[原创] 【Nucleo心得】+脉搏心率监测实验

anning865 2014-10-10 22:37 楼主

首先感谢论坛的这次团购，让我们可以使用ST的Nucleo开发板来尽情发挥自己的设计。

之前玩过ST的几块discovery板子，功能都很强大，板子上都有一些可以体现其芯片特色的外设设备。而这次拿到的Nucleo开发板的设计理念并不一样，其并没有扩展外设，而是将接口尽可能地自由发挥出来，留给了用户更大的自由度。其接口兼容arduino板子接口，而编程环境可以使用Mbed网上平台，风格十分类似arduino,因此玩过arduino的玩家可以很快上手mbed开发平台，将其原有的arduino设计轻松转移到Mbed平台。
之前已经在Mbed平台下玩过了KL25Z开发板，发现Mbed平台具有诸多优点，无需安装，驱动完备，程序可导出在keil等平台下调试。最近更是看到ARM公司对MBED的长远规划，感觉这个平台会极大推动物联网的发展，个人比较看好，认为有替代arduino等开源平台的潜力，是实现快速成型的好平台。其他的优点就不说了，希望大家有时间和精力可以好好了解。
言归正传，本实验使用开源脉搏心率传感器Pulse sensor配合NUCLEO-L053R8开发板实现心率监测，并在电脑上显示脉搏曲线和心率数值。pulse sensor采集脉搏的原理是使用515nm波长的绿光照射人体皮肤，由于皮肤内的血液随心脏搏动而造成反射光也出现波动，从而探测到脉搏变化，通过记录相邻两个波峰之间的时间差来计算出心率数值。
先给出两个物品的图片：

传感器一共三个引脚：模拟输出，电源输入，地
按照下面将其连接到开发板上：
pulsesensor-NUCLEO-L053R8
VOUT    ->    A0
VCC       <-    3.3V
GND       <-    GND

将原有的arduino程序移植过来，如下：

#include "mbed.h"
#define false 0
#define true 1
Ticker tick;
DigitalOut led1(LED1);
//DigitalOut led2(PTA13);
AnalogIn pulsepin(A0);//analog input pin
Serial pc(SERIAL_TX, SERIAL_RX);//USB TO SERIAL
// these variables are volatile because they are used during the shorterrupt service routine!
volatile short BPM; // used to hold the pulse rate
volatile short Signal; // holds the incoming raw data
volatile short IBI = 600; // holds the time between beats, must be seeded!
volatile char Pulse = false; // true when pulse wave is high, false when it's low
volatile char QS = false; // becomes true when Arduoino finds a beat.
volatile short 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 short P =512; // used to find peak in pulse wave, seeded
volatile short T = 512; // used to find trough in pulse wave, seeded
volatile short thresh = 512; // used to find instant moment of heart beat, seeded
volatile short amp = 100; // used to hold amplitude of pulse waveform, seeded
volatile char firstBeat = true; // used to seed rate array so we startup with reasonable BPM
volatile char secondBeat = false; // used to seed rate array so we startup with reasonable BPM
//void ledFadeToBeat()
//{
// fadeRate -= 15; // set LED fade value
// fadeRate = constrain(fadeRate,0,255); // keep LED fade value from going shorto negative numbers!
// analogWrite(fadePin,fadeRate); // fade LED
//}
void timer_isr(void)
{
//cli(); // disable shorterrupts while we do this
Signal = pulsepin.read_u16()>>6; // read the Pulse Sensor
sampleCounter += 2; // keep track of the time in mS with this variable
short 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 poshort in pulse wave
}
}
if(Signal > thresh && Signal > P) { // thresh condition helps avoid noise
P = Signal; // P is the peak
} // keep track of highest poshort 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
led1=1; // turn on pin 13 LED
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
for(short 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
//sei(); // enable shorterrupts again
return; // IBI value is unreliable so discard it
}
// keep a running total of the last 10 IBI values
unsigned short runningTotal = 0; // clear the runningTotal variable
for(short 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 shorto 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
led1=0; // turn off pin 13 LED
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 = 512; // 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
}
//sei(); // enable shorterrupts when youre done!
}
void sendDataToProcessing(char symbol, short data )
{
pc.putc(symbol); // symbol prefix tells Processing what type of data is coming
pc.printf("%d\r\n", data); // the data to send culminating in a carriage return
}
int main()
{
pc.baud(115200); // we agree to talk fast!
tick.attach_us(&timer_isr,2000); // sets up to read Pulse Sensor signal every 2mS
while(1) {
sendDataToProcessing('S', Signal); // send Processing the raw Pulse Sensor data
if (QS == true) { // Quantified Self flag is true when arduino finds a heartbeat
//fadeRate = 255; // Set 'fadeRate' Variable to 255 to fade LED with pulse
sendDataToProcessing('B',BPM); // send heart rate with a 'B' prefix
sendDataToProcessing('Q',IBI); // send time between beats with a 'Q' prefix
QS = false; // reset the Quantified Self flag for next time
}
//ledFadeToBeat();
wait(0.02); // take a break
}
}

MBED平台下载程序很简单，只需要将编译产生的文件拖进开发板在电脑上显示的U盘空间中就可以了。
程序中以500hz频率进行AD采集，将数据滤波处理后通过串口发送到电脑上，同时板子上的LD2小灯会跟随心跳频率闪烁。
上位机软件采用开源软件processing，程序可以在pulsesensor官网下载得到。直接运行后可以看到采集到脉搏波形和心率数值。