#include<LiquidCrystal_I2C.h>

const int buttonPin = 2;
int buttonState = 0;
int previousButtonState = LOW;
unsigned long startTime;
int pulseCount = 0;

LiquidCrystal_I2C lcd(0x27,16,2);

void setup() {
  lcd.init();
  lcd.backlight();
  pinMode(buttonPin, INPUT);
  Serial.begin(9600);
  startTime = millis();
}

void loop() {
    buttonState = digitalRead(buttonPin);
    
    // Check if button is pressed
    if (buttonState == HIGH && previousButtonState == LOW) {
      pulseCount++;
      delay(50);    
    }
    previousButtonState = buttonState;
    // Check if 15 seconds have passed
    if (millis() - startTime >= 60000) {
        // Calculate BPM: multiply count by 4 to estimate BPM for 15s interval
        double bpm = (double)pulseCount/120;
        
        // Output BPM to Serial Monitor
        Serial.print("BPM: ");
        lcd.print("BPM: ");
        Serial.println(bpm);
        lcd.print(bpm);     
        delay(2000);
        lcd.clear();
        // Reset variables for next measurement
        pulseCount = 0;
        startTime = millis();
    }
}