Arduino Temperature Driven Fan

Schema of Arduino controlled two speeds fan with LCD
Schema of Arduino controlled two speeds fan with LCD

This project is about driving a two speed fan with an Arduino, based on the environment’s temperature.

The project has been designed to help automating an existing fire-based heating system. The idea is that the environment will be warmed faster, by driving heated air into the room with a multi speed fan, while the fire is hot and the surrounding environment not yet.

I wanted to make it a little more interesting by adding a LCD display to show temperature, humidity and fan status, and four buttons to increase and decrease the two temperature values that drive the fan speeds.

Arduino Prototype of Temperature Driven Fan
Arduino Prototype of Temperature Driven Fan

When the temperature is below the lowest temperature threshold, the fan will be running at full speed. With temperatures between the lowest and the highest threshold the fan will be running at half speed and with temperatures above the highest threshold the fan will be off.

This project demonstrates the use of an Arduino (or compatible) micro controller with a temperature and humidity sensor to drive outputs, it demonstrates the usage of a LCD display, push buttons and EEPROM memory storage.

Below I made a short video demo of the resulting prototype.

Two Channels Relay module
Two Channels Relay module

For the electronic components of the project we need:

  • Arduino or similar (eg: Arduino Mini)
  • DHT22 temperature sensor
  • LCD display
  • A two channels relay module
  • Four push buttons
  • Six resistors – Four 10kΩ as pull-down for the buttons and two resistors for the LCD brightness. In my case the LCD resistors were 1kΩ with 4.7kΩ, with a different LCD and setup I used a 1.5kΩ resistor instead of the 4.7kΩ, it might depend on the LCD manufacturer and on the environment. Alternatively, a potentiometer can be used.

For the software I used four libraries, two of them need to be installed:

For libraries installation please refer to Arduino’s official guide.

Temperature and Humidity - Serial Output
Temperature and Humidity – Serial Output

EasyButton is helpful to read buttons and complete an automatic de-bounce. It is not strictly necessary as it is possible to read and de-bounce buttons manually, but it requires a bit more coding.

DHTlib helps reading the temperature and humidity values of the DHT22 sensor.

Additionally we use the EEPROM library to store the thresholds into the Arduino’s EEPROM, so that even if the Arduino is powered off, the values can be re-loaded at boot.

Finally we use the LiquidCrystal library to drive the LCD display.

To build (and eventually modify the project) you would need to connect all the components according to the schema and load the code into the Arduino microcontroller.

If no text is visible on your LCD display, you can connect a potentiometer to GND, LCD V0 (3rd pin of LCD) and Vcc, instead of the two fixed resistors of the schema, so that the screen brightness can be adjusted if/when needed.

The code built and used on this project can be found on the GitHub gist below:

6 thoughts on “Arduino Temperature Driven Fan”

  1. I used your project to build a homemade fridge to brew beer, instead of a DHT22 I used a waterproof DS18B20. It worked perfectly
    Thank you!

  2. Thank you Mike for your feedback and kind words! It is awesome and rewarding to see that my project was useful to others too, and even better when for completely different purposes!

  3. My son was in a Digital Electronics class in high school this year. He used this as his Year end project and got an A. It is going to be used to cool an overclocked PS4 that gets hot regularly. Thank you for posting!

  4. Hi Enrico, thank you for sharing this nice project. I have replaced DTH with SHT21 and now i have a problem with displaying real time Temp. and Hum. values. When sys started temp. and hum. is displayed and it stays(values) that way all the time…



    // board led
    const int board_led = 13;

    // eeprom value
    byte eeprom_value;

    // timer for sensor and delay
    long last_read_from_sensor = 0;
    const long sensor_read_delay = 1000;

    // maximum and minimum
    const int min_value = 0;
    const int max_value = 50;

    // first value
    const int first_value_up_pin = 3;
    const int first_value_down_pin = 4;

    int first_value = 13;
    const int eeprom_address_first_value = 0;

    // second value
    const int second_value_up_pin = 5;
    const int second_value_down_pin = 6;

    int second_value = 22;
    const int eeprom_address_second_value = 1;

