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

[Michael Stovenour <mstovenour@xxxxxxxxx>]

Why not just use one of these:

Analog Devices ADE7753 - Has an application note AN564 with a complete design.  There is also an evaluation board w/ schematic ADE7753EB



----- Original Message ----
From: Randall Nortman <geda-lists@xxxxxxxxxxxxxxx>
To: gEDA user mailing list <geda-user@xxxxxxxxxxxxxx>
Sent: Friday, May 2, 2008 1:21:32 PM
Subject: Re: gEDA-user: Using 60Hz mains frequency for timing?

Thanks very much to all who responded... and so quickly.  I should
have included more information on the application -- This is for
building a power meter (watts and watt-hr) for measuring power
consumption of particular circuits as well as the whole house (but not
for billing purposes -- just informational).  To give you an idea of
what I mean by "low resolution", The timing will affect primarily the
watts output, which is calculated as 15-second averages.  It is also
somewhat important that the watt-hr accumulation correlate with the
*monthly* energy bill, which comes from the utility's meter on the
outside of the house.  I am sure that older electromechanical meters
rely on the 60Hz signal for timing; I'm not sure what newer digital
ones do.

It sounds to me like my 15-second periods will perhaps be slightly
more stable with the crystal, but the 60Hz should get close enough.
For the monthly comparison with the utility power meter, it sounds
like the long-term stability of the 60Hz is likely to be far better.
I get either signal for "free" already (with good glitch filtering on
the zero-crossing detect), so neither is more convenient.  Given all
that, I think I will go for the 60Hz signal.  Or maybe if I have some
spare time I'll test one against the other -- assume the 60Hz is
stable on a daily basis and check the drift of the crystal against it.

Thanks for all the info.

-- 
Randall


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