Re: "What time is it?" aksed the microcontroller

From: Richard (rh86_at_azglobal.com)
Date: 05/23/04 

Date: Sun, 23 May 2004 10:07:44 -0700

Paul Keinanen wrote:
> If only synchronised time but not absolute time is
> needed and all devices are connected to the same
> synchronised national/continental AC power grid,
> it can be used to generate a common clock signal
> to all devices.

Interesting thought, once the initial sync can be achieved. SOme
thoughts on this...

The power grid clock is not constant (it varies +/- throughout the day),
but probably isn't adjusted at a rate that would cause problems for this
approach. However, I understand that grids are often inter-linked with
DC, so it may work in some areas but not others.

It all depends on the timing accuracy required. And I wonder how well
it'd work behind UPS systems - many operate with batteries "on-line"
(power is rectified, then re-alternated), so the output may not be
sync'd with the grid.

> Also the field and line sync pulses from a local
> TV-transmitter (or TV satellite) has been used in
> the past to synchronise receivers far apart

Good point. Even with digital TV, there's bound to be a timing signal
you could sync from. Cellular would be another option.