DHT11 & DHT22 Sensors - Elegets Learn

DHT Series Overview

DHT sensors are basic, low-cost digital temperature and humidity sensors that use a capacitive humidity sensor and a thermistor to measure surrounding conditions.

Digital Output: Single-wire serial interface
Low Power: 3-5V DC power supply
Integrated Sensing: Measures both temperature and humidity
Pre-calibrated: Factory calibrated for ease of use
Long-term Stability: Reliable over extended periods

Cost Effective: Very affordable compared to alternatives
Easy to Use: Simple digital interface
Good for Prototyping: Quick integration into projects
Wide Availability: Commonly stocked by electronics suppliers
Arduino Compatible: Well-supported by libraries

Weather Stations: Home environmental monitoring
HVAC Systems: Climate control feedback
Agricultural Monitoring: Greenhouse conditions
Home Automation: Smart thermostats
Industrial Applications: Equipment monitoring

DHT11 vs DHT22 Comparison

Parameter	DHT11	DHT22 (AM2302)
Temperature Range	0°C to 50°C	-40°C to 80°C
Temperature Accuracy	±2°C	±0.5°C
Humidity Range	20% to 80% RH	0% to 100% RH
Humidity Accuracy	±5% RH	±2% RH
Sampling Rate	1Hz (1 reading per second)	0.5Hz (1 reading every 2 seconds)
Power Supply	3-5.5V DC	3-6V DC
Current Consumption	0.5mA (measuring), 60μA (standby)	1.5mA (measuring), 40μA (standby)
Price	$1-$3	$4-$10

When to Choose Which Sensor

Choose DHT11 When:

Basic temperature/humidity monitoring is sufficient
Project budget is very tight
Measuring within normal room conditions (not extreme environments)
Higher sampling rate is needed

Choose DHT22 When:

Higher accuracy is required
Measuring in extreme temperatures (below 0°C or above 50°C)
Measuring very low or very high humidity levels
Project can accommodate the higher cost

Pinout and Wiring

DHT11 Pinout

VCC (3-5V): Power supply
DATA: Serial data output
NC: Not connected
GND: Ground

DHT22 Pinout

VCC (3-6V): Power supply
DATA: Serial data output
NC: Not connected
GND: Ground

Typical Wiring Diagram

Important Wiring Notes

Pull-up Resistor: 4.7KΩ-10KΩ between DATA and VCC (some modules include this)
Power Supply: Use stable power source - voltage fluctuations can cause errors
Cable Length: Keep cables short (<20cm) or use shielded cable for longer runs
Placement: Avoid placing near heat sources or in direct sunlight

DHT Sensor Libraries

Popular Libraries

DHT Sensor Library

Standard library for Arduino by Adafruit

Arduino Simple API Supports DHT11/22

GitHub

Adafruit_CircuitPython_DHT

CircuitPython library for DHT sensors

CircuitPython Raspberry Pi Python API

GitHub

SimpleDHT

Alternative Arduino library

Arduino Minimalist No dependencies

GitHub

Adafruit DHT Library Functions

// Library initialization
DHT dht(DHTPIN, DHTTYPE); // Create DHT object

// In setup():
dht.begin(); // Initialize sensor

// Reading values:
float h = dht.readHumidity();      // Read humidity (%RH)
float t = dht.readTemperature();   // Read temp in Celsius
float f = dht.readTemperature(true); // Read temp in Fahrenheit
float hif = dht.computeHeatIndex(f, h); // Compute heat index

// Error checking:
if (isnan(h) || isnan(t)) {
    Serial.println("Failed to read from DHT sensor!");
    return;
}

Library Installation

// Arduino IDE:
1. Sketch > Include Library > Manage Libraries
2. Search for "DHT sensor library"
3. Install "DHT sensor library by Adafruit"

// PlatformIO:
1. Open platformio.ini
2. Add dependency:
lib_deps = adafruit/DHT sensor library@^1.4.4

