心跳率是監測任何人健康狀況的最重要參數。在可穿戴設備的現代時代，有很多設備可以測量心跳、血壓、腳步聲、燃燒的卡路里和許多其他東西。這些設備內部有脈沖傳感器來感應脈搏率。今天，我們還將使用帶有PIC微控制器的脈沖傳感器來計算每分鐘的心跳次數和心跳間隔，這些值將進一步顯示在16x2字符LCD上。我們將在本項目中使用PIC16F877A PIC微控制器。我們已經將脈沖傳感器與Arduino連接起來，用于患者監測系統。

必需組件

PIC16F877A 微控制器

20 兆赫晶體

33pF電容 2個

4.7k 電阻器 1 個

16x2 字符液晶顯示器

10K 電位器，用于 LCD 的對比度控制

SEN-11574 脈沖傳感器

魔術貼帶

5V電源適配器

面包板和連接線

脈沖傳感器 SEN-11574

為了測量心跳，我們需要一個脈搏傳感器。在這里，我們選擇了SEN-11574脈沖傳感器，它可以在網上或線下商店輕松買到。我們使用此傳感器是因為制造商提供了示例代碼，但那是Arduino代碼。我們為PIC微控制器轉換了該代碼。

該傳感器非常小，非常適合通過耳垂或指尖讀取心跳。它的直徑為 0.625“，圓形 PCB 側的厚度為 0.125”。

該傳感器提供模擬信號，傳感器可由3V或5V驅動，傳感器的電流消耗為4 mA，非常適合移動應用。傳感器配有三根電線，末端帶有 24 英寸長的連接電纜和 berg 公接頭。此外，傳感器還配有魔術貼指帶，可將其佩戴在指尖上。

脈沖傳感器原理圖也由制造商提供，也可在 sparkfun.com 上購買。

傳感器原理圖由光學心率傳感器、降噪RC電路或濾波器組成，如原理圖所示。R2、C2、C1、C3 和運算放大器 MCP6001 用于可靠的放大模擬輸出。

用于心跳監測的其他傳感器很少，但SEN-11574脈沖傳感器廣泛用于電子項目。

脈沖傳感器與PIC微控制器接口的電路圖

在這里，我們已經連接了脈沖傳感器跨 2德·微控制器的引腳單位。由于傳感器提供模擬數據，我們需要通過進行必要的計算將模擬數據轉換為數字信號。

20Mhz的晶體振蕩器通過兩個陶瓷33pF電容器連接在微控制器單元的兩個OSC引腳上。液晶屏通過微控制器的RB端口連接。

PIC16F877A 心跳監護儀代碼說明

對于初學者來說，代碼有點復雜。制造商提供了SEN-11574傳感器的示例代碼，但它是為Arduino平臺編寫的。我們需要轉換微芯片 PIC16F877A 的計算結果。本項目結束時將提供完整的代碼，并附有演示視頻。并且可以從此處下載支持的C文件。

我們的代碼流相對簡單，我們使用開關大小寫來執行步驟。根據制造商的說法，我們需要每 2 毫秒從傳感器獲取數據。因此，我們使用了計時器中斷服務例程，它將每 2 毫秒觸發一個函數。

switch語句中的代碼流將如下所示：

案例1：讀取ADC

案例2：計算心跳和IBI

情況 3：在液晶屏上顯示心跳和 IBI

案例 4：空閑（不執行任何操作）

在定時器中斷功能中，我們將程序的狀態更改為情況 1：每 2 毫秒讀取一次 ADC。

因此，在 main 函數中，我們定義了程序狀態和所有開關情況。

void main() {

system_init();

main_state = READ_ADC;

while (1) {

switch (main_state) {

case READ_ADC:

{

adc_value = ADC_Read(0); // 0 is the channel number

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;

lcd_com(0x80);

lcd_puts("BPM:- ");

lcd_print_number(BPM);

lcd_com(0xC0);

lcd_puts("I.B.I:- ");

lcd_print_number(IBI);

}

}

main_state = IDLE;

break;

case IDLE:

{

break;

}

default:

{

}

}

}

}

我們使用 PIC16F877A 的兩個硬件外設：定時器0 和 ADC。

在 timer0.c 文件中，

TMR0 = (uint8_t)(tmr0_mask & (256-(((2 *_XTAL_FREQ)/(256*4))/1000)));

此計算提供 2 毫秒計時器中斷。計算公式為

// TimerCountMax - (((delay(ms) * Focs(hz)) / (PreScale_Val * 4)) / 1000)

如果我們看到timer_isr函數，它是-

void timer_isr() {

main_state = READ_ADC;

}

在此函數中，程序狀態每 2ms 更改為 READ_ADC。

然后，CALCULATE_HEART_BEAT函數取自 Arduino 示例代碼。

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

}

}

………….

………………………..

此外，下面給出了完整的代碼，并通過注釋進行了很好的解釋。這種心跳傳感器數據可以進一步上傳到云端，并從任何地方通過互聯網進行監控，從而使其成為基于物聯網的心跳監測系統。

/*

* 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

#include

#include

#include

#include

#include "supporing_cfilelcd.h"

#include "supporing_cfileeusart1.h"

#include "supporing_cfileadc.h"

#include "supporing_cfiletmr0.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();

}

}