Temperature and Humidity Sensor

In this project, you'll learn how to connect and control the DHT11 temperature and humidity sensor with the Arduino.

Parts needed:
  • Arduino
  • Temperature and humidity sensor DHT11
  • Wires
  • Breadboard

  • You also need to download the DHT library which contains all of the functions for interfacing with the DHT11 temperature sensor.
DHT11 temperature and humidity sensor      DHT11 temperature and humidity sensor     
1 Making the connections

The DHT11 has either three connections: +, Out and –
    or four connections: + (pin 1), Out (pin 2), NC (pin 3), and – (pin 4)
  • Connect the + (pin 1) to 5V on the Arduino.
  • Connect the Out (pin 2) to pin 2 on the Arduino.
  • Connect the – (pin 4) to GND on the Arduino.
2 Download the DHT library.
3 Install the DHT library by selecting Sketch from the Arduino IDE menu
  • then select Import Library or Include Library
  • then select Add Library or Add .ZIP Library
Locate and select the DHT.zip file that you just downloaded in step 2. It should be in the Download folder.

Click the Open button

(Refer to this document for more information on how to install a library if you run into problems.)
4 Create a new program by selecting File from the menu
  • then select Examples
  • then select DHT
  • then select DHTtester
You will see this code.

The #include "DHT.h" line includes the DHT temperature library code.

Uncomment the #define DHTTYPE DHT11 line by removing the two slashes in front of it.
Comment out the #define DHTTYPE DHT22 line by adding two slashes in front of it.
// Example testing sketch for various DHT humidity/temperature sensors
// Written by ladyada, public domain

#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.
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");
}
3 Upload the program, then open up the serial monitor. You should see the temperature and humidity displayed on the monitor.