const int LDR_PIN = A0;  
const int BUTTON_PIN = 2; 

volatile bool displayLDR = false; 

void buttonISR() {
  Serial.println("Button Pressed!");  // Debugging message
  displayLDR = !displayLDR;
}

void setup() {
  Serial.begin(9600);
  pinMode(BUTTON_PIN, INPUT);  // Use INPUT (because external pull-down resistor is used)
  attachInterrupt(digitalPinToInterrupt(BUTTON_PIN), buttonISR, RISING); // Detect press

  Serial.println("System Initialized. Press button to start/stop readings.");
}

void loop() {
  if (displayLDR) {
    int lightLevel = analogRead(LDR_PIN);
    if (lightLevel < 0 || lightLevel > 1023) { 
      Serial.println("Reading Error"); 
    } else {
      Serial.print("Light Level: ");
      Serial.println(lightLevel);
    }
    delay(500);
  }
}