DHT22 – Temperature and Humidity Sensor (more accurate than DHT11)

DHT22 – Temperature and Humidity Sensor (more accurate than DHT11)

The DHT22 sensor is a popular choice for measuring temperature and humidity in various applications, offering higher accuracy and a broader measurement range compared to its counterpart, the DHT11. Both sensors are commonly used in environmental monitoring systems, HVAC controls, and weather stations, but the DHT22 stands out due to its superior performance.​

Understanding the DHT22 Sensor

The DHT22, also known as the AM2302, is a low-cost digital sensor that provides accurate measurements of temperature and humidity. It operates on a simple communication protocol, making it easy to interface with microcontrollers like Arduino and Raspberry Pi.​Pixel Electric+3Phipps Electronics+3Faranux Electronics+3

Key Features of the DHT22:

These specifications make the DHT22 suitable for applications requiring precise environmental measurements.​

DHT22 vs. DHT11: A Comparative Overview

While both sensors serve the same primary function, there are notable differences between the DHT22 and DHT11:​

SpecificationDHT11DHT22
Temperature Range0-50°C with ±2°C accuracy-40 to 80°C with ±0.5°C accuracy
Humidity Range20-80% with ±5% accuracy0-100% with ±2-5% accuracy
Sampling Rate1 Hz (one reading per second)0.5 Hz (one reading every two seconds)
Size15.5 x 12 x 5.5 mm15.1 x 25 x 7.7 mm

The DHT22’s extended temperature and humidity ranges, along with its higher accuracy, make it more suitable for applications where precise environmental monitoring is crucial. However, the DHT11’s faster sampling rate and smaller size might be advantageous in projects where space is limited, and extreme accuracy is not as critical.​

How the DHT22 Sensor Works

The DHT22 sensor comprises three main components:​Flyrobo

  1. Humidity Sensing Component: This consists of two electrodes with a moisture-holding substrate between them. Changes in humidity alter the conductivity between the electrodes, which the sensor detects and converts into a digital signal.​Flyrobo
  2. Thermistor (Temperature Sensor): An NTC (Negative Temperature Coefficient) thermistor measures temperature. Its resistance decreases as the temperature rises, allowing the sensor to calculate the ambient temperature accurately.​
  3. Integrated Chip: This processes the analog signals from the humidity and temperature sensors, converting them into a digital format for transmission to a microcontroller.​

Interfacing the DHT22 with a Microcontroller

Connecting the DHT22 to a microcontroller like an Arduino is straightforward due to its single-wire communication protocol. The sensor has four pins:​Flyrobo

  1. VCC: Power supply (3.3V to 5V).​
  2. GND: Ground.​Flyrobo
  3. DATA: Serial data output.​MBK test+5Circuit Electronics+5Flyrobo+5
  4. NC: Not connected.​MBK test+4Flyrobo+4Circuit Electronics+4

Wiring Steps:

  1. Connect the VCC pin to the 5V output of the Arduino.​How To Mechatronics
  2. Connect the GND pin to the ground (GND) of the Arduino.​
  3. Connect the DATA pin to a digital input pin on the Arduino (e.g., pin 2).​
  4. Place a 10kΩ pull-up resistor between the DATA and VCC pins to ensure reliable communication.​

Programming the Arduino to Read DHT22 Data

To read data from the DHT22 sensor, you can use the DHT sensor library available in the Arduino IDE. This library simplifies the process of communicating with the sensor.​

Installation Steps:

  1. Open the Arduino IDE.​
  2. Navigate to Sketch > Include Library > Manage Libraries.​MBK test
  3. In the Library Manager, search for “DHT sensor library” by Adafruit.​
  4. Click “Install” to add the library to your IDE.​

Sample Code:

cppCopyEdit#include "DHT.h"

#define DHTPIN 2     // Digital pin connected to the DHT sensor
#define DHTTYPE DHT22   // DHT22 (AM2302)

DHT dht(DHTPIN, DHTTYPE);

void setup() {
  Serial.begin(9600);
  dht.begin();
}

void loop() {
  delay(2000);  // Wait a few seconds between measurements

  float humidity = dht.readHumidity();
  float temperature = dht.readTemperature();

  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.println(" *C");
}

This code initializes the DHT22 sensor and reads the temperature and humidity every two seconds, displaying the results on the Serial Monitor.​Flyrobo

Applications of the DHT22 Sensor

Due to its accuracy and reliability, the DHT22 sensor is used in various applications, including:​

  • Weather Stations: Monitoring local environmental conditions.​
  • HVAC Systems: Regulating heating, ventilation, and air conditioning based on real-time data.