Complete Guide for DHT11/DHT22 Humidity and Temperature Sensor With Arduino

1 Required Components

Before starting your DHT11/DHT22 project, gather these essential components:

• Arduino Board: Uno, Nano, Mega, or compatible microcontroller
• DHT Sensor: DHT11 or DHT22 temperature and humidity sensor
• Resistor: 10kΩ pull-up resistor (if your sensor module doesn't include one)
• Breadboard: For prototyping and easy connections
• Jumper Wires: Male-to-male for making connections
• USB Cable: For programming and powering the Arduino

2 Wiring Instructions

Follow these connections to wire your DHT sensor to Arduino:

1. Power Connection: Connect DHT Pin 1 (VCC) to Arduino 5V pin
2. Data Connection: Connect DHT Pin 2 (DATA) to Arduino Digital Pin 2
3. Pull-up Resistor: Add a 10kΩ resistor between DHT Pin 1 (VCC) and Pin 2 (DATA)
4. Ground Connection: Connect DHT Pin 4 (GND) to Arduino GND pin
5. No Connection: Leave DHT Pin 3 (NC) unconnected

3 Library Installation Process

The easiest way to work with DHT sensors is through the Adafruit DHT library, which handles all the complex timing and signal processing. You'll also need the Adafruit Unified Sensor Library as a dependency.

1. Open Arduino IDE: Launch the Arduino Integrated Development Environment
2. Access Library Manager: Go to Sketch > Include Library > Manage Libraries
3. Search for DHT Library: Type "DHT sensor library" in the search box
4. Install DHT Library: Find "DHT sensor library by Adafruit" and click Install
5. Install Unified Sensor Library: Search for "Adafruit Unified Sensor" and install it
6. Restart Arduino IDE: Close and reopen the IDE to complete installation

4 Basic Reading Example

Here's the complete code to read temperature and humidity from DHT sensors and display results in the Serial Monitor:

// Complete DHT Sensor Reading Example
// Works with DHT11, DHT22, and DHT21 sensors

#include "DHT.h"

// Configuration - Modify for your setup
#define DHTPIN 2          // Digital pin connected to DHT sensor
#define DHTTYPE DHT11     // DHT 11 
//#define DHTTYPE DHT22   // DHT 22 (AM2302)
//#define DHTTYPE DHT21   // DHT 21 (AM2301)

// Initialize DHT sensor
DHT dht(DHTPIN, DHTTYPE);

void setup() {
  Serial.begin(9600);
  Serial.println("DHTxx sensor test!");
  
  dht.begin();
}

void loop() {
  // Wait between measurements (2 seconds for DHT22, 1 for DHT11)
  delay(2000);
  
  // Read humidity as percentage
  float humidity = dht.readHumidity();
  
  // Read temperature as Celsius (default)
  float tempC = dht.readTemperature();
  
  // Read temperature as Fahrenheit
  float tempF = dht.readTemperature(true);
  
  // Check if any reads failed
  if (isnan(humidity) || isnan(tempC) || isnan(tempF)) {
    Serial.println("Failed to read from DHT sensor!");
    return;
  }
  
  // Calculate heat index (apparent temperature)
  float heatIndexF = dht.computeHeatIndex(tempF, humidity);
  float heatIndexC = dht.computeHeatIndex(tempC, humidity, false);
  
  // Display results in Serial Monitor
  Serial.print("Humidity: ");
  Serial.print(humidity);
  Serial.print("%\t");
  
  Serial.print("Temperature: ");
  Serial.print(tempC);
  Serial.print("°C / ");
  Serial.print(tempF);
  Serial.print("°F\t");
  
  Serial.print("Heat index: ");
  Serial.print(heatIndexC);
  Serial.print("°C / ");
  Serial.print(heatIndexF);
  Serial.println("°F");
}

Code Explanation: This example uses the DHT library to simplify communication with the sensor. The readHumidity() and readTemperature() methods handle all the complex timing, and the computeHeatIndex() function calculates the "feels like" temperature based on both temperature and humidity.

5 Code Customization Guide

To adapt this code for your specific project, modify these key sections:

• Change Sensor Type: Comment/uncomment the appropriate #define DHTTYPE line for your sensor (DHT11 or DHT22)
• Change Data Pin: Modify #define DHTPIN 2 to use a different Arduino digital pin
• Adjust Reading Delay: Change delay(2000) to delay(1000) for DHT11 or longer for energy-saving applications
• Add Output Displays: Extend the code to send data to LCD displays, web servers, or SD card loggers
• Implement Alerts: Add conditional statements to trigger actions when temperature/humidity exceed thresholds

6 Serial Monitor Output

After uploading the code to your Arduino, follow these steps to verify it's working:

1. Open Serial Monitor: In Arduino IDE, go to Tools > Serial Monitor
2. Set Baud Rate: Ensure it's set to 9600 (matches Serial.begin(9600) in code)
3. Check Output: You should see readings every 2 seconds like this:

DHTxx sensor test!
Humidity: 45.0%   Temperature: 22.5°C / 72.5°F   Heat index: 21.9°C / 71.4°F
Humidity: 44.8%   Temperature: 22.6°C / 72.7°F   Heat index: 22.0°C / 71.6°F

7 Common Issues and Solutions

If you encounter problems with your DHT sensor, follow this systematic troubleshooting approach:

8 Taking Your Project Further

Once you've mastered basic DHT sensor usage, consider these advanced enhancements:

• Multiple Sensors: Create a network of DHT sensors to monitor different locations or zones
• Wireless Connectivity: Add WiFi (ESP8266/ESP32) or Bluetooth to transmit data wirelessly
• Data Logging: Implement SD card storage or cloud uploading for long-term data analysis
• Visual Displays: Add LCD or OLED screens for standalone operation without computers
• Automated Controls: Integrate with relays to control fans, heaters, or humidifiers based on readings
• Web Interface: Create a dashboard to monitor conditions remotely via web browser