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)
• Configurable number of read retries when a read error occurs (default is 1 read + 2 retries)
• Long time duration example
• Temperature and humidity average with a configurable number of samples to remove jitter

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.

Board - DHT22 pins	VCC	GND	DAT
Arduino UNO / Nano / Micro (ATMega328 boards)	5V (or 3V3)	GND	2 (DIGITAL pin)
Arduino Leonardo	5V (or 3V3)	GND	2 (DIGITAL pin)
Arduino Mega2560	5V (or 3V3)	GND	2 (DIGITAL pin)
Arduino DUE (ATSAM3X8E)	3V3	GND	2 (DIGITAL pin)
ESP8266 (ESP12E / WeMos D1 R2 / NodeMCU v2 or v3)	3V3	GND	GPIO4 (D2)
ESP32 (WeMos Lolin32 OLED / WeMos LOLIN D32)	3V3	GND	GPIO4

Notes:

• GPIO4 uses sketch pin number 4 and is labeled as D2 on some WeMos ESP8266 boards.
• Other MCU's may work, but are not tested.

Examples

Arduino IDE | Examples | Erriez DHT22 Temperature & Humidity:

• DHT22 Getting started example.
• DHT22Average Calculate average temperature and humidity.
• DHT22DurationTest Test reliability connection.
• DHT22Logging Write temperature and humidity every 10 minutes to .CSV file on SD-card with DS3231 RTC.
• DHT22LoggingAVR LowPower SD-card logging for AVR targets only. Arduino Pro or Pro Mini at 8MHz is recommended.
• DHT22LowPower LowPower AVR targets only. Arduino Pro or Pro Mini at 8MHz is recommended.

Documentation

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

Usage

Initialization

#include <ErriezDHT22.h>

// Connect DTH22 DAT pin to Arduino board

// Connect DTH22 DAT pin to Arduino DIGITAL pin
#if defined(ARDUINO_ARCH_AVR) || defined(ARDUINO_SAM_DUE)
#define DHT22_PIN      2
#elif defined(ESP8266) || defined(ESP32)
#define DHT22_PIN      4 // GPIO4 (Labeled as D2 on some ESP8266 boards)
#else
#error "May work, but not tested on this target"
#endif
  
DHT22 dht22 = DHT22(DHT22_PIN);
  
void setup()
{
    // Initialize serial port
    Serial.begin(115200);
    Serial.println(F("DHT22 temperature and humidity sensor example\n"));
    
    // Initialize sensor
    dht22.begin();
}

Read temperature and humidity

void loop()
{
    // Check minimum interval of 2000 ms between sensor reads
    if (dht22.available()) {
        // Read temperature from sensor
        int16_t temperature = dht22.readTemperature();
  
        // Read humidity from sensor
        int16_t humidity = dht22.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

• LowPower library for DHT22LowPower.ino.

Library installation

Please refer to the Wiki page.

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