🚀 go-pugleaf

Can anyone out there help me with my search for something to use as an
electronic relative humidity sensor. So far my search has revealed the following
methods for building a sensor device for use in constructing an electronic
hygrometer I wish to interface to my PC:

1) I've been told of a synthetic rope-like material impregnated with graphite,
   powdered metal, and ionic salts for which the electrical resistance will
   change logarithmically with the relative humidity of the air around it.
   The engineer who informed me of this item works for a commercial
   meteorological instrumentation firm and cannot reveal the source of such
   material or the details of making it myself since his company 
   considers it a trade secret. The biggest advantage was that it doesn't
   require much in the way of temperature compensation and makes for an
   extremely accurate(less than .5% error), maintenance-free sensor.

2) An open, humidity-sensitive, thin-film-dielectric capacitor may be 
   constructed, but will require serious temperature change compensation and
   must be sealed inside some kind of housing that is almost airtight but would
   be porous enough to let the water molecules in the air through but keep
   keep out pollutants which could contaminate the delicate capacitor, like
   a porous ceramic case. This device could be used to control
   the frequency of an oscillator, whose output would be run through a
   frequency-to-voltage converter then through an A/D converter to give me
   the binary form I really need for my software to use. This sensor is 
   subject to false readings if the temperature compensation circiutry
   doesn't work perfectly. I don't think the accuracy is much better than 2%
   either plus there is a time lag for the water molecules in the air to
   penetrate the porous ceramic housing.

3) The ugliest way would be to employ a wet/dry pair of electronic thermometers
   and use software to calculate the relative humidity from the temperature
   difference. Yuck!!!! I really don't want to maintain a water supply and the
   necessary mechanical junk that would go along with this method.

Surely there must be some kind of easily obtainable or constructable relative
humidity sensor that can give an instantaneous, accurate (within 1%),
electronic signal output (I can convert from resistive, capacitive, or 
current generating) that would be inexpensive and maintenance-free.
If anyone out there knows of such a device, I would appreciate it very much.

Thanks, 
Neal Howard
email address => neal@cmptrc.lonestar.org 
or just post to sci.electronics, there may be others interested in this topic.
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