DHT11 Temperature & Humidity Sensor

Arduino Workshop

What is the DHT11 Sensor?

The DHT11 is a basic, low-cost digital temperature and humidity sensor. It's perfect for beginners learning about environmental sensing with Arduino.

Key Features:

Measures temperature: 0-50°C (±2°C accuracy)
Measures humidity: 20-90% RH (±5% accuracy)
Digital output - easy to read!
Single wire communication protocol
Low cost and widely available

How Does DHT11 Work?

Inside the sensor:

Humidity Sensing: Uses a moisture-holding substrate between two electrodes. As humidity changes, conductivity between electrodes changes.
Temperature Sensing: Contains a thermistor (temperature-sensitive resistor) that changes resistance with temperature.
Digital Conversion: A built-in chip converts analog readings to digital signals and sends them to Arduino.

The sensor communicates using a proprietary single-wire protocol, sending 40 bits of data (humidity + temperature + checksum).

DHT11 Pin Configuration

The DHT11 sensor has 3 or 4 pins (depending on the module):

DATA: Digital signal output (denoted by s)
VCC: Power supply (3-5V)
GND: Ground (denoted by -)

Wiring DHT11 to Arduino

Connection Steps:

Connect DHT11 VCC to Arduino 5V
Connect DHT11 GND to Arduino GND
Connect DHT11 DATA to Arduino Digital Pin 2

Safety Check:

Double-check all connections before powering on
Ensure VCC and GND are not reversed
Make sure connections are secure

Installing the DHT Library

To communicate with the DHT11, we need to install a library that handles the complex timing protocol.

Installation Steps:

Open Arduino IDE
Go to Sketch → Include Library → Manage Libraries
Search for "DHT sensor library" by Adafruit
Click Install
Also install "Adafruit Unified Sensor" (dependency)

Once installed, you can include it in your sketch with: #include <DHT.h>

Basic Code Setup

First, we include the library and define our sensor configuration.

Key elements:

Include DHT library
Define the pin number
Specify sensor type
Create DHT object

// Include the DHT library
#include <DHT.h>

// Define the pin connected to DATA
#define DHTPIN 2

// Define the sensor type
#define DHTTYPE DHT11

// Create DHT object
DHT dht(DHTPIN, DHTTYPE);

Setup and Loop

In setup(), we initialize serial communication and start the sensor.

In loop(), we read and display the sensor data.

Note: DHT11 has a 2-second sampling rate, so we add a delay between readings.

void setup() {
  // Initialize serial communication
  Serial.begin(9600);
  Serial.println("DHT11 Test!");
  
  // Start the sensor
  dht.begin();
}

void loop() {
  // Wait 2 seconds between readings
  delay(2000);
  
  // Read sensor data
  float humidity = dht.readHumidity();
  float temperature = dht.readTemperature();
  
  // Display the results
  Serial.print("Humidity: ");
  Serial.print(humidity);
  Serial.print(" %  Temperature: ");
  Serial.print(temperature);
  Serial.println(" °C");
}

Adding Error Handling

Sometimes sensors fail to read. It's good practice to check for errors using isnan() function.

Why add error checking?

Loose connections
Sensor malfunction
Timing issues

void loop() {
  delay(2000);
  
  float h = dht.readHumidity();
  float t = dht.readTemperature();
  
  // Check if readings failed
  if (isnan(h) || isnan(t)) {
    Serial.println("Failed to read from DHT sensor!");
    return;
  }
  
  // Display valid readings
  Serial.print("Humidity: ");
  Serial.print(h);
  Serial.print(" %  Temperature: ");
  Serial.print(t);
  Serial.println(" °C");
}

Testing Your Sensor

Upload and Test:

Upload the code to your Arduino
Open the Serial Monitor (Tools → Serial Monitor)
Set baud rate to 9600
You should see temperature and humidity readings every 2 seconds!

Common Issues:

"Failed to read": Check wiring, ensure sensor is powered
Strange values: Sensor might be damaged or wrong sensor type defined
No output: Check Serial Monitor baud rate matches code (9600)

Challenge: Try breathing on the sensor to see humidity increase!

Slides