Re: gEDA-user: Using 60Hz mains frequency for timing?

["David Kerber" <dkerber@xxxxxxxxxxxxxxxxxxxxxxxxxx>]

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: geda-user-bounces@xxxxxxxxxxxxxx 
> [mailto:geda-user-bounces@xxxxxxxxxxxxxx] 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
> 
> 
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