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PICList Thread
'Crystals vs. Ceramic Resonators'
1996\07\16@232848 by Ed VanderPloeg

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Why use crystals?  To satisfy our anal-retentive personalities which,
though knowing very well that the customer will never notice his 60 second
delay taking 60.3 seconds, still forces us to shoot for 60.0 seconds.

Oh, and there's the detail about async communication baud rate generation.
If the PIC already generates something on the fringe of the timing
tolerance, then the ceramic resonator's possible errors could push it over
the brink.  Sure, you could pick a frequency that divides nicely to the
desired rate, but for a few cents more it's something I'd rather not even
worry about.

Ceramic Resonator error stack up:
0.5%(nominal tol) + 0.3%(temperature) + 0.5%(aging) = 1.3%

Crystal error stack up:
50ppm(nominal tol) + 100ppm(temperature) + 50ppm(aging) = 200ppm = 0.02%

For communication based designs or those with accurate timing requirements
I'd still go with a crystal but the rest get a ceramic resonator.  Unless
of course those Panasonic resonators have a total error stack up of under
0.5%, then I'll reconsider.

-Ed V.


______________________________ Reply Separator _________________________________
Subject: Re: PIC Crystals
Author:  spam_OUTfastfwdTakeThisOuTspamix.netcom.com at InterNet
Date:    7/16/96 7:40 PM


John Piccirillo <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU> wrote:

> what kind of crystal should I use.  Catalogs list microprocessor
> crystals, besides frequency, as TTL or CMOS levels, and loads as
> "series" or for a particular capacitance, eg. 20 pf. Does it make
> a difference and do I use external capacitors?  I have the PIC Data
> Book but don't recall it specifying details about the crystal.

John:

It does make a difference, and you should be using a parallel crystal
with external capacitors.  The Data Book actually does say this, but
you have to read the whole section to find the information.

I don't really understand, actually, why so many people on the list
are using crystals at all.  Ceramic resonators are accurate to within
0.5% or so, and they're easier, cheaper, and (if you buy them with
internal capacitors) smaller than crystals.  Panasonic resonators
with built-in capacitors are available from all the major catalog
distributors.

-Andy

Andrew Warren - fastfwdspamKILLspamix.netcom.com
Fast Forward Engineering, Vista, California
http://www.geocities.com/SiliconValley/2499

1996\07\16@235128 by Clyde Smith-Stubbs

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evanderploeg@creo.bc.ca wrote:

> Why use crystals?  To satisfy our anal-retentive personalities which,
> though knowing very well that the customer will never notice his 60 second
> delay taking 60.3 seconds, still forces us to shoot for 60.0 seconds.

And anyway, the price difference between a crystal and a resonator can't
be more than about 50 cents - we pay the equivalent of about US$0.70 for
a crystal - I don't know what a resonator is worth, but I can't see it
being less than 20 cents.

--
Clyde Smith-Stubbs       | HI-TECH Software,       | Voice: +61 7 3300 5011
.....clydeKILLspamspam.....hitech.com.au      | P.O. Box 103, Alderley, | Fax:   +61 7 3300 5246
http://www.hitech.com.au | QLD, 4051, AUSTRALIA.   | BBS:   +61 7 3300 5235
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For info on the World's best C cross compilers for embedded systems, point
your WWW browser at http://www.hitech.com.au, or email EraseMEinfospam_OUTspamTakeThisOuThitech.com.au

1996\07\17@034119 by fastfwd

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Clyde Smith-Stubbs <PICLISTspamspam_OUTMITVMA.MIT.EDU> wrote:

> And anyway, the price difference between a crystal and a resonator
> can't be more than about 50 cents - we pay the equivalent of about
> US$0.70 for a crystal - I don't know what a resonator is worth, but
> I can't see it being less than 20 cents.

Clyde:

You're very close; the last time I ordered $ MHz resonators in large
(>100K) quantities, they cost 18 cents apiece.

For some of us, a 50-cent price difference is HUGE.  I suppose the
cost doesn't make a difference to everyone, but resonators are also
(as I said) smaller and easier to use (have you seen ANY questions
on the list regarding resonators that won't oscillate?).

-Andy

Andrew Warren - @spam@fastfwdKILLspamspamix.netcom.com
Fast Forward Engineering, Vista, California
http://www.geocities.com/SiliconValley/2499

1996\07\17@040413 by fastfwd

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   I wrote:

> .... the last time I ordered $ MHz resonators ....

   That should have been "the last time I ordered 4 MHz
   resonators".

   Sorry.

   -Andy

Andrew Warren - KILLspamfastfwdKILLspamspamix.netcom.com
Fast Forward Engineering, Vista, California
http://www.geocities.com/SiliconValley/2499

1996\07\17@091242 by Mark K Sullivan

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And don't try to synthesize DTMF or other precise audio tones from a resonator.

- Mark Sullivan -

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