[time-nuts] Thunderbolt PPS Modification

Hal Murray hmurray at megapathdsl.net
Sun Sep 26 00:01:18 UTC 2010

> 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 

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