[time-nuts] Re: UTC, 60 Hz

Poul-Henning Kamp phk at phk.freebsd.dk
Thu Jul 28 02:38:18 EDT 2005

In message <002d01c5933c$6c1d2f60$8e18f204 at computer>, "Tom Van Baak" writes:

>You know, if the stackable TAPR module
>project catches on another PCB on the list
>could be a mains frequency monitor.
>It would robustly filter and divide the 50/60 Hz
>mains frequency to 1 PPS and then onboard
>compare that 1 PPS against the local (OCXO,
>atomic, or GPS) 1 PPS to a modest precision
>(say, 1 or 10 us).

I actually wrote one in a Z80 many years ago: It would
measure the period of 50 mains cycles (ie: 1 second)
calculate the reciprocal and display frequency with
4 decimals.

Do it on a PIC18F* and feed it a 10MHz atomic clock
and you are done.

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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