DHT 22 Digital Temperature and Humidity Sensor

The DHT22 is a basic, low-cost digital temperature and humidity sensor now available in stock at Tomson Electronics, Kochi, Kerala, India. It uses a capacitive humidity sensor and a thermistor to measure the surrounding air and spits out a digital signal on the data pin. It is very simple to use with an Arduino or Raspberry Pi but requires careful timing to grab data. The only real downside of this sensor is you can only get new data from it once every 2 seconds, so when using a library, sensor readings can be up to 2 seconds old.

Connect the first pin on the left to a 3-5V power source, the second pin to your data input pin and the rightmost pin to ground. Although it uses a single-wire to send data it is not Dallas One Wire compatible. If you want multiple sensors, each one must have its own data pin.

Compared to the DHT11, this sensor is more precise, more accurate and works in a bigger range of temperature/humidity, but it is larger and slightly more expensive.

Use the following Code to Test Your DHT 22 Sensor with Arduino

NOTE: Library is available in the Download Section

Arduino Code

// Example testing sketch for various DHT humidity/temperature sensors

#include "DHT.h"

#define DHTPIN 2 // what digital pin we're connected to

// Uncomment whatever type you're using!

#define DHTTYPE DHT22 // DHT 22 (AM2302), AM2321


// Connect pin 1 (on the left) of the sensor to +5V
// NOTE: If using a board with 3.3V logic like an Arduino Due connect pin 1
// to 3.3V instead of 5V!
// Connect pin 2 of the sensor to whatever your DHTPIN is
// Connect pin 4 (on the right) of the sensor to GROUND
// Connect a 10K resistor from pin 2 (data) to pin 1 (power) of the sensor

// Initialize DHT sensor.
// Note that older versions of this library took an optional third parameter to
// tweak the timings for faster processors. This parameter is no longer needed
// as the current DHT reading algorithm adjusts itself to work on faster procs.
DHT dht(DHTPIN, DHTTYPE);

void setup() {
Serial.begin(9600);
Serial.println("DHTxx test!");

dht.begin();
}

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

// Reading temperature or humidity takes about 250 milliseconds!
// Sensor readings may also be up to 2 seconds 'old' (its a very slow sensor)
float h = dht.readHumidity();
// Read temperature as Celsius (the default)
float t = dht.readTemperature();
// Read temperature as Fahrenheit (isFahrenheit = true)
float f = dht.readTemperature(true);

// Check if any reads failed and exit early (to try again).
if (isnan(h) || isnan(t) || isnan(f)) {
Serial.println("Failed to read from DHT sensor!");
return;
}

// Compute heat index in Fahrenheit (the default)
float hif = dht.computeHeatIndex(f, h);
// Compute heat index in Celsius (isFahreheit = false)
float hic = dht.computeHeatIndex(t, h, false);

Serial.print("Humidity: ");
Serial.print(h);
Serial.print(" %\t");
Serial.print("Temperature: ");
Serial.print(t);
Serial.print(" *C ");
Serial.print(f);
Serial.print(" *F\t");
Serial.print("Heat index: ");
Serial.print(hic);
Serial.print(" *C ");
Serial.print(hif);
Serial.println(" *F");
}