// Include the necessary libraries
#include <OneWire.h>
#include <DallasTemperature.h>

// Set up the temperature sensor
#define ONE_WIRE_BUS 2
OneWire oneWire(ONE_WIRE_BUS);
DallasTemperature sensors(&oneWire);

// Set up the relay module
int relayPin = 3;

// Set up the LED
int ledPin = 4;

void setup() {
  // Initialize the temperature sensor
  sensors.begin();

  // Initialize the relay module and LED
  pinMode(relayPin, OUTPUT);
  pinMode(ledPin, OUTPUT);
}

void loop() {
  // Read the temperature from the sensor
  sensors.requestTemperatures();
  float temperature = sensors.getTempCByIndex(0);

  // If the temperature is above a certain threshold, turn on the fan
  if (temperature > 25) {
    digitalWrite(relayPin, HIGH);
    digitalWrite(ledPin, HIGH);
  } 
  // Otherwise, turn off the fan
  else {
    digitalWrite(relayPin, LOW);
    digitalWrite(ledPin, LOW);
  }

  // Wait for a short period of time before taking another temperature reading
  delay(1000);
}