PIR Sensor Based Smart Fan Controller with Temperature Sensing

Project Overview

This project creates a smart fan controller that turns on a fan when motion is detected and the room temperature exceeds a set threshold. It is perfect for bathrooms, home offices, or workshops where you want ventilation only when needed.

Difficulty: Intermediate
Estimated time: 2 hours
Estimated cost: $20-30

How It Works

A PIR sensor detects motion, and a DHT22 temperature sensor measures the room temperature. If motion is detected AND the temperature exceeds the threshold (e.g., 26°C), the system activates a relay to turn on the fan. The fan runs for a set time after motion stops.

Materials Needed

• Arduino Uno or Nano (1)
• HC-SR501 PIR sensor (1)
• DHT22 temperature/humidity sensor (1)
• Relay module (5V, rated for fan load)
• LED for status indication
• 220Ω resistor
• Jumper wires
• Power supply (5V 2A)

Circuit Diagram

Connection Table

OUT

Digital Pin 2

DATA

Digital Pin 3

IN

Digital Pin 4

Anode

Digital Pin 13

表

Arduino Code

// Smart Fan Controller with PIR and Temperature Sensor
#include <DHT.h>

#define DHTTYPE DHT22
#define DHTPIN 3

DHT dht(DHTPIN, DHTTYPE);

const int pirPin = 2;
const int relayPin = 4;
const int ledPin = 13;

const float tempThreshold = 26.0; // Celsius

unsigned long lastMotionTime = 0;
const unsigned long fanOffDelay = 600000; // 10 minutes
bool fanOn = false;

void setup() {
  Serial.begin(9600);
  pinMode(pirPin, INPUT);
  pinMode(relayPin, OUTPUT);
  pinMode(ledPin, OUTPUT);
  
  digitalWrite(relayPin, LOW);
  digitalWrite(ledPin, LOW);
  
  dht.begin();
  
  delay(60000);
}

void turnFanOn() {
  digitalWrite(relayPin, HIGH);
  digitalWrite(ledPin, HIGH);
  fanOn = true;
  lastMotionTime = millis();
}

void turnFanOff() {
  digitalWrite(relayPin, LOW);
  digitalWrite(ledPin, LOW);
  fanOn = false;
}

void loop() {
  bool motion = digitalRead(pirPin) == HIGH;
  float temp = dht.readTemperature();
  
  if (isnan(temp)) {
    Serial.println("DHT read error");
    delay(1000);
    return;
  }
  
  if (motion && !fanOn && temp > tempThreshold) {
    turnFanOn();
  }
  
  if (fanOn && motion) {
    lastMotionTime = millis();
  }
  
  if (fanOn && (millis() - lastMotionTime > fanOffDelay)) {
    turnFanOff();
  }
  
  delay(100);
}

Installation Steps

1. Assemble the circuit and test.
2. Mount the PIR sensor to cover the room.
3. Place the DHT22 away from direct airflow.
4. Wire the fan through the relay (AC wiring requires caution).
5. Adjust temperature threshold as desired.
6. Test by entering the room when warm.

Project Extensions

• Add humidity sensing to trigger the fan (bathroom use)
• Add manual override button
• Add Wi-Fi to report temperature and fan status
• Add LCD to display temperature and fan state

Conclusion

This smart fan controller saves energy by running the fan only when needed.