Humidity and Temperature sensors
This page covers the low cost DHT temperature & humidity sensors . These sensors are very basic and slow, but are great for hobbyists who want to do some basic data logging.
The DHT sensors are made of two parts, a capacitive humidity sensor and a thermistor. There is also a very basic chip inside that does some analog to digital conversion and spits out a digital signal with the temperature and humidity. The digital signal is fairly easy to read using any microcontroller.