Introduction

The DHT11 and DHT22 are widely used sensors to measure temperature and humidity.

• DHT11 → Cheaper, less accurate, works between 0–50°C, 20–80% RH.
• DHT22 → More accurate, wider range: -40–80°C, 0–100% RH.

In this tutorial, you’ll learn how to:

1. Connect DHT11/DHT22 with ESP8266
2. Read temperature and humidity values
3. Print data on the Serial Monitor

Introduction

The DHT11 and DHT22 are widely used sensors to measure temperature and humidity.

• DHT11 → Cheaper, less accurate, works between 0–50°C, 20–80% RH.
• DHT22 → More accurate, wider range: -40–80°C, 0–100% RH.

In this tutorial, you’ll learn how to:

DHT11 vs DHT22 Comparison

Feature	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	±2–3% RH
Sampling Rate	1 reading per second (1 Hz)	0.5 reading per second (0.5 Hz)
Resolution	8-bit	16-bit
Operating Voltage	3.3V – 5V	3.3V – 6V
Max Current	2.5 mA	2.5 mA
Data Format	Single-wire digital signal	Single-wire digital signal
Cost	Cheaper (low-cost sensor)	More expensive (higher accuracy)
Best Use Cases	Basic DIY projects, beginners	Weather stations, IoT, precision apps

Components Required

• ESP8266 board (NodeMCU / Wemos D1 Mini)
• DHT11 or DHT22 sensor module
• Jumper wires and breadboard

Circuit Diagram

Connections (using D1 for data):

• VCC → 3.3V
• GND → GND
• DATA → D1

👉 Some DHT modules have a built-in resistor; if not, use a 10kΩ pull-up resistor between DATA and VCC.

Installing the DHT Library

1. Open Arduino IDE → Go to Sketch > Include Library > Manage Libraries.
2. Search for “DHT sensor library” by Adafruit and install it.
3. Also install “Adafruit Unified Sensor” library.

DHT11 / DHT22 with ESP8266

#include "DHT.h"

#define DHTPIN D1      // Pin where DHT is connected
#define DHTTYPE DHT22  // Change to DHT11 if using DHT11

DHT dht(DHTPIN, DHTTYPE);

void setup() {
  Serial.begin(115200);
  dht.begin();
  Serial.println("DHT Sensor Test");
}

void loop() {
  float humidity = dht.readHumidity();
  float temperature = dht.readTemperature(); // Celsius
  float temperatureF = dht.readTemperature(true); // Fahrenheit

  if (isnan(humidity) || isnan(temperature)) {
    Serial.println("Failed to read from DHT sensor!");
    return;
  }

  Serial.print("Humidity: ");
  Serial.print(humidity);
  Serial.print(" %\t");

  Serial.print("Temperature: ");
  Serial.print(temperature);
  Serial.print(" °C  ");
  Serial.print(temperatureF);
  Serial.println(" °F");

  delay(2000); // Read every 2 seconds
}

Step-by-Step Code Explanation

1. #include "DHT.h" → Includes Adafruit’s DHT library.
2. #define DHTPIN D4 → Defines GPIO pin where sensor is connected.
3. #define DHTTYPE DHT22 → Defines sensor type (change to DHT11 if using DHT11).
4. DHT dht(DHTPIN, DHTTYPE); → Creates sensor object.
5. dht.begin(); → Initializes sensor.
6. float humidity = dht.readHumidity(); → Reads humidity in %.
7. float temperature = dht.readTemperature(); → Reads temperature in °C.
8. float temperatureF = dht.readTemperature(true); → Reads in °F.
9. isnan() check ensures values are valid.
10. Results are printed every 2 seconds.

Output on Serial Monitor

Humidity: 55.2 %   Temperature: 27.3 °C  81.1 °F
Humidity: 54.8 %   Temperature: 27.5 °C  81.5 °F

Real-Life Applications

• Smart Home Automation (monitor indoor air quality)
• Weather Stations
• Greenhouse Monitoring
• IoT Cloud Dashboards (send data to ThingSpeak, Blynk, or MQTT)

Troubleshooting

• If readings show nan (Not a Number) → check wiring and resistor.
• Use short wires; DHT sensors are sensitive to noise.
• Try slowing down reading frequency (minimum 2 seconds delay).

Conclusion

You’ve learned how to:
✅ Connect DHT11/DHT22 with ESP8266
✅ Read temperature and humidity values
✅ Print results in Serial Monitor

This project is the foundation for IoT weather and smart agriculture projects 🚀.