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

Build Status

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

DHT22 temperature and humidity sensor

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

Schematic DHT22 and Arduino UNO

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

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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