Heart rate measurement from fingertip. Part 2. Software

Part 1. Schematic

Software

The firmware does all the control and computation operation. In order to save the power, the sensor module is not activated continuously. Instead, it is turned on for 15 sec only once the start button is pressed. The pulses arriving at T0CKI are counted through Timer0 module operated in counter mode without prescaler. The complete program written for MikroC compiler (mikroElektronika) is provided below. An assembled HEX file is also available to download.

/*
  Project: Measuring heart rate through fingertip
  Copyright @ Rajendra Bhatt
  January 18, 2011
  PIC16F628A at 4.0 MHz external clock, MCLR enabled
*/

sbit IR_Tx at RA3_bit;
sbit DD0_Set at RA2_bit;
sbit DD1_Set at RA1_bit;
sbit DD2_Set at RA0_bit;
sbit start at RB7_bit;
unsigned short j, DD0, DD1, DD2, DD3;
unsigned short pulserate, pulsecount;
unsigned int i;
//-------------- Function to Return mask for common anode 7-seg. display
unsigned short mask(unsigned short num) {
 switch (num) {
 case 0 : return 0xC0;
 case 1 : return 0xF9;
 case 2 : return 0xA4;
 case 3 : return 0xB0;
 case 4 : return 0x99;
 case 5 : return 0x92;
 case 6 : return 0x82;
 case 7 : return 0xF8;
 case 8 : return 0x80;
 case 9 : return 0x90;
 } //case end
}

void delay_debounce(){
 Delay_ms(300);
}

void delay_refresh(){
 Delay_ms(5);
}

void countpulse(){
 IR_Tx = 1;
 delay_debounce();
 delay_debounce();
 TMR0=0;
 Delay_ms(15000);  // Delay 15 Sec
 IR_Tx = 0;
 pulsecount = TMR0;
 pulserate = pulsecount*4;
}

void display(){
  DD0 = pulserate%10;
  DD0 = mask(DD0);
  DD1 = (pulserate/10)%10;
  DD1 = mask(DD1);
  DD2 = pulserate/100;
  DD2 = mask(DD2);
  for (i = 0; i<=180*j; i++) {
    DD0_Set = 0;
    DD1_Set = 1;
    DD2_Set = 1;
    PORTB = DD0;
    delay_refresh();
    DD0_Set = 1;
    DD1_Set = 0;
    DD2_Set = 1;
    PORTB = DD1;
    delay_refresh();
    DD0_Set = 1;
    DD1_Set = 1;
    DD2_Set = 0;
    PORTB = DD2;
    delay_refresh();
    }
  DD2_Set = 1;
}

void main() {
 CMCON = 0x07;    // Disable Comparators
 TRISA = 0b00110000; // RA4/T0CKI input, RA5 is I/P only
 TRISB = 0b10000000; // RB7 input, rest output
 OPTION_REG = 0b00101000; // Prescaler (1:1), TOCS =1 for counter mode
 pulserate = 0;
 j = 1;
 display();
 do {
  if(!start){
   delay_debounce();
   countpulse();
   j= 3;
   display();
  }
 } while(1);  // Infinite loop
}

Downloads

Source Code and hex - download

Part 3. References, notes, using the device.

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