On Mon, 12 Jan 2009 12:52:12 -0000, Steve Pardoe wrote:

Just as a matter of interest, can someone explain to me how these
humidity sensors work?

Googling about they appear to be capacitive, the capacitance of the device
varies with humidty in a known manner. Build an oscilator with the humidty
sensitive device in the control loop and the frequency of the oscilator
will vary in relation to the humidty. Then simply measure the frequency of
your oscilator to get the humidty reading.

http://www.directindustry.com/prod/e...ensor-for-mass
-applications-smd-component-13965-44881.html

http://www.rapidonline.com/Electroni...idity-Sensors/
Humidity-sensor/80511/kw/61-0984

http://www.rapidonline.com/Electroni...idity-Sensors/
Humidity-sensor/30168/kw/61-0960

--
Cheers
Dave.