AVR-Chat

hi everybody:
does anybody have information about humidity sensors with 2 pin ?
I just know that they act as a capacitor ,but I don't know how I 
should measure it ,and how I should do that with avr .
whould you mind sharing your experience about that with me ?
If you send me any useful information about measuring & calibrating 
these sensors and build a hygrometer ,I'll be very 

thankful.
Aila Hasanalizadeh