手指偵測心跳模組

科易KEYES 手指偵測心跳模組

專案說明

使用「科易KEYES Arduino UNO R3 開發板」連接「手指偵測心跳模組」,讀取手指偵測心跳速率。

此科易手指偵測心跳模組包含於「科易KEYES 手指偵測心跳模組」內。

KEYES Arduino UNO R3電路圖

· KEYES Arduino UNO R3

· 科易KEYES 手指偵測心跳模組

手指偵測心跳模組是類比訊號輸入,可以接「A0 ~ A5」的KEYES Arduino UNO R3訊號端上。 本範例連接到「A0」。

手指偵測心跳模組上S部分的腳位接到Arduino端的S、中間再接V端、-腳位接到GND。

手指偵測心跳模組由一個紅外線LED和光敏電晶體所構成,原理是透過手指放在紅外線發射器和光敏電晶體之間後,隨著心臟跳動,光敏電晶體的電阻值也在不斷變化,通過這種變化來檢測心跳。為防止外界光線對資料造成影響,最好將 手指偵測心跳模放在一個封閉的盒子裡或是用套子包住感測器,在進行心跳檢測。

Arduino 程式

如果手指放紅外線LED和光敏電晶體之間時在兩秒間的感測數值有不同的跳動的話,會顯示你目前手指脈搏偵測到的心跳數,沒有數值跳動的話則不會顯示心跳數。

產生出的 Arduino 程式如下

#define samp_siz 4
#define rise_threshold 4
// Pulse Monitor Test Script
int sensorPin = A0;
void setup() {
Serial.begin(9600);
}
void loop ()
{
float reads[samp_siz], sum;
long int now, ptr;
float last, reader, start;
float first, second, third, before, print_value;
bool rising;
int rise_count;
int n;
long int last_beat;
for (int i = 0; i < samp_siz; i++)
reads[i] = 0;
sum = 0;
ptr = 0;
while(1)
{
// calculate an average of the sensor
// during a 20 ms period (this will eliminate
// the 50 Hz noise caused by electric light
n = 0;
start = millis();
reader = 0.;
do
{
reader += analogRead (sensorPin);
n++;
now = millis();
}
while (now < start + 20);
reader /= n; // we got an average
// Add the newest measurement to an array
// and subtract the oldest measurement from the array
// to maintain a sum of last measurements
sum -= reads[ptr];
sum += reader;
reads[ptr] = reader;
last = sum / samp_siz;
// now last holds the average of the values in the array
// check for a rising curve (= a heart beat)
if (last > before)
{
rise_count++;
if (!rising && rise_count > rise_threshold)
{
// Ok, we have detected a rising curve, which implies a heartbeat.
// Record the time since last beat, keep track of the two previous
// times (first, second, third) to get a weighed average.
// The rising flag prevents us from detecting the same rise more than once.
rising = true;
first = millis() - last_beat;
last_beat = millis();
// Calculate the weighed average of heartbeat rate
// according to the three last beats
print_value = 60000. / (0.4 * first + 0.3 * second + 0.3 * third);
Serial.print("心跳數:");
Serial.print(print_value);
Serial.print("\n");
third = second;
second = first;
}
}
else
{
// Ok, the curve is falling
rising = false;
rise_count = 0;
}
before = last;
ptr++;
ptr %= samp_siz;
}
}