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'[PIC]:18F1320 INTOSC temp stability'
2004\01\03@083116 by Larry Bradley

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I can't find any info in the data sheets about the behaviour of the
internal oscillator of the 18F1320 with respect to temperature.

I'm using the internal osc at 4 mHz for a project, and it appears to be
reasonably accurate - about 0.2 percent at room temperature. The project
involves resetting some counters and computing some averages at midnight
(more or less). My time-of-day clock code can easily be calibrated to
compensate for the error, but I've no idea how the osc freq will change
with temperature. The environment will vary from perhaps 5 degrees Celsius
to 35 degrees Celsius. If the freq doesn't change by too much, I can get
away with using the internal osc, as I don't really need to be too close to
midnight - I can reset the clock manually every few days if necessary.

Does anyone have any ideas as to the oscillator's behavior in this regard?

Larry Bradley
Orleans (Ottawa), Ontario, CANADA

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2004\01\03@084152 by

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Larry Bradley wrote :

> I can't find any info in the data sheets about the behaviour of the
> internal oscillator of the 18F1320 with respect to temperature.

The errate sheet DS80160B has some updated figures
on this matter on page 5.

Jan-Erik.

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2004\01\03@095647 by Olin Lathrop

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Larry Bradley wrote:
> If the freq doesn't
> change by too much, I can get away with using the internal osc, as I
> don't really need to be too close to midnight - I can reset the clock
> manually every few days if necessary.

Is is really worth all that to save a 50 cent crystal?

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2004\01\03@095648 by Larry Bradley

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Yeah, I saw that, but it really doesn't say much. What I was looking for
was something that would say that the osc deviates by x parts per million
per degree temp change, like they do for xtals.

The only reason for not using an xtal is I/O pin count, but I can multiplex
and LCD pin with something else if necessary

At 02:39 PM 1/3/2004 +0100, you wrote:
{Quote hidden}

Larry Bradley
Orleans (Ottawa), Ontario, CANADA

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2004\01\03@100857 by Larry Bradley
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Of course not. It is an interesting experiment, if nothing else. The PICs
have an internal osc - why not use it if it will do what you want? If it
won't, I'll use an xtal - I have a bunch of them. I'd like to use the OSC
pins as I/O ports for this project, but it isn't necessary, since I can
multiplex a couple of other pins if I have to.

At 09:49 AM 1/3/2004 -0500, you wrote:
{Quote hidden}

Larry Bradley
Orleans (Ottawa), Ontario, CANADA

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2004\01\03@101725 by Spehro Pefhany

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At 10:07 AM 1/3/2004 -0500, you wrote:
>Of course not. It is an interesting experiment, if nothing else. The PICs
>have an internal osc - why not use it if it will do what you want? If it
>won't, I'll use an xtal - I have a bunch of them. I'd like to use the OSC
>pins as I/O ports for this project, but it isn't necessary, since I can
>multiplex a couple of other pins if I have to.

Or use a 30 cent resonator with built-in capacitors. A good compromise
for many situations (0.5% accuracy).

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
spam_OUTspeffTakeThisOuTspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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2004\01\03@210208 by William Chops Westfield

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On Saturday, Jan 3, 2004, at 06:49 US/Pacific, Olin Lathrop wrote:
> Is is really worth all that to save a 50 cent crystal?
>
It's more often useful to save two pins.  I've noticed that a lot
of things I contemplate will fit in an 18 pin pic, but NOT one of
the old ones with only 13 IOs.  And of course the 8-pin PICS are a
LOT more useful with 6 I/Os (as atmel found out the hard way...)

> Or use a 30 cent resonator with built-in capacitors. A good compromise
> for many situations (0.5% accuracy).

Where do i get these cheap resonators?  I didn't get any responses
to my last flame to the effect that cheap crystals were far more
common than cheap resonators.  (again, it's an ease-of-use thing.
I want built-in caps! (and how come no one seems to make cystal
modules with built-in caps, anyway?)

BillW

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2004\01\03@215023 by David Schmidt

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Digikey started carrying Murata brand resonators with built in caps.  Under
$0.30/ea in 100's

Dave
> Where do i get these cheap resonators?  I didn't get any responses

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2004\01\03@230952 by William Chops Westfield

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On Saturday, Jan 3, 2004, at 18:49 US/Pacific, David Schmidt wrote:

> Digikey started carrying Murata brand resonators with built in caps.
>   Under $0.30/ea in 100's

And not much more than that even in 1's.  Thanks: it's tough to
keep up with digikey's additions...

BillW

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2004\01\04@020234 by Wouter van Ooijen

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> > Or use a 30 cent resonator with built-in capacitors. A good
> compromise
> > for many situations (0.5% accuracy).
>
> Where do i get these cheap resonators?

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I have 6, 10 and 20 MHz resonators, US$ .36, .36 and .42 each (singles,
pay by PayPal). 0.25 for 25+ (mixing allowed). $8.40 S/H per order. See
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Wouter van Ooijen

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