Read temperature and humidity with the DHT11

The DHT11 measures both temperature and humidity and sends the result over a single data wire. It's the heart of weather stations, greenhouse monitors and smart thermostats.

What you'll learn

• How to install a library with the Library Manager
• How to read a digital sensor
• How to handle a failed reading

What you need

• ESP32-DevKitC V4 board and USB cable
• DHT11 temperature and humidity module (KY-015)
• Breadboard
• 3 jumper wires

Step 1: Install the library

Open Tools → Manage Libraries, search for DHT sensor library and install the one by Adafruit. When asked, also install its dependency, Adafruit Unified Sensor.

Step 2: Wiring

The module has three pins. Check the labels printed on your module: usually S (signal), the middle pin (power) and - (ground).

Step 3: The sketch

#include <DHT.h>

const int DHT_PIN = 27;
DHT dht(DHT_PIN, DHT11);

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

void loop() {
  delay(2000); // the DHT11 needs about 2 seconds between readings

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

  if (isnan(humidity) || isnan(temperature)) {
    Serial.println("Couldn't read the sensor, check the wiring");
    return;
  }

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

How it works

The library asks the sensor for a reading, and the sensor answers with a short burst of pulses on the data wire. If something goes wrong, the library returns NaN ("not a number"), which the sketch checks with isnan(). The DHT11 is accurate to about ±2 °C and ±5 % humidity, which is fine for a room monitor.

Try this next

• Breathe gently on the sensor and watch the humidity rise.
• Add the LED from lesson 1 and switch it on when the temperature goes above 26 °C.

Troubleshooting

• "Couldn't read the sensor": check that S is on GPIO 27 and the power pins aren't swapped.
• Compile error about DHT.h: the library isn't installed. Repeat step 1.