[ntp:questions] OT: GPS18x LVC failure

Unruh unruh-spam at physics.ubc.ca
Mon Oct 12 16:59:51 UTC 2009


"David J Taylor" <david-taylor at blueyonder.not-this-part.nor-this.co.uk.invalid> writes:

>"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).

Run the pps into the printer port interrupt instead. I think the interrupt handler
is better anyway.
(Of course if you have no parallel port this is difficult)




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