#include <Adafruit_SSD1306.h>
#define OLED_Address 0x3C // 0x3C device address of I2C OLED. Few other OLED has 0x3D
Adafruit_SSD1306 oled(128, 64); // create our screen object setting resolution to 128x64
int a=0;
int lasta=0;
int lastb=0;
int LastTime=0;
int ThisTime;
bool BPMTiming=false;
bool BeatComplete=false;
int BPM=0;
#define UpperThreshold 560
#define LowerThreshold 530

// Definisikan pin buzzer
#define BuzzerPin 5

void setup() {
  oled.begin(SSD1306_SWITCHCAPVCC, OLED_Address);
  oled.clearDisplay();
  oled.setTextSize(2);

  // Setup pin buzzer sebagai output
  pinMode(BuzzerPin, OUTPUT);
}

void loop()
{
  if(a>127)
  {
    oled.clearDisplay();
    a=0;
    lasta=a;
  }

  ThisTime=millis();
  int value=analogRead(0);
  oled.setTextColor(WHITE);
  int b=60-(value/16);
  oled.writeLine(lasta,lastb,a,b,WHITE);
  lastb=b;
  lasta=a;

  if(value > UpperThreshold)
  {
    if(BeatComplete)
    {
      BPM=ThisTime-LastTime;
      BPM=int(60/(float(BPM)/1000));
      BPMTiming=false;
      BeatComplete=false;
      tone(8,1000,250);
    }
    if(BPMTiming == false)
    {
      LastTime=millis();
      BPMTiming=true;
    }
  }

  // Cek jika pulse di bawah LowerThreshold
  if((value < LowerThreshold) && (BPMTiming))
  {
    BeatComplete=true;
    
    // Nyalakan buzzer karena pulse low
    digitalWrite(BuzzerPin, HIGH);
  }
  else
  {
    // Matikan buzzer jika pulse stabil atau menengah
    digitalWrite(BuzzerPin, LOW);
  }

  oled.writeFillRect(0,50,128,16,BLACK);
  oled.setCursor(0,50);
  oled.print("BPM:");
  oled.print(BPM);
  oled.display();
  a++;
}