The DHT22 is a digital sensor so it sends 1’s and 0’s, but it is very important to know how it sends the digital data. Note that while transmitting bytes, the sensor sends the most significant bit first. The sensor then sends 40 bits (5 bytes) of data continuously in the data line. Once detecting the response signal from the sensor, the MCU should be ready to receive data from the sensor. Remember that the MCU pin must be configured to input after finishing the “Start“ signal. Next, the sensor responds to the MCU “Start“ signal by pulling the line low for 80 us followed by a logic high signal that also lasts for 80 us.
The MCU first pulls the data line low for at least 18 ms and then pulls it high for next 20-40 us before it releases it. The MCU pin must be configured as output for this purpose. The MCU initiates data transmission by issuing a “Start” signal. The following timing diagrams describe the data transfer protocol between a MCU and the DHT22 sensor. The protocol must be implemented in the firmware of the MCU with precise timing required by the sensor. It has got its own proprietary 1-wire protocol, and therefore, the communication between the sensor and a microcontroller is not possible through a direct interface with any of its peripherals. The sensor provides fully calibrated digital outputs for the two measurements. It can measure temperature from -40-80 ☌ with an accuracy of ☐.5☌ and relative humidity ranging from 0-100% with an accuracy of ☒%. The DHT22(AM2302, RHT03) sensor comes in a single row 4-pin package and operates from 3.3 to 5.5V power supply.
About DHT22 (AM2302, RHT03) relative humidity and temperature sensor:
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