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From: bew4568@summa.tamu.edu (WILSON, BRUCE ERIC)
Newsgroups: sci.electronics
Subject: Re: Humidity Sensors in Clothes Dryers
Summary: Humidity Sensors
Keywords: Sensors
Message-ID: <14605@helios.TAMU.EDU>
Date: 12 Apr 91 20:18:59 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
> 
> 
> Any suggestions/reply would benefit 17 frustrated Eng Students
> (and probably give 'em a better mark too!!!!!!!)
> 
> Thanks
> 
> Scott Reynolds 
> 4th Year Electronic Eng/Computer Sci. Student RMIT Aust.

Well, a dryer that mon and dad had 10 years ago had 2 contacts on the back 
wall of the tumbler.  I suppose the contacts were sufficiently conductive with 
wet clothing, and the timer (mechanical) was prevented from advancing.  When 
the clothes were dry to some extent the timer continued for a fixed period, to 
make sure everything got dry.  The sensors were rather elongated, and sloped 
away from the rear wall (in the direction of rotation, that is) to keep a good 
contact with the cloths.


               |
               |______
               |      //
               |     //
 Back wall---->|    //<--- Sensor strips (2, one above the other)
               |   //
               |  //
 Rotation      | //
  Direction |  |//
            |  |/
           \/

Bruce