Heart Beat Monitoring using PIC Microcontroller and Pulse Sensor

/*
 * File:   main.c
 * Author: Sourav Gupta
 * By:- circuitdigest.com
 * Created on September 30, 2018, 2:26 PM
 */

// PIC16F877A Configuration Bit Settings

// 'C' source line config statements

// CONFIG
#pragma config FOSC = HS        // Oscillator Selection bits (HS oscillator)
#pragma config WDTE = OFF       // Watchdog Timer Enable bit (WDT disabled)
#pragma config PWRTE = OFF      // Power-up Timer Enable bit (PWRT disabled)
#pragma config BOREN = ON       // Brown-out Reset Enable bit (BOR enabled)
#pragma config LVP = OFF         // Low-Voltage (Single-Supply) In-Circuit Serial Programming Enable bit (RB3/PGM pin has PGM function; low-voltage programming enabled)
#pragma config CPD = OFF        // Data EEPROM Memory Code Protection bit (Data EEPROM code protection off)
#pragma config WRT = OFF        // Flash Program Memory Write Enable bits (Write protection off; all program memory may be written to by EECON control)
#pragma config CP = OFF         // Flash Program Memory Code Protection bit (Code protection off)

#include <xc.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <stdbool.h>
#include "supporing_cfile\lcd.h"
#include "supporing_cfile\eusart1.h"
#include "supporing_cfile\adc.h"
#include "supporing_cfile\tmr0.h"

/*
 Hardware related definition
 */
#define _XTAL_FREQ 200000000 //Crystal Frequency, used in delay

/*
 Program Flow related definition
 */

#define READ_ADC  1
#define CALCULATE_HEART_BEAT 2
#define SHOW_HEART_BEAT 3
#define IDLE 0
#define DEFAULT -1

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 bool firstBeat = true; // used to seed rate array so we startup with reasonable BPM
volatile bool secondBeat = false; // used to seed rate array so we startup with reasonable BPM

volatile int BPM; // int that holds raw Analog in 0. updated every 2mS
volatile int Signal; // holds the incoming raw data
volatile int IBI = 600; // int that holds the time interval between beats! Must be seeded!
volatile bool Pulse = false; // "True" when User's live heartbeat is detected. "False" when not a "live beat".
volatile bool QS = false; // becomes true when finds a beat.

int main_state = -1;
int adc_value = 0;

int tune = 0;
/*
 Other Specific definition
 */
void system_init(void);

void calculate_heart_beat(int adc_value) {

    Signal = adc_value;

    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
            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
                int i;
                for (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
                //pulse_tmr_handle = bsp_harmony_start_tmr_cb_periodic(PULSE_CHECK_TIME_INTERVAL, 0, pulse_read_cb); // enable interrupts again
                return; // IBI value is unreliable so discard it
            }

            // keep a running total of the last 10 IBI values
            uint16_t runningTotal = 0; // clear the runningTotal variable
            int i;
            for (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
        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
    }

}

void main() {

    system_init();
    main_state = READ_ADC;        
    while (1) {
        switch (main_state) {
            case READ_ADC:
            {                
                adc_value = ADC_Read(0);
                main_state = CALCULATE_HEART_BEAT;                
                break;
            }
            case CALCULATE_HEART_BEAT:
            {
                calculate_heart_beat(adc_value);
                main_state = SHOW_HEART_BEAT;
                break;
            }
            case SHOW_HEART_BEAT:
            {
                if (QS == true) { // A Heartbeat Was Found
                    // BPM and IBI have been Determined
                    // Quantified Self "QS" true when arduino finds a heartbeat                    
                    QS = false; // reset the Quantified Self flag for next time

                    // 0.9 used for getting better data. actually should not be used
                    //BPM = BPM * 0.9;
                   // IBI = IBI / 0.9;                    
                    //IBI = IBI * 2;
                   // tune = BPM / 2;
                    //lcd_com(0x01);                    
                    lcd_com(0x80);                  
                    lcd_puts("BPM:-     ");
                    lcd_print_number(BPM);
                    lcd_puts (" ");
                    lcd_com(0xC0);
                    lcd_puts("I.B.I:-   ");
                    lcd_print_number(IBI);
                    lcd_puts (" ");
                    
                }
            }

                main_state = IDLE;
                break;
        
        case IDLE:
        {            
            break;
        }
        default:
        {

        }
    }
}
}
/*
 This Function is for system initializations.
 */

void system_init(void){
    TRISB = 0x00;
    lcd_init(); // This will initialize the lcd
    TMR0_Initialize();
    TMR0_StartTimer();
    INTERRUPT_GlobalInterruptEnable();
    INTERRUPT_PeripheralInterruptEnable();   
    ADC_Init();
}

/*
 * Custom timer callback function
 */

void timer_isr() {
    main_state = READ_ADC;    
}

void interrupt INTERRUPT_InterruptManager (void)
{
    // interrupt handler
    if(INTCONbits.TMR0IE == 1 && INTCONbits.TMR0IF == 1)
    {
        TMR0_ISR();
    }
}