[ntp:questions] OT: GPS18x LVC failure

David J Taylor david-taylor at blueyonder.not-this-part.nor-this.co.uk.invalid
Mon Oct 12 10:15:30 UTC 2009

"David Lord" <> wrote in message 
news:7jgd8oF35kvmbU1 at mid.individual.net...
> David J Taylor wrote:
>> If the Garmin can deliver +/-5V, it should certainly drive almost any 
>> reasonable RS-232 port.  It sounds as if your USB converter has a lower
> I doubt now that I tried with the Garmin on the server (possibly
> tried on eeepc but not yet sorted the data). I'd had <165us at 50%
> from MSF/SHM/PPS via serial, then just after that noted failure
> to get useful result via usb-serial, no better than 10ms. I don't
> have figures handy for MSF without PPS via serial. Outputs for
> MSF/DCF77 are current sinks to 0V, Conrad pulldown for MSF and a
> BC337 on my PPS module.
> David

It seems odd that the GPS18x has "near RS-232" levels on the TX data, but 
not the PPS/DCD line.  Perhaps it's just that line which needs a boost? 
I've driven a few mA into an LED direct from the PPS line, so perhaps it's 
more pulled up to +5V (current limited) than a current pull-down to 0V 
(which should be towards -5V/-12V in any case).


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