ESP32 Tutorial 28/55 - DHT11 Temperature Sensor with LCD | SunFounder's ESP32 IoT Learning kit

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ESP32 Tutorial 28/55 - DHT11 Temperature Sensor with LCD | SunFounder's ESP32 IoT Learning kit

In this tutorial, we will explore how to interface the DHT11 temperature and humidity sensor with the ESP32 microcontroller. Using this setup, we will measure the ambient temperature and humidity, displaying the results on both the serial monitor and an LCD screen. Additionally, we will implement a buzzer that activates when the temperature exceeds a certain threshold.

This project not only demonstrates the use of the DHT11 sensor but also showcases the versatility of the ESP32, which includes built-in Wi-Fi and Bluetooth capabilities. By the end of this tutorial, you will have a working setup that continuously monitors environmental conditions and provides real-time feedback.

For a visual guide, check out the video accompanying this tutorial (in video at 00:00). Let's dive in!

Hardware Explained

The main components used in this project are the ESP32 microcontroller, the DHT11 sensor, and an LCD display. The ESP32 will serve as the brain of the operation, processing data from the DHT11 sensor and controlling the LCD output.

The DHT11 sensor measures humidity and temperature, providing readings through a single data line. It requires a power supply of 3.3V to 5.5V and has a low current consumption, making it suitable for battery-powered applications. The LCD will display the temperature and humidity values in real-time.

Datasheet Details

Manufacturer	GROVE
Part number	DHT11
Logic/IO voltage	3.3 – 5.5 V
Supply voltage	3.3 V
Output current (per channel)	0.5 mA typ.
Peak current (per channel)	2.5 mA max.
PWM frequency guidance	N/A
Input logic thresholds	0.3 VCC (low), 0.7 VCC (high)
Voltage drop / R_DS(on) / saturation	Not applicable
Thermal limits	0°C to 60°C
Package	DIP-4
Notes / variants	Resolution: 1°C / 1% RH

Use a pull-up resistor (5 kΩ recommended) on the data line.
Keep sensor wires short (less than 20 m) to ensure accurate readings.
Power the DHT11 with 3.3V for optimal performance.
Sampling period should not be less than 1 second.
Check wiring connections if readings fail (e.g., not connected, incorrect pin).

Wiring Instructions

To wire the DHT11 sensor to the ESP32, start by connecting the VCC pin of the DHT11 (the leftmost pin) to the 3.3V output of the ESP32. Next, connect the ground pin (the fourth pin) to a ground (GND) pin on the ESP32. The data pin (the second pin) should be connected to GPIO pin 14 on the ESP32.

For the LCD, connect the VCC pin to the 5V output of the ESP32. The ground pin should be connected to a ground pin on the ESP32. The SDA and SCL pins of the LCD should be connected to GPIO pins 21 and 22, respectively. Ensure all connections are secure to avoid any issues while reading data.

Code Examples & Walkthrough

In the first part of the code, we initialize the DHT sensor and set the pin number with #define DHTPIN 14. This identifier allows us to easily reference the pin connected to the DHT11 data line throughout the code.

#include "DHT.h"

#define DHTPIN 14  // Set the pin connected to the DHT11 data pin
#define DHTTYPE DHT11 // DHT 11 
DHT dht(DHTPIN, DHTTYPE);

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

In the setup() function, we initialize serial communication for debugging and begin the DHT sensor. The main loop includes a delay of 2 seconds to ensure we do not overwhelm the sensor with requests.

Next, we read the humidity and temperature values using float humidity = dht.readHumidity(); and float temperature = dht.readTemperature();. These identifiers store the measured values for later use.

void loop() {
  delay(2000);
  float humidity = dht.readHumidity();
  float temperature = dht.readTemperature();
}

Finally, we check for any read errors and print the values to the serial monitor using Serial.print(). This allows us to observe the readings in real-time.

if (isnan(humidity) || isnan(temperature)) {
  Serial.println("Failed to read from DHT sensor!");
  return;
}
Serial.print("Humidity: "); 
Serial.print(humidity);
Serial.print(" %\t");
Serial.print("Temperature: "); 
Serial.print(temperature);
Serial.println(" *C");

In the LCD code, we initialize the LCD and display the temperature and humidity on the screen using the lcd.print() function. This provides a visual representation of the data collected by the DHT11 sensor.

Demonstration / What to Expect

Once everything is wired correctly and the code is uploaded to the ESP32, you should see the temperature and humidity readings displayed on the serial monitor and the LCD screen. If the temperature exceeds 30°C, the buzzer will activate, providing an audible alert.

Be cautious of reversed connections and ensure the sensor is not exposed to extreme conditions, as it can affect the readings. You might need to adjust the threshold for the buzzer depending on your requirements (in video at 15:30).