The DHT22 (also known as AM2302) is a digital sensor that measures temperature and humidity accurately. It’s commonly used in IoT projects, weather stations, and environmental monitoring systems.
 
Specifications
 
Temperature range: -40°C to +80°C (±0.5°C accuracy)
Humidity range: 0% to 100% RH (±2–5% accuracy)
Operating voltage: 3.3V – 6V
Output: Digital (single-wire communication)
Sampling rate: 0.5 Hz (one reading every 2 seconds)
 
Pin Configuration
 
Pin
Function
1
VCC (3.3V or 5V)
2
Data (to microcontroller)
3
NC (Not Connected)
4
GND
(Sometimes sensors come with only 3 pins: VCC, Data, GND)
 
Wiring with NodeMCU
 
DHT22 → NodeMCU
VCC → 3.3V
GND → GND
DATA → D4 (GPIO2) (with a 10k pull-up resistor to VCC)
 
Code for NodeMCU
First, install the DHT sensor library from Arduino Library Manager:
Adafruit Unified Sensor
DHT sensor library by Adafruit
 
#include "DHT.h"
// Define DHT type and pin
#define DHTPIN D4      // Data pin connected to D4
#define DHTTYPE DHT22  // Sensor type DHT22
DHT dht(DHTPIN, DHTTYPE);
void setup() {
  Serial.begin(115200);
  Serial.println("DHT22 Sensor Reading");
  dht.begin();
}
void loop() {
  float humidity = dht.readHumidity();
  float temperature = dht.readTemperature(); // Celsius
 
  // Check if any readings failed
  if (isnan(humidity) || isnan(temperature)) {
    Serial.println("Failed to read from DHT sensor!");
    return;
  }
  Serial.print("Temperature: ");
  Serial.print(temperature);
  Serial.print(" °C | Humidity: ");
  Serial.print(humidity);
  Serial.println(" %");
  delay(2000); // Update every 2 seconds
}
Applications
Smart Agriculture
Weather Stations
IoT-based Home Automation
Greenhouse Monitoring