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Lesson 19: Temperature and Humidity Sensor Module (DHT11)

In this lesson, you’ll learn how to measure temperature and humidity, as well as calculate the heat index using a DHT11 sensor with an Arduino Uno. We’ll cover reading and interpreting data from the DHT11 sensor, and displaying these values along with the heat index in both Celsius and Fahrenheit on the serial monitor. This project is perfect for Arduino beginners, providing hands-on experience with sensors and data handling in a simple yet engaging way.

Required Components

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
Universal Maker Sensor Kit	94	Universal Maker Sensor Kit

You can also buy them separately from the links below.

Component Introduction	Purchase Link
Arduino UNO R3 or R4	BUY
Temperature and Humidity Sensor Module (DHT11)	BUY

Wiring

Note

The kit may contain different versions of the DHT11 module. Please confirm the wiring method according to the module you have.

module	diagram

Code

Note

To install the library, use the Arduino Library Manager and search for “DHT sensor library” and install it.

Code Analysis

Inclusion of necessary libraries and definition of constants. This part of the code includes the DHT sensor library and defines the pin number and sensor type used in this project.

Note

To install the library, use the Arduino Library Manager and search for “DHT sensor library” and install it.
```
#include <DHT.h>
#define DHTPIN 2       // Define the pin used to connect the sensor
#define DHTTYPE DHT11  // Define the sensor type
```
Creation of DHT object. Here we create a DHT object using the defined pin number and sensor type.
```
DHT dht(DHTPIN, DHTTYPE);  // Create a DHT object
```

This function is executed once when the Arduino starts. We initialize the serial communication and the DHT sensor in this function.

void setup() {
  Serial.begin(9600);
  Serial.println(F("DHT11 test!"));
  dht.begin();  // Initialize the DHT sensor
}

Main loop. The loop() function runs continuously after the setup function. Here, we read the humidity and temperature values, calculate the heat index, and print these values to the serial monitor. If the sensor read fails (returns NaN), it prints an error message.

Note

The heat index is a way to measure how hot it feels outside by combining the air temperature and the humidity. It is also called the “felt air temperature” or “apparent temperature”.

void loop() {
  delay(2000);
  float h = dht.readHumidity();
  float t = dht.readTemperature();
  float f = dht.readTemperature(true);
  if (isnan(h) || isnan(t) || isnan(f)) {
    Serial.println(F("Failed to read from DHT sensor!"));
    return;
  }
  float hif = dht.computeHeatIndex(f, h);
  float hic = dht.computeHeatIndex(t, h, false);
  Serial.print(F("Humidity: "));
  Serial.print(h);
  Serial.print(F("%  Temperature: "));
  Serial.print(t);
  Serial.print(F("°C "));
  Serial.print(f);
  Serial.print(F("°F  Heat index: "));
  Serial.print(hic);
  Serial.print(F("°C "));
  Serial.print(hif);
  Serial.println(F("°F"));
}