-> i can't tie a cheap hygrometer using a hair to a computer ;) 
  
Why not? Just buy one of those cheap hygrometers (which usually use a 
kind of strip with paper glued to metal), and hook a small 
potentiometer to it, so the resistance will change with the humidity. 
Then digitize the signal and feed it into your computer. 
  
There are other possibilities, too, such as using a solution of a 
deliquescent salt as your sensor. The electrical conductance will vary 
with the humidity. 
  
                            dow 
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