DHT11 temperature — Arduino code

What you need

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

Wiring

Test code virtually first. For real hardware, ask a trusted adult, unplug power before changing wires, and check the labels or datasheet for your exact part.

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

The code

#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
}

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.

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