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Subject: Re: Radio Synchronized Clock
From: Dov Kruger (dkruger@XXX.XXX)
Date: Thu Feb 28 2002 - 10:54:12 EST
Brian Whatcott wrote:
> the radio clock module was on offer at $24 (year 2000 prices).
You don't even need to keep it connected if you are willing to bring it
up to where it can receive a signal and synchronize it every so often.
Another idea, and one that has been implemented by amateur radio
enthusiasts, is to build (or buy) a digital clock module and govern it
with something more accurate, like a GPS.
They are much more sophisticated than I wanted. My idea for a simple but
highly accurate chronometer was to assume that any error is due to a
slightly mis-sized crystal, and therefore to correct it at a constant
rate. Since the things tick 32768 times a second, you simply count the
pulses and every n add or subtract one from the count. Two levels of
counter would correct the inherent error in the device, giving you a
very accurate clock. My hope is that someone implements this in a
wristwatch, because given that it sits on your wrist, I am willing to
bet the next biggest source of error (temperature) will be near zero as
your body heat stabilizes the watch. But for a more robust device, you
need an integrated thermometer so you can correct differently as the
temperature changes.
If you want to see devices and kits out there that you can buy, just
search google for "digital clock kit accuracy" and you'll get plenty of
hits. For a couple of hundred, you can build a kit, connect it to an old
GPS (all it needs is the timebase from the satellites), and then it can
sit below, getting data from the antenna on deck.
cheers,
Dov
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