RHT01 / DHT21 is another low-cost capacitive humidity sensor. It uses the same protocol as the RHT01/DHT11, which is the manufacturer’s own one-wire communication protocol. It is more accurate than the RHT01 with a slightly higher price.
The module is supported by LadyAda’s great DHT library. Choose the DHT21 option.
Power Supply: 3.3-5.5V DC
Output signal: digital signal via MaxDetect 1-wire bus
Sensing element:polymer humidity capacitor
Operating range: humidity 0-100%RH; temperature -40~80 Celsius
Accuracy: humidity +-3%RH (Max +-5%RH); temperature +-0.5 Celsius
Resolution: 0.1%RH; temperature 0.1 Celsius
Size: 1.05″ W x 2.30″ H x .55″ D
Lady Ada’s DHT library