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From: afpauls@lims01.lerc.nasa.gov (PAUL SCHWARTZ)
Newsgroups: sci.electronics
Subject: Re: Humidity Sensors in Clothes Dryers
Summary: Humidity Sensors
Keywords: Sensors
Message-ID: <1991Apr17.161514.756@eagle.lerc.nasa.gov>
Date: 17 Apr 91 19:04:14 GMT
References: <1991Apr12.113251.16467@minyos.xx.rmit.oz.au>
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In article <1991Apr12.113251.16467@minyos.xx.rmit.oz.au>, s882823@minyos.xx.rmit.oz.au (Scott Reynolds [.../* sbr */...]) writes...
>I have a question hopefully someone out there in net-land can answer?
> 
>We (a group of 17 Electronic Eng 3rd Year Students) have a 12 week
>design project for designing a Micro Controller for a domestic
>clothes dryer. After extensive market research (looking in the
>local dept. store) found that humidity controlled dryers were
>rare - hence our desire to use the exhaust air humidity as a indication
>of the dryness.
> The problem arises as to selecting an appropriate sensor, considering
> the nasty environ.
> Does anyone know of sensors used in commerically availiable products
> 
> 
The dryer which I own will automatically stop when the clothes are dry but 
it doesn't use a humidity sensor, it uses a temperature sensor.  

The dryer has a mechanical timer. When the exhaust reaches a certain 
temperature the heating element turns off and the timer advances.  
When the temperature get below a certain level the heating element will
turn back on and the timer will stop advancing.  This process will 
continue until the timer turns everything off.  

I can say from using the dryer the system work very well

Paul Schwartz