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From: johnh@macadam.mpce.mq.edu.au (John Haddy)
Newsgroups: sci.electronics
Subject: Re: Help with ultra-long timing
Date: 6 Apr 1993 03:39:14 GMT
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References: <1993Apr5.083324.48826@kuhub.cc.ukans.edu> <C513wI.G5A@athena.cs.uga.edu>
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In article <C513wI.G5A@athena.cs.uga.edu>, mcovingt@aisun3.ai.uga.edu (Michael Covington) writes:
|> (1) Don't use big capacitors.  They are unreliable for timing due to
|> leakage. 
|> 
|> Instead, use a quartz crystal and divide its frequency by 2 40 times
|> or something like that.
|> 
|> 1 MHz divided by 2^40 = 1 cycle per 2 weeks, approximately.
|> 
|> (2) I wouldn't expect any components (other than batteries or electrolytic
|> capacitors) to fail at -40 C (or -40 F for that matter either :) ).
|> The battery is going to be your big problem.  Also, of course, your
|> circuit shouldn't depend on exact values of resistors (which a crystal-
|> controlled timer won't).
|> 

... Wouldn't a crystal be affected by cold? My gut feeling is that, as a
mechanically resonating device, extreme cold is likely to affect the
compliance (?terminology?) of the quartz, and hence its resonant frequency.

|> -- 
|> :-  Michael A. Covington         internet mcovingt@ai.uga.edu :    *****
|> :-  Artificial Intelligence Programs       phone 706 542-0358 :  *********
|> :-  The University of Georgia                fax 706 542-0349 :   *  *  *
|> :-  Athens, Georgia 30602-7415 U.S.A.     amateur radio N4TMI :  ** *** **


JohnH

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