[ntp:questions] NMEA ref.clock better than my ISP's timeserver?
David J Taylor
david-taylor at blueyonder.not-this-part.nor-this.co.uk.invalid
Fri Jun 12 10:50:17 UTC 2009
David Lord wrote:
> First I don't think there's any problem getting the nmea down
> twisted pair at 4800 baud.
.. agreed, but .....
> To play safe with the ttl level pps I've setup to use a simple
> emitter follower that can drive into 75r coax.
> I didn't want to use line drivers as I don't have any handy that
> work off single 5V supply.
> I need a converter back to ttl before going to pc and don't have
> any spare gates in the box with compulsory flashing led and
> ticker, so will use another couple of transistors wired as
> Schmitt trigger.
I think you're needlessly overcomplicating the PPS signal. I have the GPS
18LVC feeding /two/ parallel RS-232 interfaces, /and/ a low-current LED,
so for a 30m length I think you would get away with a simple wire
connection. However, have fun with the soldering iron!
If you're seeing 4us offset now, that may be as good as it gets. You may
need a more constant temperature to see better.
More information about the questions