[ntp:questions] Convert PPS signal from BNC to RS-232!

John Ackermann N8UR jra at febo.com
Thu Mar 1 14:45:05 UTC 2007

If the signal on the BNC connector is at TTL levels (0 and 5 volts), the 
odds are very good that you can hook it directly to the DCD line on the 
serial connector.  Virtually all serial ports today will work with TTL 
level signals.

The other issue that may be of concern is the width of the pulse.  Some 
clocks have a very short pulse that's only 20 microseconds or so long. 
That is too short for a serial port to reliably read.  A pulse stretcher 
can solve that problem.


Jon Kåre Hellan wrote:
> Erling Paulsen <erling at bee.cc.uit.no> writes:
>> Hello.
>> I have a Symmetricom Syncserver S250 as primary NTP-server. 
>> This box has PPS-output via a BNC connector. I need to get this PPS signal 
>> onto a rs232 connector.
>> Are there any converter kits that can do this, or do I need to make my own 
>> "box" for doing this? 
>> I have setup a secondary server (ntpd on FreeBSD) that will use PPS to 
>> discipline its clock via /dev/pps (on a serial com-port).
>> Any hints on how to get the PPS from the BNC(coax)-output on the primary 
>> server to the com-port on the secondary server would be appreciated. 
> I have seen many designs. One is at
> www.kernel.org/pub/linux/daemons/ntp/PPS/TTLtoRS232.ps.gz and uses a
> CA3140E op-amt. Another is at
> http://www.eecis.udel.edu/~mills/ntp/html/pps.html, but dated
> 1992. You can also use a MAX232.
> Hope this helps.
> Jon Kåre
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