Temperature-controlled fan

Combine a sensor, a decision and a motor driver into an automatic fan.

Open in Circuit Lab Simulator

Interactive Simulation

Temperature-controlled fanarduino-uno

Open in Lab

Required Components Checklist

Assembly Steps

Sensor

DHT11 data on pin 4, powered from 5V.

Driver

IN1 → pin 7, IN2 → pin 8, EN → pin 5 (PWM). Motor supply from a battery pack; share GND with the Uno.

Control law

Below 25 °C off; 25–35 °C maps to increasing speed; failed readings switch the fan off.

Arduino Sketch

#include <DHT.h>

DHT dht(4, DHT11);
const int IN1 = 7, IN2 = 8, EN = 5;

void setup() {
  Serial.begin(9600);
  dht.begin();
  pinMode(IN1, OUTPUT);
  pinMode(IN2, OUTPUT);
  pinMode(EN, OUTPUT);
  digitalWrite(IN1, HIGH); // always spin the same way
  digitalWrite(IN2, LOW);
}

void loop() {
  float t = dht.readTemperature();
  if (isnan(t)) {
    Serial.println("Sensor error - fan off for safety");
    analogWrite(EN, 0);
  } else {
    int speed = 0;
    if (t >= 25) speed = map(constrain(t, 25, 35), 25, 35, 100, 255);
    analogWrite(EN, speed);
    Serial.print(t);
    Serial.print(" C -> fan ");
    Serial.println(speed);
  }
  delay(2000);
}

Challenges & Extensions

Ready to take this project further? Try these challenges:

•Add a manual override button.
•Show the speed on an LCD.
•Use humidity too: speed up when it's humid.