AVR-Chat

Yes, its a challenge.

After frequency, the next thing is "series or parallel".
The normal processor crystal oscillator with two caps
(whether external or not) is a "parallel". The ONLY
difference in the crystals is the way the crystal is
calibrated. If you choose the wrong one, it will be just be
off in frequency a little. Not by much, though!

After that, it is choosing for the appropriate capacitance.
If the circuit uses two 22pf caps, the EFFECTIVE
capacitance is 1/2 the value of an individual cap (11 pf in
this example) plus the stray capacitance of the processor
pins, etc. I've been told thats about 7pf. 

After that, it comes down to size and cost and maybe
tolerance accuracy. Throw a dart and see which one is
closest!

Jim Wagner

On Wed, 15 Dec 2004 10:45:34 -0800
 James Washer <washer@trlp.com> wrote:
> 
> When I look through my DigiKey catalog, I see a
> bewildering choice of crystals. Picking the
> "speed" is easy, but how do I choose amongst
> the different "series", and type? 
> 
>  - jim
> 
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