Arduino Temperature Controlled Fan

1. Introduction

A Temperature Controlled Fan is an intelligent system that automatically turns ON or adjusts the speed of a fan based on ambient temperature. This project uses an Arduino Uno and an LM35 Temperature Sensor to monitor temperature and control a fan.

This is widely used in:

Electronic cooling systems
Smart homes
Industrial automation
Computer CPU cooling

2. Components Required

Arduino Uno
LM35 Temperature Sensor
DC Fan (5V or 12V)
NPN Transistor (TIP122)
Diode (1N4007)
Resistor (1kΩ)
External Power Supply (if needed)
Breadboard
Connecting Wires

3. Circuit and Connections

Circuit Diagram Temperature Controlled Fan

Pinout Diagram of Arduino Uno

LM35 Pinout Diagram

Connections:

LM35 Sensor:

VCC → 5V
GND → GND
OUT → A0

Fan Control:

Fan + → External Supply (+)
Fan – → Collector of Transistor
Emitter → GND
Base → Arduino Pin 9 (via 1kΩ resistor)

Protection:

Diode across fan (reverse biased)

4. Detailed Step By Step Circuit Working

LM35 senses temperature and outputs analog voltage
Arduino reads this voltage from A0
Converts voltage into temperature (°C)
Compares temperature with threshold
If temperature exceeds limit → Fan turns ON
If temperature is low → Fan remains OFF

Optional:

Use PWM to control fan speed dynamically

5. Libraries to be Included

No external libraries required ✅

6. Code


#define tempPin A0
#define fanPin 9

float temperature = 0;

void setup() {
  pinMode(fanPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  int value = analogRead(tempPin);
  float voltage = value * (5.0 / 1023.0);
  temperature = voltage * 100;

  Serial.print("Temperature: ");
  Serial.println(temperature);

  if (temperature > 30) {
    digitalWrite(fanPin, HIGH);
  } else {
    digitalWrite(fanPin, LOW);
  }

  delay(1000);
}

7. Detailed Step By Step Code Working

analogRead(A0) → Reads sensor value
Converts to voltage
LM35 gives 10mV per °C
Temperature = Voltage × 100
If temperature > 30°C → Fan ON
Else → Fan OFF

8. Output

Fan automatically starts when temperature rises
Stops when temperature drops
Can be upgraded to variable speed

9. Applications

CPU Cooling Systems
Smart Home Automation
Industrial Machines
Battery Cooling Systems
Greenhouses

10. Advantages

Energy efficient
Automatic operation
Low cost
Easy to build
Expandable to IoT

11. Disadvantages

Basic version has fixed threshold
LM35 limited temperature range
Fan speed control not included (in basic model)

12. Future Improvements

Add LCD display
Use PWM for speed control
Add IoT monitoring (Blynk)
Use DHT11 Sensor for humidity + temperature
Mobile app control