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From: row0@ns1.cc.lehigh.edu (RICHARD O. WHITE)
Newsgroups: sci.electronics
Subject: Re: Help with ultra-long timing
Message-ID: <1993Apr6.171129.108273@ns1.cc.lehigh.edu>
Date: 6 Apr 93 17:11:29 GMT
Organization: Lehigh University
Lines: 49


In article <1993Apr5.083324.48826@kuhub.cc.ukans.edu>, wellison@kuhub.cc.ukans.e
du writes:
>I have a project that was drooped in my lap that is somewhat a pain to design.
>What I am looking for is a stable ultra-long solid state timer. What they want
>to do is to place this thing on the Antartic ice shelf and measure the amount
>of snow fall over a period of six weeks. Every two weeks, they want to trip a
>selonoid to discharge different colored pellets by gas pressure out across the
>snow. Then by digging down into the snow, the snow fall amount can be measured
>as they come to the different color pellets.
>
>The problem is trying to build a timer that would stand the cold (-40 degrees)
>and a power source that wouldn't drain. I have looked at the XR-2204 timers and
>the standard NE556 dual timers, but thier temp specs won't go that low. Also,
>two weeks equates to 1,209,600 seconds per firing, which means one big timing
>cap ! I have found 2.2 farad (yes, Farad !) caps that have a working voltage of
>5 volts and are small in size. But again, the time of discharge at -40 or lower
>degrees isn't linear. I was thinking of using several timers chained together
>to fire the selonid at the end of the timing period, but that blasted cold and
>the drain on a battery over six weeks is the pain. One possibility would be to
>use solar panels, but this is during the six month twilight. Anyone have any
>good ideas ?
>
>Thanks in advance...
>
>-=-= Wes =-=-
>
just a suggestion:
take a motorola mc14536B set it up to give you a pulse once every sec or ten
secs with either a RC or xtal clock input. then feed to a MC14521B as clock
input and decode output for 1,209,600 sec output ,might have to add a few 'and'
gates or decoder chips to get output and reset pulse back to the'521 to restart
cycle... Trigger a oneshot from the decoded riseing edge ;the one shot then
goes to a mosfet to drive the mechanism to fire the pellet launcher..
these ckts require uAmps of current,between 5 - 15 volts, so a 12 volt
gel cell of a few Amphours would last the six weeks.
Then take the ckt board & battery wrap in 3" or 4" of foam or build a box
of out of the stuff...with plywood or metal exterior...
build a small heater out of 10-50 Watt resistors in series to keep the battery
and ckts warm.
2nd thought use 2 batteries one for heater one for timer and pellet trigger.

Insolate-insolate.......even though the chips state that the - AL
rated devices are good to -55 C.. The batteries have a considerable reduction
in capacity...oh make sure the area inside has minium air leakage..

hope this helps
RW     ( is this to long winded for the net??)(be gentle)...
-- 
