DHT11: Temperature and Humidity Sensor Explained

The DHT11 is a low-cost digital temperature and humidity sensor that is widely used in weather monitoring, home automation, and IoT applications. It provides real-time temperature and humidity readings using a simple one-wire communication protocol, making it easy to interface with microcontrollers like Arduino, ESP32, Raspberry Pi, and STM32.

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🔹 1. What is the DHT11?

• DHT11 is a digital temperature and humidity sensor with a built-in capacitive humidity sensing element and a thermistor for measuring temperature.
• Uses a single digital data pin for communication, making it easy to integrate into microcontroller-based projects.
• Operating voltage: 3.3V – 5V, making it compatible with Arduino, ESP32, and Raspberry Pi.

📌 Key Features:

• Temperature Range: 0°C to 50°C (±2°C accuracy). More about Accuracy->
• Humidity Range: 20% to 90% RH (±5% accuracy). More about Accuracy->
• Supply Voltage: 3.3V – 5V.
• Sampling Rate: 1 reading per second (1Hz).
• Communication Protocol: Single-wire digital signal.
• Low power consumption.

📌 Common Applications:

• Weather monitoring stations.
• Home automation and smart homes.
• Greenhouse and indoor climate monitoring.
• IoT-based environmental monitoring.
• Industrial humidity control systems.

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🔹 2. DHT11 Pinout & Functions

The DHT11 sensor comes in two forms:

1. Standalone DHT11 sensor (4 pins)
2. DHT11 module (3 pins with built-in pull-up resistor).

Pin No.	Name	Function
1	VCC	Power Supply (3.3V – 5V)
2	Data (OUT)	Digital Data Output (One-wire communication)
3	NC (Not Connected)	Unused (leave unconnected)
4	GND	Ground (0V)

📌 Note:

• If using a standalone DHT11, connect a 4.7kΩ – 10kΩ pull-up resistor between the Data pin and VCC.
• DHT11 modules already include a pull-up resistor, so no additional resistor is needed.

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🔹 3. Wiring the DHT11 with an Arduino

🛠 Required Components

• 1x Arduino (Uno, Nano, Mega, ESP32, etc.)
• 1x DHT11 Sensor
• 1x 10kΩ Resistor (if using the 4-pin version)
• Jumper Wires

🛠 Wiring:

DHT11 Pin	Arduino Pin
VCC (Pin 1)	5V (or 3.3V for ESP32/Raspberry Pi)
Data (Pin 2)	Digital Pin (e.g., D2 on Arduino)
GND (Pin 4)	GND

📌 For standalone DHT11: Connect a 10kΩ pull-up resistor between Data and VCC.

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🔹 4. Arduino Code to Read DHT11 Sensor

We use the DHT library to easily communicate with the sensor.

🛠 Install the DHT Library

1. Open Arduino IDE.
2. Go to Sketch → Include Library → Manage Libraries.
3. Search for “DHT sensor library by Adafruit” and install it.

✅ Arduino Code for DHT11

#include <DHT.h>

#define DHTPIN 2        // DHT11 connected to digital pin 2
#define DHTTYPE DHT11   // Define sensor type

DHT dht(DHTPIN, DHTTYPE);

void setup() {
    Serial.begin(9600);
    dht.begin();
}

void loop() {
    float temperature = dht.readTemperature();  // Read temperature (Celsius)
    float humidity = dht.readHumidity();       // Read humidity

    if (isnan(temperature) || isnan(humidity)) {
        Serial.println("Failed to read from DHT11 sensor!");
        return;
    }

    Serial.print("Temperature: ");
    Serial.print(temperature);
    Serial.println(" °C");

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

    delay(2000);  // Wait 2 seconds before next reading
}

📌 How it works:

• The dht.readTemperature() function reads the temperature in Celsius.
• The dht.readHumidity() function reads the humidity percentage.
• If the sensor fails to respond, it prints an error message.
• Data is updated every 2 seconds (recommended by the DHT11 specs).

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🔹 5. DHT11 vs DHT22: Which One to Use?

The DHT22 (AM2302) is a more accurate and wider-range version of the DHT11.

Feature	DHT11	DHT22 (AM2302)
Temperature Range	0 to 50°C	-40 to 80°C
Temperature Accuracy	±2°C	±0.5°C
Humidity Range	20% to 90% RH	0% to 100% RH
Humidity Accuracy	±5% RH	±2% RH
Sampling Rate	1 Hz (1s)	0.5 Hz (2s)
Cost	Cheaper (~$2-3)	More Expensive (~$5-7)

📌 Verdict:

• Use DHT11 for simple low-cost projects where ±2°C accuracy is acceptable.
• Use DHT22 if you need better accuracy and wider temperature range.

🌡️ DHT11 vs. DHT22: Detailed Comparison

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🔹 6. Common Issues & Fixes

❌ Sensor not responding? ✅ Check wiring, pull-up resistor, and power supply.

❌ Incorrect temperature/humidity readings? ✅ Allow the sensor to stabilize for a few seconds after startup.

❌ Slow updates? ✅ DHT11 updates every 1 second. Use a faster sensor (DHT22 or AM2302) if needed.

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🎯 Conclusion

• DHT11 is a simple, low-cost digital sensor for temperature and humidity.
• Easy to connect with only 1 data pin.
• Best for beginner projects, home automation, and IoT applications.
• For better accuracy, use DHT22 instead.