    // lcd setup
    LiquidCrystal_I2C lcd(0x27,16,2); // Set the LCD I2C address

    // outputs
    const int first_output_pin = 2;
    const int second_output_pin = 15;

    // buttons setup
    EasyButton button_first_up(first_value_up_pin);
    EasyButton button_first_down(first_value_down_pin);
    EasyButton button_second_up(second_value_up_pin);
    EasyButton button_second_down(second_value_down_pin);

    // temperature setup
    double current_temperature;
    double current_humidity;

    // configurable lcd messages setup
    const char *message[] = {
    “Loading…”, // loading screen
    “Max”, // max output speed
    “Min”, // min output speed
    “Off”, // off message
    “T”, // temperature
    “H” // humidity

    void setup()
    // write boot message on lcd
    lcd.init(); //initialize the lcd
    lcd.backlight(); //open the backlight
    lcd.begin(16, 2);
    lcd.setCursor(0, 1);

    // turn off board led
    pinMode(board_led, OUTPUT);
    digitalWrite(board_led, LOW);

    // set the two outputs as high
    pinMode(first_output_pin, OUTPUT);
    digitalWrite(first_output_pin, HIGH);
    pinMode(second_output_pin, OUTPUT);
    digitalWrite(second_output_pin, HIGH);

    // initialise serial

    // load first value from eeprom
    eeprom_value =;
    if(eeprom_value != 255)
    first_value = eeprom_value;

    // load second value from eeprom
    eeprom_value =;
    if(eeprom_value != 255)
    second_value = eeprom_value;

    // print two temperature intervals on lcd
    printIntervals(first_value, second_value);

    void loop()
    // read buttons

    // increase value if it is high, if it is less than the maximum value, and the first value is less than the second one
    if(button_first_up.IsPushed() && first_value < max_value && first_value min_value)
    // decrease first_value
    // write on eeprom
    EEPROM.write(eeprom_address_first_value, first_value);
    // update two temperature intervals on lcd
    printIntervals(first_value, second_value);

    // increase value if it is high and if it is less than the maximum value
    if(button_second_up.IsPushed() == HIGH && second_value min_value && first_value sensor_read_delay)


    current_temperature = SHT2x.GetTemperature();
    current_humidity = SHT2x.GetHumidity();

    Serial.print(F(“current temperature: “));

    Serial.print(F(“Current humidity: “));

    // print temperature values on lcd
    printTemperature(current_temperature, current_humidity);

    // turn outputs on/off according to logic
    if(current_temperature first_value && current_temperature < second_value)
    // temperature between two values
    Serial.println(F("Between values"));

    // print speed on lcd

    // half speed
    digitalWrite(first_output_pin, LOW);
    digitalWrite(second_output_pin, HIGH);
    // temperature higher/equal second_value
    Serial.println(F("More than second value"));

    // print speed on lcd

    // off
    digitalWrite(first_output_pin, HIGH);
    digitalWrite(second_output_pin, HIGH);


    // set the last read as now…
    last_read_from_sensor = millis();

    void printIntervals(int t1, int t2) {
    lcd.setCursor(8, 0);
    lcd.print(F(" "));
    // add additional spaces if we have less digits than expected on either temperatures
    if(t1 < 10) lcd.print(F(" "));
    if(t2 -10) lcd.print(F(” “));
    lcd.print(temperature, 1);
    // if only one digit, add final space
    if(temperature > -10 && temperature -10 && humidity 0) {
    for(int i = 0; i < spaces; i++) {
    lcd.print(F(" "));

  5. Hi Matic,

    Not a problem at all, I am glad you liked it!
    Personally I do not have direct experience with SHT sensors. From a quick reading it looks like you need 4 wires and you need to define the sensor variable, passing the data and clock pins.

    My suggestion is to get a simple example working with your sensor, verifying the readings by logging them on the Arduino console. Once you get that working, try to apply the changes to my code to get the full project working with a different sensor.

    Hope it helps and good luck!

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