A Guide for DHT22 Humidity and Temperature Sensor: DHT22 vs DHT11

The DHT22 is also known as AM2302 or RHT03, it includes a capacitive humidity sensor and a high precision temperature sensor. It uses dedicated digital module acquisition technology and temperature and humidity sensing technology to ensure high reliability and excellent long-term stability.

The DHT22 also has a capacitive sensing element and a high precision temperature measuring element connected to a high-performance 8-bit microcontroller. Thus, it has the advantages of excellent quality, ultra-fast response, strong anti-interference ability, and high-cost performance

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Waveshare DHT22 TEMPERATURE-HUMIDITY SENSOR technical specifications, attributes, parameters and parts with similar specifications to Waveshare DHT22 TEMPERATURE-HUMIDITY SENSOR.

• Ultra-small size

• Extremely low power consumption, and with a signal transmission distance of more than 20 meters thus it’s able to withstand the most demanding applications.

• The humidity sensor of 0 to 99.9 %RH with ±2% accuracy while the temperature sensor ranges from -40 to 80℃ with ±0.5℃ accuracy.

The DHT22 is a commonly used temperature and humidity sensor. The sensor comes with a dedicated NTC to measure temperature and an 8-bit microcontroller to output the values of temperature and humidity as serial data. The sensor is also factory calibrated and hence easy to interface with other microcontrollers.

The sensor can measure temperature from -40°C to 80°C and humidity from 0% to 100% with an accuracy of ±1°C and ±1%. So if you are looking to measure in this range then this sensor might be the right choice for you.

DHT22 sensor consists of two components for measuring; Humidity sensing component and the NTC temperature sensor (or a thermistor). There is an IC on the backside which makes the readings be able to read by the Raspberry pi.

While measuring the humidity, the humidity sensor comes into play. The humidity sensor consists of two electrodes with a moisture-holding substrate between them. So when the humidity changes, the conductivity of the substrate changes or you can say that the resistance between the electrodes changes. This change in resistance is then given to IC which makes it read by the Raspberry pi.

While measuring the temperature, the NTC temperature sensor or thermistor comes into play. The resistance of the thermistor changes with a change in the temperature. These are negative temperature coefficients (NTC) which means that their resistance decreases with the increase in temperature.

The DHT22 sensor is factory calibrated and outputs serial data and hence it is highly easy to set it up. The connection diagram for this sensor is shown below.

As you can see the data pin is connected to an I/O pin of the MCU and a 5K pull-up resistor is used. This data pin outputs the value of both temperature and humidity as serial data. If you are trying to interface DHT22 with Arduino Uno then there are ready-made libraries for it that will give you a quick start.

We have two versions of the DHTxx sensor series. They look a bit similar and have the same pinout, but have different characteristics. Here are the details:

The DHT22 is the more expensive version which obviously has better specifications. Its temperature measuring range is from -40°C to +125°C with +-0.5 degrees accuracy, while the DHT11 temperature range is from 0°C to 50°C with +-2 degrees accuracy. Also, the DHT22 sensor has better humidity measuring range, from 0 to 100% with 2-5% accuracy, while the DHT11 humidity range is from 20 to 80% with 5% accuracy. Or you can look at the chart below.

(1) Operating and storage conditions

 We don't recommend the applying RH -range beyond the range stated in this specification. The DHT22 sensor can recover after working in non-normal operating conditions to calibrated status but will accelerate sensors' aging.

(2) Attentions to chemical materials

 Vapor from chemical materials may interfere with DHT22's sensitive elements and debase DHT22's sensitivity.

(3) Disposal when (1) & (2) happens

 Step one: Keep the DHT22 sensor at a condition of Temperature 50~60Celsius, humidity <10%RH for 2 hours;

 Step two: After step one, keep the DHT22 sensor at a condition of Temperature 20~30Celsius, and humidity >70%RH for 5 hours.

(4) Attention to temperature's affection

 Relative humidity strongly depends on temperature. which is why we use temperature compensation technology to ensure accurate measurement of RH. But it's still much better to keep the sensor at the same temperature when sensing. DHT22 should be mounted at the place as far as possible from parts that may cause a change in temperature,

(5) Attentions to light

 Long time exposure to strong light and ultraviolet may debase DHT22's performance.

(6) Attentions to connection wires

 The connection wires' quality will affect communication quality and distance, high quality shielding-wire is recommended.

(7) Other attentions

 * Welding temperature should be below 260Celsius.

 * Avoid using the sensor under dew conditions.

 * Don't use this product in safety or emergency stop devices or any other occasion that failure of DHT22 may cause personal injury