Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!ll-xn!mit-eddie!apollo!nelson_p@apollo.uucp
From: nelson_p@apollo.uucp
Newsgroups: sci.electronics
Subject: electronic time capsule
Message-ID: <3a84f064.44e6@apollo.uucp>
Date: 26 Feb 88 19:15:00 GMT
Sender: user@apollo.uucp
Lines: 39
To: sci.electronics@news



 RE: My 'electronic time capsule'...

>If you put it under water, like I suggested, you will have an excellent
>time base available: the tides! These are fairly trivial to detect, and
>are predictable over many centuries!

 I am quite pleased with the creativity and originality shown by 
 some respondents to my question: 'How can I count off the time
 before my time capsule 'wakes up' a century or two down the
 road?'

 I'm not sure about tides.  First of all, there's the question
 of how to power it under water.  I had been planning to use 
 solar cells for a source of power; when the system finally
 wakes up it would transmit during the day.  
 
 Then there's the question of how to detect the tides.  Remember
 that systems involving moving parts would probably fail after
 a few decades in the best of conditions, and the ocean is NOT
 the best of conditions.  
  
 Which brings us to reliability.  Underwater it would be subject to
 barnicle growth and marine plants.  Ships sunk during WW II are
 totally encrusted now, a scant 45 years later.   And I don't 
 know what I would use for an antenna.
 
 
 Somebody else suggested tritium.  Watches used to be made with
 a substance which would light up in the presence of the alpha
 particles emitted by the tritium.  This bears some investigation:
 I will have to look up the half-life of tritium and also find out
 about the material used.  It would have to work over a century
 or more and not be subject to leakage or breakdown as a result
 of temperature cycling.  I mention the latter because I seem to
 recall that it was in a liquid medium.

 Good ideas though, keep 'em coming and thank you.

                                      --Peter Nelson