Arduino - Humidity Sensor



    Sohail Gulam


    The DHT-22 (also named as AM2302) is a digital-output, relative humidity, and temperature sensor. It uses a capacitive humidity sensor and a thermistor to measure the surrounding air, and sends a digital signal on the data pin.

    In this example, you will learn how to use this sensor with Arduino UNO. The room temperature and humidity will be printed to the serial monitor.

    #include "DHT.h"
    #define DHTPIN 2 // what digital pin we're connected to
    // Uncomment whatever type you're using!
    //#define DHTTYPE DHT11 // DHT 11
    #define DHTTYPE DHT22 // DHT 22 (AM2302), AM2321
    //#define DHTTYPE DHT21 // DHT 21 (AM2301)
    // 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.
    void setup() {
       Serial.println("DHTxx test!");
    void loop() {
       delay(2000); // Wait a few seconds between measurements
       float h = dht.readHumidity();
       // Reading temperature or humidity takes about 250 milliseconds!
       float t = dht.readTemperature();
       // Read temperature as Celsius (the default)
       float f = dht.readTemperature(true);
       // Read temperature as Fahrenheit (isFahrenheit = 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!");
       // 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");
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