Humidity and temperature (DHT11/DHT22) in Arduino - Mini Project: Build & Apply

Humidity and temperature (DHT11/DHT22)

📖 Scenario: You want to measure the temperature and humidity in your room using a DHT11 or DHT22 sensor connected to an Arduino board. This sensor gives you two values: how warm the room is (temperature) and how much moisture is in the air (humidity).

🎯 Goal: Build a simple Arduino program that reads temperature and humidity from the DHT sensor and prints these values to the Serial Monitor.

📋 What You'll Learn

Use the DHT sensor library to read data from the sensor

Set up the sensor on a specific Arduino pin

Read temperature and humidity values from the sensor

Print the temperature and humidity values to the Serial Monitor

💡 Why This Matters

🌍 Real World

Measuring temperature and humidity is useful for weather stations, home automation, and plant care systems.

💼 Career

Understanding how to read sensor data and display it is a key skill for embedded systems and IoT device programming.

1

Set up the DHT sensor and include the library

Include the DHT.h library at the top of your sketch. Create a DHT object called dht using pin 2 and sensor type DHT11. Also, start the Serial communication at 9600 baud in the setup() function.

Arduino

# Include the DHT library and create the dht object
// Your code here

void setup() {
  // Start serial communication
  // Your code here
}

void loop() {
  // Your code here
}

Hint

Use #include <DHT.h> to include the library. Define DHTPIN as 2 and DHTTYPE as DHT11. Create the dht object with these. In setup(), start serial with Serial.begin(9600); and call dht.begin();.

2

Create variables to store humidity and temperature

Inside the loop() function, create two float variables called humidity and temperature. Use dht.readHumidity() to set humidity and dht.readTemperature() to set temperature.

Arduino

#include 

#define DHTPIN 2
#define DHTTYPE DHT11

DHT dht(DHTPIN, DHTTYPE);

void setup() {
  Serial.begin(9600);
  dht.begin();
}

void loop() {
  // Create float variables humidity and temperature
  // Your code here
}

Hint

Use float humidity = dht.readHumidity(); and float temperature = dht.readTemperature(); inside loop().

3

Check if readings are valid and print them

Add an if statement to check if humidity or temperature is NaN using isnan(). If either is NaN, print "Failed to read from DHT sensor!" and return from loop(). Otherwise, print "Humidity: " followed by humidity and " %", then print "Temperature: " followed by temperature and " *C". Add a delay of 2000 milliseconds at the end.

Arduino

#include 

#define DHTPIN 2
#define DHTTYPE DHT11

DHT dht(DHTPIN, DHTTYPE);

void setup() {
  Serial.begin(9600);
  dht.begin();
}

void loop() {
  float humidity = dht.readHumidity();
  float temperature = dht.readTemperature();
  // Check if readings are valid and print results
  // Your code here
}

Hint

Use if (isnan(humidity) || isnan(temperature)) to check for errors. Print the error message and return; if true. Otherwise, print humidity and temperature with labels and units. Use delay(2000); to wait 2 seconds before next reading.

4

Print the final output to Serial Monitor

Make sure your program prints the humidity and temperature readings every 2 seconds to the Serial Monitor in this exact format (replace numbers with actual readings):
Humidity: 45.00 %
Temperature: 23.00 *C
If the sensor fails, it should print:
Failed to read from DHT sensor!

Arduino

#include 

#define DHTPIN 2
#define DHTTYPE DHT11

DHT dht(DHTPIN, DHTTYPE);

void setup() {
  Serial.begin(9600);
  dht.begin();
}

void loop() {
  float humidity = dht.readHumidity();
  float temperature = dht.readTemperature();

  if (isnan(humidity) || isnan(temperature)) {
    Serial.println("Failed to read from DHT sensor!");
    return;
  }

  Serial.print("Humidity: ");
  Serial.print(humidity);
  Serial.println(" %");

  Serial.print("Temperature: ");
  Serial.print(temperature);
  Serial.println(" *C");

  delay(2000);

  // Your code here
}

Hint

Run your program and open the Serial Monitor at 9600 baud. You should see humidity and temperature printed every 2 seconds. If the sensor fails, the error message appears.