[time-nuts] Logging the grid frequency....

[Chris Albertson]

On Fri, Feb 22, 2013 at 10:47 AM, Hal Murray <hmurray at megapathdsl.net> wrote:
>


> You can also feed the line into a modem control signal on a PC serial port.
> (USB probably won't work.)  The PPS logic from NTP will count cycles and
> record a timestamp on the last one.

Yes RS-232 wants a signal that is about +/- 9 volts. so if you are
very brave all you need is a 15:1 voltage divider on the AC to scale
it.  However it is smarter to use a transformer.     Some others who
are even more conservative were using an optocoupler between the AC
mains and the PC's serial port. But I think the transformer provides
good enough isolation.


>
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-- 

Chris Albertson
Redondo Beach, California