Like others said, the 60Hz frequency is accurately controlled to a few cycles per DAY, so long-interval low-resolution (8.3 ms period) timing may be more accurate using that, while short period, or higher-resolution timing would be better handled with your crystal.
> -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Randall Nortman > Sent: Friday, May 02, 2008 12:33 PM > To: gEDA user mailing list > Subject: gEDA-user: Using 60Hz mains frequency for timing? > > Just a quick non-gEDA design question -- I have the choice > between using the zero crossings of the 60Hz mains voltage or > my MCU clock (generated from an 18.432MHz quartz crystal > producing a 48MHz CPU clock via PLL built into the MCU) for > low-resolution timing. The crystal is not designed as a > watch crystal, so its tolerance is probably pretty poor, and > furthermore this board will see wide temperature swings, > which I think has an affect on the crystal frequency as well. > I have no idea how precise the 60Hz line frequency from the > power utility is, but it at least is probably not > temperature-dependant. Either one is easy to use -- I just > want to be as accurate as possible. > > Anybody have suggestions? TIA, > > -- > Randall > > > _______________________________________________ > geda-user mailing list > geda-user@moria.seul.org > http://www.seul.org/cgi-bin/mailman/listinfo/geda-user > _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user