There have been packages build around a humidity sensor from Philips.
Maybe you can't get that introduction package anymore, but recently I've
seen that sensor still advertized. (Rather expensive. HFL40,- )
I have played with it in the past, but it really is terribly unsuitable.
It's a synthetic foil, metallized at both sides. Since the humidity makes the
thicknes of the foil vary, you have a capacitor of which the value will vary
with the humidity.
Problem is that you want to use it in the 80%-100% region. Once there will
come a moment that the local humidity exceeds 100% and liquid drops will
condensate on the foil (and the connection and/or the circuitry). You can
imagine that a correct working then is out of the question. This will remain
at least until all the problems have 'dried up'. Please tell me when that
ever will happen. Next, you'll have a problem with the long term stability.
Dirt on the foliage and erosion of the metallized surfaces.
If you really need to measure the humidity you would need a 'dew point
sensor system' which will be much too complicated.
I think the real option left is to use a good old hair hygrometer from wich
you derive electrical signals. For example, you could make the hand pass
optical sensors.
Regards, Wim.
----- wim@djo.wtm.tudelft.nl -----
(wim@morgana.nl)