Generally, if they don't specify a load capacitance, then they are designed
for series operation.  Every crystal has series and parallel resonant
points, but the parameters are only specified for one or the other.  Also,
both can't be on the same frequency.

If you try to pull a series crystal in to operate on the nameplate
frequency in parallel mode, it might work or it might not be reliable..
Hard to say.  I wouldn't do it if I were you.


On Mon, Feb 17, 2014 at 4:31 PM, <lee@baudalign.com> wrote:

> I'm baaaaaaack!  Quick revival, I've been searching high and low for
> appropriate crystals at appropriate prices(!), and the major issue is tha=
t
> most "cheap" ones aren't listing a load capacitance!
>
> Is there any way of determining the load capacitance, or more accurately
> what the appropriate load capacitor values should be?  Or is the "standar=
d
> 22pf caps" "close enough"?
>
> As an example, the cheapest I can source small quantities (5x,10x,50x) of
> a 3225 crystal (or similar size +/- a few mm) with a KNOWN load
> capacitance, is about $1.30 each.  If I source those with UNKNOWN load
> capacitance (and no known brand), then it is more like $0.40 each.
> As an aside, the likes of Digikey/Mouser/Farnell want to charge in the
> order of $30+ to ship a couple of crystals!  RS, on the other hand, have =
a
> local office with free pickup.
>
> I'm primarily doing 8bit sound playback, interrupting @ 16kHz, with some
> I2C to an accelerometer and SPI (or nearly-SPI) to other devices; the
> RS232 comms is primarily for debugging and development, obtaining raw
> accel data for analysis for future function incorporation, so comms
> doesn't need to be the fastest available (code will also be stripped back
> to bare basics at this time).
>
> I do prefer the idea of having an external crystal or resonator, I can't
> remember why off-hand but there was some valid reasoning...
>
> Lee
>
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