[time-nuts] Trimble Thunderbolt 1pps

[Chris Albertson]

The TTL level PPS did not work for me when I tried to drive a long cable.
 I used the MAX232 level converter chip to level shift.

Do check the polarity.  If you get it wrong it will appear to work but the
timing will biased by the pulse width. (the falling edges is used if you
get it wrong.   RS-232 levels are backwards from TTL except control
signals.   Just be sure you have the "correct" number of inverter.  Then
when you are done check the time is right.

Being off by the pulse width in itself may not be bad because you can
compensate in the software with a "fudge" parameter in the .conf file.
But I wonder if the pulse width is well controlled.  Do they use a one-shot
or an RC circuit?  Or do they count clock cycles based on the 10MHz clock?
   I don't know, safer to just use the leading edge.


On Fri, Jan 3, 2014 at 11:30 AM, Hal Murray <hmurray at megapathdsl.net> wrote:

> > Does the Trimble Thunderbolt provide 1pps on DCD of the RS232 interface?
>
> No, but you can open it up and add a wire.  That will give you CMOS rather
> than RS232, but it works.  (Or at least, it works for me and I've never
> heard
> a good story where it didn't work.)
>
> One problem is that the PPS signal is narrow.  Some PCs may not be able to
> catch it.  You can use the FatPPS from TAPR:
>   http://www.tapr.org/kits_fatpps.html
> (It needs power.  You can probably find that in the TBolt.  I haven't done
> it.)
>
> I added a diode and R/C.  That was good enough for the PC I was using.
>
>
> --
> These are my opinions.  I hate spam.
>
>
>
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-- 

Chris Albertson
Redondo Beach, California