Capacitor for crystal

On Sat, 09 Aug 2008 19:32:53 +0530, the renowned ClueLess



The resistor is there to limit drive power.. so it depends on crystal
characteristics (ESR, max drive power) and other things (drive
voltage, load caps). It's not a straightforward calculation,
particularly if you want to minimize power consumption and/or drive
power. Overdriving the crystal can lead to excessive drift or failure.
Typically 32kHz-ish crystals have *maximum* drive powers in the 1uW to
100nW range.


Best regards,
Spehro Pefhany

On Sat, 09 Aug 2008 10:59:14 -0400, Spehro Pefhany


crystal


Thanks for your response.

Actually the micro is running slower, say about 5%, than what it should (a
thirty second operation takes place in 31.5 seconds) so I was wondering whether
the RC values have any bearing.

Perhaps I should try to change the C value by inserting a trimmer instead of the
fixed cap.

Thanks again for your time and help

it sounds like the intended operation is running slower than expected rather
than the crystal itself. if you can't measure the crystal frequency assume
it is close enough and adjust your timing withing the routine via software.
off the top of my head, adding C to the circuit will probably slow it
further... j