Arduino Temperature & Humidity Sensor

This tutorial will use DHT22 sensor which has the following characterisitics:

  • Low cost
  • 3 to 5V power and I/O
  • 2.5mA max current use during conversion (while requesting data)
  • Good for 0-100% humidity readings with 2-5% accuracy
  • Good for -40 to 125°C temperature readings ±0.5°C accuracy
  • No more than 0.5 Hz sampling rate (once every 2 seconds)
  • Body size 15.1mm x 25mm x 7.7mm
  • 4 pins with 0.1″ spacing

The four pins functions are as follows:

  • VCC (3 to 5V power)
  • Data out
  • Not connected
  • Ground

You would need a small breadboard, several wires and a 10k resistor. Please connect it up this way.

  • VCC to Arduino’s 5v or 3.3v pin
  • Data out to Pin 2 or any other free pin.
  • Ground to any ground pin
  • Connect the 10k resistor between power wire and the Data out wire.

Download the DHTSensorLibrary into your Arduino IDE library folder:

upload the following example:

// 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
// 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
 
DHT dht(DHTPIN, DHTTYPE);
 
 
void setup() {
 
  Serial.begin(9600);
 
  Serial.println("DHTxx test!");
 
 
  dht.begin();
 
}
 
 
void loop() {
 
  // 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();
 
  float t = dht.readTemperature();
 
 
  // check if returns are valid, if they are NaN (not a number) then something went wrong!
 
  if (isnan(t) || isnan(h)) {
 
    Serial.println("Failed to read from DHT");
 
  } else {
 
    Serial.print("Humidity: ");
 
    Serial.print(h);
 
    Serial.print(" %\t");
 
    Serial.print("Temperature: ");
 
    Serial.print(t);
 
    Serial.println(" *C");
 
  }
 
}


This will start printing out output onto your Arduino IDE Serial Monitor once you upload it.

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