ESP32 Beginner Course #8: Temperature and Humidity Sensor with DHT11 or DHT22

Introduction

In this lesson, the ESP32 will read real environmental data.

We will measure temperature and humidity using a DHT11 or DHT22 sensor. This is a common beginner project, but it also introduces an important idea: many sensors do not simply output an analog voltage. Instead, they communicate using a digital signal and a library handles the timing.

This is the first step toward weather stations, smart rooms, greenhouses, and IoT monitoring systems.

What you will learn

By the end of this tutorial, you should understand:

• What temperature and humidity sensors measure
• Difference between analog sensors and digital sensors
• How to wire a DHT11 or DHT22 sensor
• How to install an Arduino library
• How to read temperature and humidity
• How to detect failed readings
• How this project connects to IoT dashboards

DHT11 vs DHT22

Both sensors measure temperature and relative humidity.

The DHT11 is usually cheaper and less accurate. The DHT22 usually has a wider measurement range and better accuracy.

For beginner code, the wiring and library usage are almost the same. The main difference is the sensor type you select in code.

#define DHTTYPE DHT11

or:

#define DHTTYPE DHT22

Digital sensor concept

In the LDR and potentiometer lessons, the ESP32 measured voltage with the ADC.

A DHT sensor works differently. It measures temperature and humidity internally, then sends the result as digital data on its DATA pin.

The timing of that signal is specific, so we use a library instead of manually reading the pin.

Hardware required

• ESP32 DevKit
• DHT11 or DHT22 sensor module
• Breadboard
• Jumper wires
• USB cable

If you are using a bare DHT sensor instead of a module, add a 10k pull-up resistor between VCC and DATA.

Wiring

Connect the sensor:

DHT VCC  -> 3.3V
DHT GND  -> GND
DHT DATA -> GPIO4

Many DHT modules already include the required pull-up resistor. Bare sensors usually need an external pull-up resistor.

Install the library

In Arduino IDE:

1. Open Library Manager
2. Search for DHT sensor library
3. Install the Adafruit DHT sensor library
4. Install dependencies if Arduino IDE asks

Libraries are useful because they hide low-level timing details and give us simple functions like readTemperature() and readHumidity().

Source code

#include "DHT.h"

#define DHTPIN 4
#define DHTTYPE DHT11

DHT dht(DHTPIN, DHTTYPE);

void setup()
{
    Serial.begin(115200);
    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");
        delay(2000);
        return;
    }

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

    delay(2000);
}

If you are using a DHT22, change:

#define DHTTYPE DHT11

to:

#define DHTTYPE DHT22

Code explanation

First, include the library:

#include "DHT.h"

Then define the data pin and sensor type:

#define DHTPIN 4
#define DHTTYPE DHT11

Create the sensor object:

DHT dht(DHTPIN, DHTTYPE);

Start the sensor in setup():

dht.begin();

Read values in loop():

float humidity = dht.readHumidity();
float temperature = dht.readTemperature();

The DHT library returns NaN, or “not a number”, when the reading fails. That is why we check:

if (isnan(humidity) || isnan(temperature))

This prevents the program from treating invalid data as real sensor data.

Test the sensor

Open Serial Monitor at 115200 baud.

You should see temperature and humidity values every two seconds.

If you place your hand near the sensor, the temperature or humidity may change slightly. Avoid heating the sensor strongly or breathing directly on it for a long time, because the readings may become slow to recover.

Common mistakes

If the reading fails:

• Check VCC and GND
• Check that the data pin matches the code
• Confirm the selected sensor type is correct
• Add a pull-up resistor if using a bare sensor
• Do not read the sensor too quickly

DHT sensors are slow compared with many other sensors. A two-second delay is a reasonable beginner value.

Real engineering use cases

Temperature and humidity sensing is used in:

• Weather stations
• Smart room monitors
• Server room monitoring
• Greenhouses
• Storage rooms
• HVAC systems
• IoT dashboards

The value of this project becomes much larger when combined with WiFi, displays, logging, and alerts.

Engineering challenge

Add a warning condition:

• If temperature is above a chosen limit, print Temperature warning
• If humidity is above a chosen limit, print Humidity warning

This is the first step toward monitoring and alert systems.

Next lesson

Next, we will connect the ESP32 to WiFi. Once the board is on the network, sensor projects can become web dashboards, IoT devices, and remote monitoring systems.