// Manual installation:
1. Download ZIP from GitHub
2. Sketch > Include Library > Add .ZIP Library
3. Select downloaded file

Code Examples

Basic Arduino Example

// Basic DHT11/DHT22 Example
#include <DHT.h>

#define DHTPIN 2      // Digital pin connected
#define DHTTYPE DHT22 // DHT 22 (AM2302)

DHT dht(DHTPIN, DHTTYPE);

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

void loop() {
    delay(2000); // Wait between measurements
    
    float h = dht.readHumidity();
    float t = dht.readTemperature();
    
    if (isnan(h) || isnan(t)) {
        Serial.println("Failed to read from DHT sensor!");
        return;
    }
    
    Serial.print("Humidity: ");
    Serial.print(h);
    Serial.print("%\tTemperature: ");
    Serial.print(t);
    Serial.println("°C");
}

ESP8266/ESP32 Example with WiFi

// ESP8266/ESP32 DHT Web Server
#include <WiFi.h>
#include <DHT.h>

#define DHTPIN 4
#define DHTTYPE DHT22

const char* ssid = "YOUR_SSID";
const char* password = "YOUR_PASSWORD";

DHT dht(DHTPIN, DHTTYPE);
WiFiServer server(80);

void setup() {
    Serial.begin(115200);
    dht.begin();
    
    WiFi.begin(ssid, password);
    while (WiFi.status() != WL_CONNECTED) {
        delay(500);
        Serial.print(".");
    }
    
    server.begin();
    Serial.println("Server started");
    Serial.println(WiFi.localIP());
}

void loop() {
    float h = dht.readHumidity();
    float t = dht.readTemperature();
    
    WiFiClient client = server.available();
    if (client) {
        String html = "<html><body>";
        html += "<h1>ESP DHT Server</h1>";
        html += "<p>Temperature: " + String(t) + "°C</p>";
        html += "<p>Humidity: " + String(h) + "%</p>";
        html += "</body></html>";
        
        client.println("HTTP/1.1 200 OK");
        client.println("Content-Type: text/html");
        client.println();
        client.println(html);
        client.stop();
    }
}

Raspberry Pi Python Example

# Raspberry Pi DHT22 Example
import Adafruit_DHT
import time

# Set sensor type and pin
DHT_SENSOR = Adafruit_DHT.DHT22
DHT_PIN = 4

while True:
    humidity, temperature = Adafruit_DHT.read_retry(DHT_SENSOR, DHT_PIN)
    
    if humidity is not None and temperature is not None:
        print(f"Temp={temperature:.1f}°C Humidity={humidity:.1f}%")
    else:
        print("Sensor failure. Check wiring.")
    
    time.sleep(3)

Controller Integration

Arduino Integration

Install DHT library via Library Manager
Connect sensor to 5V, GND, and a digital pin
Add 4.7KΩ-10KΩ pull-up resistor between DATA and VCC
Use the basic example code provided earlier
Add 2-second delays between readings

ESP8266/ESP32 Integration

Same wiring as Arduino (3.3V works despite 5V recommendation)
For battery operation, use deep sleep between readings
Consider using WiFiManager for easy WiFi configuration
For MQTT projects, use PubSubClient to send data to broker

Raspberry Pi Integration

Install required packages: sudo apt-get install python3-pip
Install library: sudo pip3 install Adafruit_DHT
Connect sensor to 3.3V (Pin 1), GND (Pin 6), and GPIO4 (Pin 7)
Use the Python example provided earlier
For headless operation, log data to file or database

Common Issues and Solutions

Issue	Possible Cause	Solution
Failed to read	Loose connection, no pull-up resistor	Check wiring, add 4.7KΩ resistor
NaN values	Timing issues, power fluctuations	Add delay between reads, use stable power
Incorrect values	Sensor placed near heat source	Relocate sensor, add ventilation
Sensor not responding	Wrong pin specified, damaged sensor	Double-check pin, try another sensor