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'[PIC]: Too hot to wake up'
2000\08\02@155208 by Dan Michaels

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Alice Campbell wrote:
{Quote hidden}

Hello Alice,

I have never tried sleep mode with a PIC, myself, nor tried
operating a PIC at 100 degF [although all I would have to do is
open the outside door around here right now], but the first thing
that occurred to me was

- Do the loggers start up reliably from a "hard" reset at these
 temperatures? You may be looking at the wrong problem.

- Also, you might want to look at using an industrial temp range
 PIC - it may be way over 100 degF inside the box, esp in the sun.
 [might set up one of your channels to measure internal box temp].

- Also, maybe you battery is pooping out at those temps.

- Also, you might check the datasheets re operating temperatures
 for the crystals you are using, and possibly try other xtals.
 Someone else may know if resonators work better at hi temps.
 Might also check

 http://www.murata.co.jp

- Also, when you went from 32 Khz, you did change over from the LP
 to the XT oscillator, didn't you? If all else fails, you might
 even try the HS oscillator - [really make the xtal's day].

- Also, interestingly, the PIC datasheet says using lower value caps
 should "decrease" the startup time - but yours appears to work the
 other way. Hmmmm????? Still, you might try the low end value shown
 in the datasheet, 15 pF.

- [the key to fixing this sort of thing is to just keep asking
 questions, and testing things - and keep your sun hat on].

Maybe someone else has had hi-temperature experience with PICs ????????

best regards,
- Dan Michaels
Oricom Technologies
===================

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2000\08\02@180034 by Matt Bonner

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Dan Michaels wrote:

> Maybe someone else has had hi-temperature experience with PICs ????????

We've successfully long-term tested 16C74s at 150 degC and
16F877s at 175 degC (hi temp versions), and have had no
start-up problems either from a cold start or from sleep
mode.  Both designs used standard crystal configurations:
3.6864MHz (XT) for the '74 and 11.0592MHz (HS) for the
'877.  As Dan said - check that oscillator fuse.

A commercial temperature rated PIC should operate much
higher than 100 deg F.  If the problem is temperature
related, the battery and/or the crystal would be likely
suspects (again, as Dan suggested).  How much start-up
current does the logger require?

Or, are you talking about the crystal on an external ADC?
If you are, I've seen start-up problems with Analog Device's
7713 ADC, both from sleep and power-up.

--Matt

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2000\08\02@201736 by Dan Michaels

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Following forwarded to piclist, as proxy for Alice:
==================================================


> I have never tried sleep mode with a PIC, myself, nor tried
> operating a PIC at 100 degF [although all I would have to do is
> open the outside door around here right now], but the first thing
> that occurred to me was
>
> - Do the loggers start up reliably from a "hard" reset at these
>   temperatures? You may be looking at the wrong problem.

Yes.  for reasons lost in time, the mclr button is used as an
interrupt for this circuit, and triggers a dump to the rs232
line.  it incidentally will fix any error conditions and
leave the machine in a known, initialized state, but NOT
change the main count. see, the calibration of the sleep
timer relies on generating a wdt timeout, and parsing out the
wdt timeout was enough of a nuisance that it was easy to
parse out the mclr reset and use it instead of an interrupt.
as long as all the subroutines have flags, i can find where
it left off, which is inevitably in the sleep routine.

>
> - Also, you might want to look at using an industrial temp range
>   PIC - it may be way over 100 degF inside the box, esp in the sun.
>   [might set up one of your channels to measure internal box temp].
>
yes, i am considering this--actually, all i have to do is
save the sleep timer calibration variable.  But i am annoyed
that the same pic + board worked fine with the 33kHz crystal
and 47 uf caps.  the change to the circuit is just the
crystal and caps, nothing else. i promise, i was there
soldering.


> - Also, maybe you battery is pooping out at those temps.
>
battery voltage is great.  the stupid thing just sleeps all
the time.  I can tell from the battery voltage, which is
maybe 8.7 volts and 3 weeks doesnt even dent it.  i think i
licked the earlier power leak from not trissing all the pins
and setting them low.

