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PICList Thread
'[pic]:Too hot to wake up'
2000\08\01@183609 by jamesnewton

face picon face
-----Original Message-----
From: Alice Campbell []
Sent: Tuesday, August 01, 2000 15:32
Subject: [pic]:Too hot to wake up
Importance: Low

James, could you forward this for me? i still cant get to the
list myself.  grumble grumble.

Esteemed Piclist:

Once i discovered that the ADC in my datalogger wouldnt run
at 33 kHz, i replaced the watch crystal with a 4 MHz crystal.
There are two caps, 47 pF.  The dataloggers live outside,and
sleep 7 minutes to one hour.  Its pretty hot out, about 100
deg or more in the daytime.  I have a temperature
compensation routine to correct the sleep time for
temperature, that isn't the problem.  While the circuits run
pretty well under about 80 deg, once they get hot, they only
sluggishly wake up, one hardly wakes up at all.  I tried a
.1uF cap across the pic's power pin to ground, to boost it a
little, helped a little but not fixed.  I changed the caps to
33 pf but thats worse.  The capacitance of my finger will
generally wake up the more sluggish unit, but i really cant
stand around all day slapping the thing to make it run.  Im
starting to reach for the big rubber mallet, does anyone have
any suggestions?


-- hint: To leave the PICList>

2000\08\02@171321 by Barry Gershenfeld

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The "PIC Mid-Range Family" document actually has quite a bit to say about
oscillators.  The most revealing thing I found was this:

  The main difference between the LP, XT, and HS modes is the gain
  of the internal inverter of the oscillator circuit which allows
  the different frequency ranges.

Meaning, that it isn't "illegal" to try a higher gain mode.  It does
use more power, though.  They list the gains like this:

HS High Gain
XT Medium Gain
LP Low Gain

RC - don't use; it's a different configuration inside.

Also, "noise is good" -- it helps the oscillator start!  (Bypassing
works against you, here).


At 03:33 PM 8/1/00 -0700, you wrote:
>{Original Message removed}

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