How to Use DHT22: Examples, Pinouts, and Specs

The DHT22 is a reliable sensor for measuring temperature and humidity. This sensor is suitable for a wide range of applications due to its ability to provide long-term stability and relatively high measurement accuracy. Common applications include HVAC systems, weather stations, home environment monitoring, and IoT projects.

• Temperature Range: -40 to 80°C
• Humidity Range: 0 to 100% RH
• Voltage: 3.3 to 6V DC
• Current: 2.5mA max during conversion (while requesting data)
• Accuracy: ±0.5°C (temperature), ±2-5% RH (humidity)
• Resolution: 0.1°C (temperature), 0.1% RH (humidity)
• Sampling Rate: ≤ 0.5 Hz (once every 2 seconds)
• Output: Digital signal via a single data pin

1. Connect the VDD pin to a 3.3V or 5V power supply.
2. Connect the DATA pin to a digital I/O pin on a microcontroller.
3. Connect a pull-up resistor (typically 10kΩ) between the DATA pin and VDD.
4. Connect the GND pin to the ground of the power supply.

• Ensure that the power supply is stable and within the specified voltage range.
• Avoid placing the sensor in direct sunlight or near heat sources to prevent inaccurate readings.
• Use a pull-up resistor on the DATA pin to ensure reliable data transmission.
• Allow the sensor to acclimatize to the environment for accurate readings.

#include "DHT.h"

#define DHTPIN 2     // Digital pin connected to the DHT sensor
#define DHTTYPE DHT22   // DHT 22 (AM2302)

DHT dht(DHTPIN, DHTTYPE);

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

void loop() {
  // Wait a few seconds between measurements.
  delay(2000);

  // Reading temperature or humidity takes about 250 milliseconds!
  float humidity = dht.readHumidity();
  // Read temperature as Celsius (the default)
  float temperature = dht.readTemperature();

  // Check if any reads failed and exit early (to try again).
  if (isnan(humidity) || isnan(temperature)) {
    Serial.println("Failed to read from DHT sensor!");
    return;
  }

  // Compute heat index in Celsius (isFahrenheit = false)
  float heatIndex = dht.computeHeatIndex(temperature, humidity, false);

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

Note: This code requires the DHT sensor library, which can be installed via the Arduino Library Manager.

• Inaccurate Readings: Ensure the sensor is not exposed to direct sunlight or heat sources. Allow it to acclimatize to the environment.
• No Data: Check the wiring, especially the pull-up resistor on the DATA pin. Ensure the power supply is within the specified range.
• Erratic Readings: Ensure there are no sources of electromagnetic interference near the sensor. Use shielded cables if necessary.

Q: Can I use the DHT22 sensor outdoors? A: Yes, but it should be protected from direct sunlight, rain, and condensation.

Q: How long should I wait between readings? A: The DHT22 has a sampling rate of up to once every 2 seconds. It is recommended to wait at least this long to avoid self-heating and to ensure accurate measurements.

Q: What should I do if the sensor is not responding? A: Check the power supply, wiring, and pull-up resistor. If the issue persists, replace the sensor as it may be defective.

For further assistance, consult the manufacturer's datasheet and technical support resources.