// --- CONSTANTS & CONFIGURATION ---
const float BETA = 3950;       // Beta Coefficient for the Wokwi NTC Thermistor
const int SENSOR_PIN = A0;     // Temperature sensor connected to Analog A0
const int RELAY_PIN = 13;      // Relay control pin connected to Digital 13
const float TEMP_THRESHOLD = 40.0; // The threshold temperature

void setup() {
  // Set the relay pin as an output
  pinMode(RELAY_PIN, OUTPUT);
  
  // Start Serial communication for debugging
  Serial.begin(9600);
}

void loop() {
  // 1. READ SENSOR
  int analogValue = analogRead(SENSOR_PIN);
  
  // 2. CALCULATE TEMPERATURE (NTC BETA EQUATION)
  // This formula converts the non-linear resistance of the NTC to Celsius
  float celsius = 1 / (log(1 / (1023.0 / analogValue - 1)) / BETA + 1.0 / 298.15) - 273.15;
  
  // 3. DEBUGGING (View this in the Serial Monitor)
  Serial.print("Current Temp: ");
  Serial.print(celsius);
  Serial.println(" °C");

  // 4. LOGIC CONTROL
  // Requirement: Buzzer ON if temp is LESS than 40 (< 40)
  if (celsius < TEMP_THRESHOLD) {
    digitalWrite(RELAY_PIN, HIGH); // Relay ON (Circuit Closed -> Buzzer Sounds)
  } else {
    digitalWrite(RELAY_PIN, LOW);  // Relay OFF (Circuit Open -> Buzzer Silent)
  }

  // Small delay to stabilize readings
  delay(500); 
}