculate average
  i = 0;                                               //reset array position
  sommefrequence = 0;                                  //reset addition result
 }
  ssegments();                                         //call ssegments function                                  
}

void pulse()
{
  if (state == 2) {                                   //if second pulse is detected
    lastTime = thisTime;                              //the time of the first pulse is put in the lastTime variable
    state = 1;                                        //reset pulse counter at 1
  }
  if (state < 2) {                                    //if less than 2 pulse has been detected
    thisTime = millis();                              //put the current time in thisTime variable
    state = state++;                                  //increment pulse counter
  }
}


void ssegments() {  
  int unite, dizaine, centaine;
  unite = (moyennefrequence % 10);                  //put the first number of the decimal value of bpm in unite variable
  dizaine = (((moyennefrequence % 100) - unite)/10);//put the second number of the decimal value of bpm in dizaine variable 
  centaine = (((moyennefrequence % 1000) - dizaine - unite)/100);//put the third number of the decimal value of bpm in centaine variable
  
  
  digitalWrite(D7, LOW);  //address of first number
  digitalWrite(D8, HIGH);
  chiffre(unite);         //send unite to funtion chiffre to be displayed
  delay(1);
  digitalWrite(D7, HIGH);//address of second number
  digitalWrite(D8, LOW);
  chiffre(dizaine);      //send dizaine to funtion chiffre to be displayed
  delay(1);
  digitalWrite(D7, HIGH);//address of third number
  digitalWrite(D8, HIGH);
  chiffre(centaine);     //send centaine to funtion chiffre to be displayed
  delay(1);
  
}

void chiffre(int i) {  //send bcd value of decimal number to ports D3 to D6
  switch(i){
    case 1:
      digitalWrite(D6, HIGH);
      digitalWrite(D3, LOW);
      digitalWrite(D4, LOW);
      digitalWrite(D5, LOW);
      break;
    case 2:
      digitalWrite(D6, LOW);
      digitalWrite(D3, HIGH);
      digitalWrite(D4, LOW);
      digitalWrite(D5, LOW);
      break;
    case 3:
      digitalWrite(D6, HIGH);
      digitalWrite(D3, HIGH);
      digitalWrite(D4, LOW);
      digitalWrite(D5, LOW);
      break;
    case 4:
      digitalWrite(D6, LOW);
      digitalWrite(D3, LOW);
      digitalWrite(D4, HIGH);
      digitalWrite(D5, LOW);
      break;
    case 5:
      digitalWrite(D6, HIGH);
      digitalWrite(D3, LOW);
      digitalWrite(D4, HIGH);
      digitalWrite(D5, LOW);
      break;
    case 6:
      digitalWrite(D6, LOW);
      digitalWrite(D3, HIGH);
      digitalWrite(D4, HIGH);
      digitalWrite(D5, LOW);
      break;
    case 7:
      digitalWrite(D6, HIGH);
      digitalWrite(D3, HIGH);
      digitalWrite(D4, HIGH);
      digitalWrite(D5, LOW);
      break;
    case 8:
      digitalWrite(D6, LOW);
      digitalWrite(D3, LOW);
      digitalWrite(D4, LOW);
      digitalWrite(D5, HIGH);
      break;
    case 9:
      digitalWrite(D6, HIGH);
      digitalWrite(D3, LOW);
      digitalWrite(D4, LOW);
      digitalWrite(D5, HIGH);
      break;
    case 0:
      digitalWrite(D6, LOW);
      digitalWrite(D3, LOW);
      digitalWrite(D4, LOW);
      digitalWrite(D5, LOW);
      break;
   }
}

Sorry about my english, I usually speak french. :wink: