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();
}
}

Video

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