> - Also, you might check the datasheets re operating temperatures
>   for the crystals you are using, and possibly try other xtals.
>   Someone else may know if resonators work better at hi temps.
>   Might also check

hmm, have some 4.1 colorburst crystals in bottom of bin,...
<mumbles about all those timing loops for 2400 baud>

>   http://www.murata.co.jp
>
> - Also, when you went from 32 Khz, you did change over from the LP
>   to the XT oscillator, didn't you? If all else fails, you might
>   even try the HS oscillator - [really make the xtal's day].
>
xt is enabled.  i was about to try HS next, but it seemed a
little paltry.  Another thing i am thinking about is locating
and trying 100khz crystals, i dont need speed, i need
reliability.  Junk box just doesnt have any 100kHzs.

> - Also, interestingly, the PIC datasheet says using lower value caps
>   should "decrease" the startup time - but yours appears to work the
>   other way. Hmmmm????? Still, you might try the low end value shown
>   in the datasheet, 15 pF.

This i will try.  maybe i just didnt push it far enough, or
there is a peak and im not across it yet.  Another thing i
will try is unbalanced caps, say a 15 pf and a 20 pf, to rock
the boat.  also a cheezy carbon resistor on the inner pin, to
generate some noise.

>
> - [the key to fixing this sort of thing is to just keep asking
>   questions, and testing things - and keep your sun hat on].
>
i was afraid of that.

thanks, i will keep slogging and report progress.

alice

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2000\08\03@025928 by Tsvetan Usunov

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> We've successfully long-term tested 16C74s at 150 degC and
> 16F877s at 175 degC (hi temp versions), and have had no
> start-up problems either from a cold start or from sleep
> mode.  Both designs used standard crystal configurations:
> 3.6864MHz (XT) for the '74 and 11.0592MHz (HS) for the
> '877.  As Dan said - check that oscillator fuse.

Are you sure 150 C ???
We have performed several projects run up to 125C but SUCCESSFULLY
LONG-TERM TEST on 150 C sounds like real magic.
I'm interested what PCB laminate you have used for your PCB as FR-4 would
melt and deformate at temperatures over 130C.
What type of capacitors (especially electrolyte caps) you have been used?
All quartz crystal specs shows up to 70C operation. What happend with them
at 150C after 1 week operation?
Even don't dare to ask for the connectors, switches and etc. plastics as
for high temperature the recommended parameters derate down to 10% of the
normal (for instance the carrying current).

Tsvetan
---
PCB prototype for $26 at http://run.to/pcb

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2000\08\03@075906 by Simon Nield

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Apologies if someone has suggested this already, i only get time to skim read most of the posts.

If you are currently using a crystal and you suspect that it might be the start up of this that is
causing you problems, you might try a ceramic resonator.
They are typically less accurate than crystals, but do start a lot faster. Maybe they will also have
a different sensitivity to temperature. Worth a try anyway, if you are getting desperate.

Simon

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2000\08\03@144201 by Matt Bonner

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Tsvetan Usunov wrote:

> Are you sure 150 C ???

Yes.

> I'm interested what PCB laminate you have used for your PCB as FR-4 would
> melt and deformate at temperatures over 130C.

It also deforms at temperatures below that, too, after
enough time.

We don't use FR4 - I'm not sure which material it is, but
it's rated to about 185 degC.  Solder selection is
important, too.  (I do the electronics and firmware - the
production department takes over from there.)

> What type of capacitors (especially electrolyte caps) you have been used?

Tantulum.

> All quartz crystal specs shows up to 70C operation. What happend with them
> at 150C after 1 week operation?

Nope, you can get high temp crystals and oscillators.

> Even don't dare to ask for the connectors, switches and etc. plastics as
> for high temperature the recommended parameters derate down to 10% of the
> normal (for instance the carrying current).

One connector, again Mil rated, no switches or sockets.

All this stuff is *very* expensive, though.

--Matt

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