DHT22 - AM2302/AM2303 temperature and humidity sensor library for Arduino

This is an Arduino library for the calibrated AM2302/AM2303 digital temperature and relative humidity sensor on a DHT22 breakout PCB.

Library features

• Read 16-bit temperature (synchronous blocking)
• Read 16-bit relative humidity (synchronous blocking)

AM2302/AM2303 sensor specifications

• Voltage: 3.3 .. 5V
• Ultra-low power:
  • Typical 15uA dormancy
  • Typical 500uA measuring
• Single wire digital serial interface
• Calibrated digital signal
• Outstanding long term stability
• No additional electronic components needed
• Humidity:
  • Range: 0 .. 99.9 %RH (Relative Humidity)
  • Resolution: 0.1 %RH
  • Accuracy: +/-2 %RH (at 25 degree Celsius)
• Temperature:
  • Range: -40 .. +125 degree Celsius
  • Resolution: 0.1 degree Celsius
  • Accuracy: +/- 0.4 degree Celsius
• Minimum read interval: 2000 ms
• ~31ms to synchronous read humidity, temperature and parity data from sensor (5 Bytes)

Safety warning

According to the datasheet, the AM2302/AM2303 is a low cost consumer temperature sensor. It may not be used in safety critical applications, emergency stop devices or any other occasion that failure of AM2302/AM2303 may cause personal injury.

Hardware

Pull-up resistor DAT pin

• Connect an external 3k3..10k pull-up resistor between the DAT and VCC pins only when:
  • Using a AM2302/AM2303 sensor without a DT22 breakout PCB and the MCU IO pin has no built-in or external pull-up resistor.
• The DHT22 breakout PCB contains a 3k3 pull-up resistor between DAT and VCC.
• Please refer to the MCU datasheet or board schematic for more information about IO pin pull-up resistors.

External capacitor

• Tip: Connect a 100nF capacitor between the sensor pins VCC and GND when read errors occurs. This may stabilize the power supply.

Connection DHT22 - Arduino

DHT22	Arduino UNO / Nano / Pro Mini / Leonardo / Mega2560
GND	GND
VCC	5V (or 3.3V)
DAT	2 (DIGITAL pin)

Connection DHT22 - ESP8266

Some ESP8266 boards uses Arduino pin 2 -> GPIO4 which is D4 text on the board. Make sure you're using the right pin.

DHT22	ESP8266 / WeMos D1 R2 / ESP12E / NodeMCU
GND	GND
VCC	3.3V
DAT	D2

Connection DHT22 - WeMos LOLIN32

WeMos LOLIN32 requires an additional 100nF capacitor over the GND - VCC pins to prevent parity errors.

Use pin 0 to prevent flash problems.

DHT22	WeMos Lolin32
GND	GND
VCC	3.3V
DAT	0

Other MCU's may work, but are not tested.

Examples

Arduino IDE | Examples | Erriez DHT22 Temperature & Humidity:

• DHT22

Documentation

• Doxygen online HTML
• Doxygen PDF
• AM2303 datasheet
• DHT22 datasheet

Usage

Initialization

#include <ErriezDHT22.h>

// Connect DTH22 DAT pin to Arduino board

// Arduino DIGITAL pin
#define DHT22_PIN      2
// Some ESP8266 boards uses D2 instead of 2
// #define DHT22_PIN   D2
// LOLIN32 uses another pin
// #define DHT22_PIN   0
  
DHT22 sensor = DHT22(DHT22_PIN);
  
void setup()
{
    // Initialize serial port
    Serial.begin(115200);
    Serial.println(F("DHT22 temperature and humidity sensor example\n"));
    
    // Initialize sensor
    sensor.begin();
}

Read temperature and humidity

void loop()
{
    // Check minimum interval of 2000 ms between sensor reads
    if (sensor.available()) {
        // Read temperature from sensor
        int16_t temperature = sensor.readTemperature();
  
        // Read humidity from sensor
        int16_t humidity = sensor.readHumidity();
  
        if (temperature == ~0) {
            // Print error (Check hardware connection)
            Serial.print(F("Temperature: Error"));
        } else {
            // Print temperature
            Serial.print(F("Temperature: "));
            Serial.print(temperature / 10);
            Serial.print(F("."));
            Serial.print(temperature % 10);
            Serial.println(F(" *C"));
        }
  
        if (humidity == ~0) {
            // Print error (Check hardware connection)
            Serial.print(F("Humidity: Error"));
        } else {
            // Print humidity
            Serial.print(F("Humidity: "));
            Serial.print(humidity / 10);
            Serial.print(F("."));
            Serial.print(humidity % 10);
            Serial.println(F(" %"));
        }
        
        Serial.println();
      }
}

Serial output

DHT22 temperature and humidity sensor example
  
Temperature: 17.7 *C
Humidity: 41.0 %
  
Temperature: 17.8 *C
Humidity: 41.1 %
  
...

Library dependencies

• None

Library installation

Please refer to the Wiki page.

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