Hal Murray wrote:
I was thinking of modifying my Tbolt to put the 1 PPS on one of the unused
RS-232 leads. It just seems like it would be really convenient to have
that signal available to import into a computer.
NTP expects the PPS signal on pin 1, DCD.
It looks like it's not going to be quite as simple as I'd hoped. So before
I reinvent the wheel, has anyone done this mod and could you offer any
suggestions or warnings?
What's not simple about it?
I just turned the board over and ran a wire from the BNC pin over to pin 1 on
the RS-232 connector. It wasn't connected to anything. (There may have been
a trace, but it went to an empty pad.)
The problem for me was that the PPS pulse wasn't wide enough for one of my
PCs to catch. (Another one does catch it.)
I changed the wire into a diode, resistor, and cap. It's a kludge, but it
works.
Problem 1: As you found, the pulse was too narrow. I was thinking
about doing something very similar to your idea.
Problem 2: Because you connected the TTL-level 1 PPS to the RS-232, you
may find that not all computers will recognize it. A computer that
actually followed the RS-232 rules wouldn't see it at all. I don't know
if any modern computer actually follows those rules.
Problem 3: The fix to Problem 2 is to use the spare converter in the
TTL / RS-232 converter chip. However, it already has data on it that
goes absolutely nowhere so which trace should I cut to free the input
without affecting anything else?
Problem 4: Who knows? That's why I'm asking.
Ed
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