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DHT11: Measuring temperature and humidity with the ESP32 in Arduino code

DHT11 sensor overview

The DHT11 sensor with its typical blue protection

The DHT11 sensor is a trendy temperature and humidity sensor in the Makers and DIY world. Its low price and ease of use have given it this success.

Warning

The fact that you can only get one measurement per second is its main drawback. It will be perfectly suitable for making a DIY IoT weather station. 🙂

Getting started with the DHT11 sensor

A higher-end model, the DHT 22, is more complete. To differentiate them, we can look at the colors of their housing: the DHT11 has blue housing while the DHT22 is white. The DHT22 is also slightly bigger. Apart from their differences, they are used in the same way. Please compare DHT11 and DHT22 sensors to learn more about the differences.

Some technical characteristics of the DHT11

The DHT11 can be directly powered by 3.3V.

DHT11 Specifications

Features

DHT11

Temperature accuracy

± 2°C

Humidity accuracy

± 5%

Temperature range

0-50 °C

Humidity range

20-90%

Sampling

1/s

Supply voltage

3-5.5V

Current consumption

~2.5mA

The performances are simple, which limits the use of the sensor. I advise you to use a sensor of the BMExxx series of the manufacturer Bosh for better measurements.

DHT11 Sensor Wiring on ESP32

The DHT 11 sensor has between 3 and 4 pins. Depending on your module on the 4-pin model, one pin is useless. Unfortunately, different pin-outs rely on the module manufacturer. Here is a summary of the other possibilities:

DHT11 variant

Different pin-outs are possible (Elegoo’s is on the left)

The numbering is done from the left when you hold the sensor facing you (the part with the grid in front of you).

Pin Wiring

DHT11 Module

ESP32

1 ( S )

GPIO17

2

3V3

3 ( - )

GND

Pin Wiring

DHT11 Module

ESP32

1

GND

2

GPIO17

3

3V3

Pin Wiring

DHT11 Module

ESP32

1

3V3

2

GPIO17

3

Ne pas connecter

4

GND

Apart from the power supply pins, the DHT11 has a single pin to transmit sensor data.

Wiring diagram for using the DHT11 module with an ESP32

If the module does not contain a pullup resistor, you must add one between 4.7kΩ (or 10kΩ ) between the pins 3V3 and the signal (GPIO17 ). You can always add one more; it won’t hurt.

Any output pin can be used. Here we use the pin GPIO17 . In the following diagrams, I use the DHT11 sensor from Elegoo; please make sure to adapt it to your model if it is slightly different. 🙂

Wiring of the DHT11 and esp32 wroom

Wiring the DHT11 with a uPesy ESP32 Wroom DevKit board

Wiring on DHT11 and esp32 wroom prototyping plate

Wiring the DHT11 with a uPesy ESP32 Wroom DevKit on a breadboard

Warning

Make sure you supply the module with 3.3V and not 5V to have a 3.3V data signal.

Measuring the temperature and humidity of the DHT11 with Arduino code

Since the DHT11 uses a proprietary protocol, it is essential to use a library to communicate easily with the sensor. It would be best if you used adafruit’s DHT Sensor library, which works properly on the ESP32 .

Here is how to install it from the Arduino IDE :

Installation of the DHT11 arduino ide library

Installation of the DHT11 library on Arduino IDE

Once the library is installed, we use the following code that retrieves the temperature and humidity of the DHT11.

#include "DHT.h"

#define DHTPIN 17
#define DHTTYPE DHT11
//DHTTYPE = DHT11, but there are also DHT22 and 21

DHT dht(DHTPIN, DHTTYPE); // constructor to declare our sensor

void setup() {
  Serial.begin(115200);
  dht.begin();
}

void loop() {
  delay(1000);
  // The DHT11 returns at most one measurement every 1s
  float h = dht.readHumidity();
  //Read the moisture content in %.
  float t = dht.readTemperature();
  //Read the temperature in degrees Celsius
  float f = dht.readTemperature(true);
  // true returns the temperature in Fahrenheit

  if (isnan(h) || isnan(t) || isnan(f)) {
    Serial.println("Failed reception");
    return;
    //Returns an error if the ESP32 does not receive any measurements
  }

  Serial.print("Humidite: ");
  Serial.print(h);
  Serial.print("%  Temperature: ");
  Serial.print(t);
  Serial.print("°C, ");
  Serial.print(f);
  Serial.println("°F");
  // Transmits the measurements received in the serial monitor
}

Note

The DHT.h at the beginning of the program includes the DHT Sensor library.

This is what you get in the console:

Reading of arduino ide console measurements

Note

You can blow on the DHT11 sensor like a cold window to clear the fog. You should see the humidity level skyrocket.

It is not possible to have more measurements per second. This sensor is not very suitable for quickly detecting a sudden temperature change.

Making asynchronous measurements with the DHT11 sensor

You will notice that the measurement is blocked: the ESP32 cannot do anything else during the measurements. An obvious solution is to replace the delay() with the function millis() in a condition if . But despite this, the exchange of data with the DHT11 will permanently be blocked: your program will be blocked by jerks

The best solution is to use a library that works with timers and interrupts so that the measurements are done in the background:

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