This is a very simple coding to make an temperature-controlled automatic fan. It will display the temperature at the 16 X 2 LCD screen. When the temperature is more than 35 degree celcius, it will trigger the relay and get the DC fan to ON.

Temperature-Controlled DC Fan

#include <LiquidCrystal.h>
int reading = 0;
int sensorPin = A0;
int relay =7;
// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

void setup() {
  // set up the LCD's number of columns and rows: 
  lcd.begin(16, 2);
  // Print a message to the LCD.
 pinMode(relay,OUTPUT);
}

void loop() {
  // set the cursor to column 0, line 1
  // (note: line 1 is the second row, since counting begins with 0):
  reading = analogRead(sensorPin);
 int celsius = reading/2;
  lcd.setCursor(0, 0);
  lcd.print("Temperature: ");
  // print the number of seconds since reset:
  lcd.setCursor(0,1);
  lcd.print(celsius, DEC);
  lcd.print((char)223);
  lcd.print("C");
  if (celcius >35)
  {
    digitalWrite(7,HIGH);
  }
  else
  
  {digitalWrite(7,LOW);
  }
  delay(500);
  lcd.clear();
}