DHT22 Sensor

The DHT22 est is a low-cost basic sensor for the humidity (%RH) and temperature. It use the capacitive effect for the humidity detection and a thermistor to measure the temperature.

This sensors output digital on an output pin on regular basis. No need for analog input a single digital input is needed. This sensor is easy to wire but required requires careful timing acquisition routine (it is a timing based protocol). The sensor use a one-wire proprietary protocol (it is not a 1Wire sensor), so you will need a seperate data pin for each DHT sensor connected to the microcontroler.

The sensor produce new data every 2 seconds, sensor readings can be up to 2 seconds old.

Using the sensor is simple: connect the first pin on left to 3V/5V, the second pin to microcontroler data input pin, the right pin must be connected to ground. A 4.7K - 10K pullup resistor must be connected between the data pin and VCC

Compared to the DHT11, this sensor is more precise, more accurate and works in a bigger range of temperature/humidity. It is also more expensive than DHT11.

Capacitive sensor means parts are exposed to the surrounding air, so the capacitive sensor will slowly degrade with the time. This cannot be avoided if we need to measure the humidity. Please note that 100% humidity also means liquid water which is never suited for electronic stuff (the sensor as the microcontroler).