Monday, May 11, 2015

Arduino Nano + DHT11, Temperature & Humidity sensors

This example run on Arduino Nano, read DHT11 (Temperature & Humidity sensors), send data to PC via serial. The library adafruit/DHT-sensor-library is used to read DHT11.

The library adafruit/DHT-sensor-library is included in Arduino IDE library sources, so it's easy to add it to your project. Read the video to know how to add the library to Arduino IDE.

Once the library added, you can find a example in File -> Examples -> DHT sensor library -> DHTtester.

To make it work on Arduino Nano + DHT11, DHTtester.ino
// Example testing sketch for various DHT humidity/temperature sensors
// Written by ladyada, public domain

#include "DHT.h"

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

// Uncomment whatever type you're using!
#define DHTTYPE DHT11   // DHT 11 
//#define DHTTYPE DHT22   // DHT 22  (AM2302)
//#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 for normal 16mhz Arduino
// NOTE: For working with a faster chip, like an Arduino Due or Teensy, you
// might need to increase the threshold for cycle counts considered a 1 or 0.
// You can do this by passing a 3rd parameter for this threshold.  It's a bit
// of fiddling to find the right value, but in general the faster the CPU the
// higher the value.  The default for a 16mhz AVR is a value of 6.  For an
// Arduino Due that runs at 84mhz a value of 30 works.
// Example to initialize DHT sensor for Arduino Due:

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

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

  // 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
  float t = dht.readTemperature();
  // Read temperature as Fahrenheit
  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!");

  // Compute heat index
  // Must send in temp in Fahrenheit!
  float hi = dht.computeHeatIndex(f, h);

  Serial.print("Humidity: "); 
  Serial.print(" %\t");
  Serial.print("Temperature: "); 
  Serial.print(" *C ");
  Serial.print(" *F\t");
  Serial.print("Heat index: ");
  Serial.println(" *F");


  1. It can occur only without degrees (. Decimal)?
    Ex .: 19 C instead of 19.25C

  2. Using decimal makes no nsens as the accuracy of DHT 11 is +-.5 to +- 2 degrees

  3. please help.. i try running examples but error, error display "
    In file included from C:\Users\Last\Documents\Arduino\libraries\DHT_sensor_library\DHT_U.cpp:22:0:

    C:\Users\Last\Documents\Arduino\libraries\DHT_sensor_library\DHT_U.h:25:29: fatal error: Adafruit_Sensor.h: No such file or directory



    compilation terminated.

    Multiple libraries were found for "DHT.h"
    Used: C:\Users\Last\Documents\Arduino\libraries\DHT_sensor_library
    Not used: C:\Users\Last\Documents\Arduino\libraries\RF24Network
    exit status 1
    Error compiling for board Arduino Nano."