Arduino Temperature and humidity sensor using DHT11

 

The DHT11 sensor can measure both temp and humidity.

Introduction-

Technical Details

• 3.5 to 5v power and I/O
• 2.5mA max current use during conversion (while requesting data)
• Good for 20-80% humidity readings with 5% accuracy
• Good for 0-50°C temperature readings ±2°C accuracy
• No more than 1 Hz sampling rate (once every second)
• 4 pins with 0.1" spacing

Cost - About 1$.

Pinout

How to use-

In order to use the DHT11 Humidity and temperature sensor, we need an Arduino board.

Connection- DHT11/22 - Arduino

               VCC  -  5V

               GND  - GND 

               DATA - Pin 3(Digital Pin 3)

Note: You can connect data pin to any digital pin according to your program.

Library

You need to install dht11 library first.

Adafruit DHT-sensor-library and Adafrit-Unified-sensor-library.
This library is compatible with both Arduino and ESP8266.

To install a library -

If you got a zip file , unzip it and place in Arduino_installation_directory\libraries
OR you can just go to Arduino IDE > Click on sketch > Include Library > Manager Libraries > Search for dht >  Install DHT Sensor Library and Unified Library by Adafruit.

Coding-

Following lines will print information about Sensor (which is not useful).

  Serial.println("Temperature");
  Serial.print  ("Sensor:       "); Serial.println(sensor.name);
  Serial.print  ("Driver Ver:   "); Serial.println(sensor.version);
  Serial.print  ("Unique ID:    "); Serial.println(sensor.sensor_id);
  Serial.print  ("Max Value:    "); Serial.print(sensor.max_value); Serial.println(" *C");
  Serial.print  ("Min Value:    "); Serial.print(sensor.min_value); Serial.println(" *C");
  Serial.print  ("Resolution:   "); Serial.print(sensor.resolution); Serial.println(" *C");  
  Serial.println("------------------------------------");
  // Print humidity sensor details.
  dht.humidity().getSensor(&sensor);
  Serial.println("------------------------------------");
  Serial.println("Humidity");
  Serial.print  ("Sensor:       "); Serial.println(sensor.name);
  Serial.print  ("Driver Ver:   "); Serial.println(sensor.version);
  Serial.print  ("Unique ID:    "); Serial.println(sensor.sensor_id);
  Serial.print  ("Max Value:    "); Serial.print(sensor.max_value); Serial.println("%");
  Serial.print  ("Min Value:    "); Serial.print(sensor.min_value); Serial.println("%");
  Serial.print  ("Resolution:   "); Serial.print(sensor.resolution); Serial.println("%");  

Below are the important lines to include in the sketch.

#include <Adafruit_Sensor.h>
#include <DHT.h>
#include <DHT_U.h>

#define DHTPIN            3         // Pin to which DHT pin connected, Any pin can be used.

// Uncomment the type of sensor in use:
#define DHTTYPE           DHT11     // DHT 11 
//#define DHTTYPE           DHT22     // DHT 22 (AM2302)
//#define DHTTYPE           DHT21     // DHT 21 (AM2301)

DHT_Unified dht(DHTPIN, DHTTYPE);
void setup() {
  Serial.begin(9600); 
  dht.begin();
  sensor_t sensor;
  dht.temperature().getSensor(&sensor);
  dht.humidity().getSensor(&sensor);
}

void loop() {
  delay(2000);
  sensors_event_t event;  
  dht.temperature().getEvent(&event);
  dht.humidity().getEvent(&event);
}

Note- The data from the DHT11 must be received with atleast a delay of 1 second.

The above code must not to be changed, its bare minimum to get DHT to work .


But to get temperature and humidity, we need to add these lines in loop






Following function will check sensors for errors ( yes DHT11 has two sensors) and return 1  any error occured.

isnan(event.temperature)
isnan(event.relative_humidity)

So this can be used in if else statements.

Following will return temperature and humidity.

event.temperature
event.relative_humidity

Sample Sketch

The following code will print temperature and humidity in the serial monitor.

#include <Adafruit_Sensor.h>
#include <DHT.h>
#include <DHT_U.h>

#define DHTPIN            3         // Pin to which DHT pin connected, Any pin can be used.

// Uncomment the type of sensor in use:
#define DHTTYPE           DHT11     // DHT 11 
//#define DHTTYPE           DHT22     // DHT 22 (AM2302)
//#define DHTTYPE           DHT21     // DHT 21 (AM2301)

DHT_Unified dht(DHTPIN, DHTTYPE);
void setup() {
  Serial.begin(9600); 
  dht.begin();
  sensor_t sensor;
  dht.temperature().getSensor(&sensor);
  dht.humidity().getSensor(&sensor);
}

void loop() {
  delay(2000);
  sensors_event_t event;  
  dht.temperature().getEvent(&event);
  dht.humidity().getEvent(&event);
  
  if (isnan(event.temperature)) 
  Serial.println("Error reading temperature!");
  else
  {
    Serial.print("Temperature : ");
    Serial.print(event.temperature);
    Serial.println(" celsius");
  }
  
  if (isnan(event.relative_humidity))
  Serial.println("Error reading humidity!");
  else 
  {
    Serial.print("Humidity : ");
    Serial.print(event.relative_humidity);
    Serial.println(" %");
  }
}
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