[ntp:questions] Using Trimble TSIP under Linux
nomail at example.com
Mon Oct 29 08:38:04 UTC 2012
David Taylor <david-taylor at blueyonder.co.uk.invalid> wrote:
> - use sudo ppstest /dev/pps0 and see assert pulses coming in
> (the clear field is always 0 though, perhaps the 150
> microsecond pulse is too narrow?)
That is a problem!
Now I remember...
I tried different GPS receivers when writing the code for the PPS
support in gpsd, and there was a receiver for which it would not
work because the pulse is too narrow for the technique used in gpsd.
It was the Trimble, I remember now.
You need to add a circuit to stretch the narrow pulse into a 100ms
pulse. The exact duration is not important. Just arrange for a
monostable multivibrator that gets triggered by the rising edge
of the pulse and extends the pulse by R/C time. Make sure the pulse
is shorter than 500ms or the autodetection logic will focus on the
wrong edge of the pulse.
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