DHT11 temperature — Arduino code

The DHT11 measures temperature and humidity together and reports both over a single data wire. It needs the DHT sensor library, which you install once from the Arduino IDE.

What you need

• Arduino Uno
• 1 × DHT11 module
• 3 jumper wires
• DHT sensor library (Adafruit)

Wiring

1VCC or + to 5 V
2GND or − to GND
3DATA or S to digital pin 2
4In the IDE: Tools → Manage Libraries → search "DHT sensor library" → Install.

The code

dht11-temperature.ino

#include <DHT.h>

#define DHTPIN 2
#define DHTTYPE DHT11

DHT dht(DHTPIN, DHTTYPE);

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

void loop() {
  float temperature = dht.readTemperature();  // °C
  float humidity = dht.readHumidity();        // %

  if (isnan(temperature) || isnan(humidity)) {
    Serial.println("Sensor not responding");
  } else {
    Serial.print(temperature);
    Serial.print(" C  ");
    Serial.print(humidity);
    Serial.println(" %");
  }

  delay(2000);  // DHT11 needs 2 seconds between reads
}

Try it in the simulator

Line by line

DHT dht(DHTPIN, DHTTYPE);: Sets up the sensor object for a DHT11 on pin 2.
dht.begin();: Starts talking to the sensor once, in setup().
dht.readTemperature();: Returns degrees Celsius. Pass true for Fahrenheit.
isnan(temperature): Catches failed reads so a loose wire does not print nonsense.
delay(2000);: The DHT11 can only be read about once every two seconds.

When it does not work

It prints nan or "Sensor not responding": Usually the data pin is on the wrong socket or the delay is too short. Check the wire and keep delay(2000).
How accurate is a DHT11?: About ±2 °C and ±5 % humidity. For sharper readings use a DHT22, which uses the same code with DHTTYPE DHT22.

Want the theory behind it?

Read the lesson

What you need

Wiring

The code

Line by line

When it does not work

More code examples