● 아두이노 심박센서(XD-58C)는 심박수를 측정할 수 있는 센서 모듈로 주로 생체 신호 모니터링에 사용된다.
● 센서 중앙에는 밝은 초록 빛이 방출되며 심장이 박동할 때
    혈류가 증가하면 반사되어 돌아오는 빛의 양이 줄어드는 것을 활용하여 심박수를 측정한다.

---<  XD-58C_Pulse-Sensor_BCM-Monitor.ino  >----------------------------------------
#define USE_ARDUINO_INTERRUPTS true    // Set-up low-level interrupts for most acurate BPM math.
#include <PulseSensorPlayground.h>    // Includes the PulseSensorPlayground Library. 

//  Variables
const int PulseWire = 0;      // PulseSensor PURPLE WIRE connected to ANALOG PIN 0
const int LED = 9;          // The on-board Arduino LED, close to PIN 13.
int Threshold = 550;          // Determine which Signal to "count as a beat" and which to ignore.
                             
PulseSensorPlayground pulseSensor;  // Creates an instance of the PulseSensorPlayground object called "pulseSensor"

void setup() { 

  Serial.begin(9600);          // For Serial Monitor

  // Configure the PulseSensor object, by assigning our variables to it.
  pulseSensor.analogInput(PulseWire); 
  pulseSensor.blinkOnPulse(LED);      //auto-magically blink Arduino's LED with heartbeat.
  pulseSensor.setThreshold(Threshold); 

  // Double-check the "pulseSensor" object was created and "began" seeing a signal.
  if (pulseSensor.begin()) {
    Serial.println("We created a pulseSensor Object !");  //This prints one time at Arduino power-up,  or on Arduino reset. 
  }
}

void loop() {

  int myBPM = pulseSensor.getBeatsPerMinute();  // Calls function on our pulseSensor object that returns BPM as an "int".

  if (pulseSensor.sawStartOfBeat()) {            // Constantly test to see if "a beat happened".
      Serial.println("♥  A HeartBeat Happened ! "); // If test is "true", print a message "a heartbeat happened".
      Serial.print("BPM: ");                        // Print phrase "BPM: "
      Serial.println(myBPM);                        // Print the value inside of myBPM.
  }

  delay(20);                    // considered best practice in a simple sketch.
}