[time-nuts] WWVB PPS clock pulse ?

Chris Albertson albertson.chris at gmail.com
Mon Mar 28 18:36:10 UTC 2011


On Mon, Mar 28, 2011 at 9:46 AM, Lenny Story <lenny at codematic.com> wrote:

> Or can I do a rising edge PPs pulse that's active for 10ms then lowers ?

Yes.  It's the leading edge that matters but 10ms is more of a spike
than a pulse.  It should be longer, maybe at least 10X longer.  It
should be something easy enough to notice even on a DMM.

There is a question about polarity and voltages.  The RS232 standard
has data inverted from what TTL uses with a 1 being negative  but
RS232 does not invert control signals  So the PPS if gong into a
serial port is not inverted.   But the common ttl->rs232 level
converter chip inverts the signals o you need to invert the control
signals before level shifting.  Not  rocket science just a need to be
careful.   Now, if your pulse is long enough to be seen by eye you can
verify by eye you are doing the conversion correctly.

If you get it wrong then the computer sees what you thought was the
trailing edge as the raising edge.  A long 200ms pulse makes this
error easier to see.

-- 
=====
Chris Albertson
Redondo Beach, California



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