There are essentially three methods to obtain the US atomic clock time:

User input (unreliable)
Wired
Wireless

We'll assume that user input is not appropiate for your needs (which we
don't know since you didn't tell us the required accuracy and frequency
of update).

Wired options are:
Phone to atomic clock (requires modem, accurate to the delay of the
phone network)
Phone to internet, get time from atomic clock (requires modem, internet
connection, accurate to the delay of the internet, but can be
compensated for significantly)
Ethernet to internet, get time as above(requires ethernet internet
connection, broadband internet account of sharing of dialup from PC on
premise, accurate to delay of internet, but can again be compensated for)

Wireless options are:
WWVB (Requires low power radio receiver and simple decoding.  Accurate
to several milliseconds, depending on decoding hardware.  Could be
accurate to microseconds with better radio and decoding hardware)
GPS/GLOSNASS(sp?) (requires Global position radio (american, russian,
mix), and clear view of sky.  Accurate to milliseconds depending on
radio, and can be accurate to microseconds and better)

The lowest cost option is likely to be the WWVB signal.  It's trivially
simple to receive (though gets more complex if you want to receive it
*well*), and can be decoded by the microcontroller fairly easily.  The
signal can be received through buildings depending on the antenna and radio.

-Adam


Tony Pan wrote:

>Hi,
>
>I really need to design a product that knows the official U.S. time, aside
>from other features. Can someone tell me what is required for the hardware
>and software to acquire the official time? And what kind of connections are
>required?
>
>Thanks a lot!
>
>Tony
>
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