AVR-Chat

Dave VanHorn wrote:
>>I have wondered just how important the associated capacitors are for accuracy?
> 
> 
> Bing, pet peeve button pressed.. :)
> http://www.dvanhorn.org/Micros/All/Crystals.php

Hi Dave!

I've read your web page(s) and like your discussion not only on xtals
but also bypassing.  Interesting.  And if anyone reading this wants to
know a little about bar-decoding, Dave's website is a good resource.

I have a project where I need to be able to adjust the crystal frequency
to a specific "exact" value.  I haven't breadboarded it yet, but do you
have any experience or advice along this line?  My thought was to just
make one of the crystal caps variable (make any difference which one?).
 For example, using a 10 MHz xtal, I wish to be able to zero beat WWV.
(Long term stability not too important, so it would not be ovenized or
otherwise temp-compensated.)

I'm not too sure how close the cheap microcontroller crystals are to
their specified frequency either -- imagine that would depend on
manufacturer, lot, etc.  In my application some selection would be
acceptable rather than go to closer tolerance xtals.

Other than parts count and cost, do you see any downside to using the
microcontroller's oscillator in this manner versus using a separate
crystal oscillator (with transistor) driving the microcontroller?

Don