DHT22 – Pin Diagram, Circuit and Its Applications

With the growth in digital technology, today many devices are easily available as  Integrated chips. These chips are small in size but have higher performance compared to there earlier versions. As more number of devices are integrated on the single-chip the heat dissipated by them became a cause of concern. If the heat is more than recommended values the minute connections between components get damaged which leads to damage of the whole chip. In such scenarios, it becomes crucial to monitor the temperature and humidity values of the devices. For this,  temperature and humidity sensors are used. One of such sensor that is highly preferred for such task is DHT22 sensor.

What is DHT22?

DHT22 is a highly accurate humidity and temperature sensor. This sensor measures relative humidity values. It uses the capacitive sensor element to measure Humidity. For measuring temperature it uses NTC thermistor. This sensor can be used in harsh conditions also. It is available as a sensor as well as Module.

Block Diagram

The DHT22 sensor is the successor of the DHT11 sensor. DHT22 is available as a sensor as well as a module. The functioning of both sensor and module of DHT22 are similar. The difference lies in the internal circuitry. The module contains an in-built filtering capacitor and pull-up resistors. Whereas in sensor these have to be connected externally. DHT22 sensor and module both have 8-bit microcontroller connected to it to do the calculations. DHT22 module comes as 3-pin package whereas sensor comes as 4-pin package. The module has a high measuring range, better accuracy and a little bit costlier than the sensor.

This sensor’s performance can get degraded when it is exposed to UV and strong light for a long time. For error-free and disturbance-free communication, it is recommended to use high-quality shielding wire for connections.

Circuit Diagram

DHT22 uses a single wire serial interface to transfer data to the microprocessor unit. The DATA pin available on the sensor is used to transfer the data and is connected to the microprocessor.

When power is applied the sensor initially stays in the unstable status for one second, during this time no instructions should be sent to the sensor. For single time communication between MCU and sensor, it takes 5msec. The starts sending data only after receiving the start signal from MCU.

When this sensor is used for RH range higher than the recommended it can increase the aging of the device. DHT22 sensors sensitivity can change when it is exposed to chemical vapor.

Pin Diagram

DHT22 is available as a 4-pin single rowed package. This sensor module calculates temperature values in Celsius. These values are then converted into Fahrenheit and kelvin using conversion formulas. The pin configuration of this sensor is given below

• Pin-1- VDD- is the power supply pin. DC voltage is applied to his pin.
• Pin-2- DATA/SDA- is the serial data pin. This pin is connected to the microcontroller to transfer data from the sensor to the controller.
• Pin-3- NC- is also known as the no connection pin which is left unconnected.
• Pin-4-GND-is the ground pin. This pin is connected to the ground.

Specifications of DHT22

DHT22 is also known as AM2302. Specifications of this sensor are given below-

• It works with a DC supply voltage of 3.3V to 5.5V.
• DHT22 requires a 1.5mA of current for working.
• When in standby mode this sensor consumes 0.02mA of current.
• This sensor gives digital output values.
• Operating temperature range of this sensor is from -40°C to 80°C.
• It can detect humidity from 0-100%RH.
• This sensor can measure humidity with accuracy up to +-2% RH.
• Temperature accuracy up to <+-0.5 celsius can be measured with DHT22.
• This sensor measure humidity with a resolution of 0.1%RH and temperature with 0.1-celsius resolution.
• DHT22 has a humidity hysteresis of +-0.3%RH
• This sensor has an average sensing period of 2sec.
• This sensor is available in two sizes- small size of 14*18*5.5 mm and large size of 22*28*5 mm.
• The capacitive sensor element is used as the sensing element in DHT22.
• Wet NTC temperature measurement device is used in DHT22 for temperature calculation.
• This sensor can transmit the signal up to 2 meters.
• DHT22 has a single – wire serial interface, which makes it integration with microprocessors and microcontrollers east, simple and fast.
• This sensor also has the anti-interference ability.
• As relative humidity depends on the temperature, this sensor is temperature compensated and calibrated in accurate calibration chambers to get accurate humidity measurements.
• This calibration coefficient is saved in the form of program OTP memory. Internal sensor detection signals can call this calibration coefficient.
• DHT22 is highly accurate with excellent quality and fast response.
• DHT22 has outstanding long-term stability.
• DHT22 gives a digital output which is highly calibrated.
• This sensor is available as a 4-pin package which is fully interchangeable.

Applications of DHT22

For its reliability and stability, DHT22 utilizes the digital signal collecting technique and Humidity sensing technology. Its small size and low energy consumption make it suitable for harsh applications. Some of the applications of this sensor are listed below-

• DHT22 is applied in HVAC.
• Testing and Inspection equipment use DHT22 for measuring temperature and humidity values.
• This sensor is used in home appliances and consumer products for measuring temperature and humidity values.
• In medical units to detect the humidity values in isolation units of patients, DHT22 is used.
• For medical devices used by patients who are sensitive to high temperatures and suffering from certain lung diseases, DHT22 is used to check the air humidity levels.
• This senor is used in weather stations, refrigerators, Fax machines, food processing units, etc…
• In pharmaceutical units to maintain the temperature and humidity values in the required range this sensor is used.

Alternative IC

Some of the IC available in the market that can be used as an alternative to this sensor are SHTW2, SHT3X, SHT85.

When used with Arduino the DATA pin of this sensor is connected to the digital IO pin of the MCU. Along with this, DHT libraries are present which are used for communication between MCU and the sensor. Further details on the electrical characteristics of this sensor can be found in its datasheet. What is an NTC thermistor?