[ntp:questions] GPS_NEMA, but high offset and jitter?

unruh unruh at wormhole.physics.ubc.ca
Fri Feb 26 19:26:14 UTC 2010

On 2010-02-26, David Lord <snews at lordynet.org> wrote:
> David J Taylor wrote:
>>> Is there any other way to watch the signal to see if it's reaching the 
>>> serial port correctly?
>> I would use my 'scope, but even an analogue voltmeter might work - see a 
>> regular flick of the needle.  I built the equivalent of a simple 
>> break-out box into my two connections, one in the RS232 DB-9 plug itself:
> I checked pps from MSF rx with digital meter and that showed a
> signal but not very well. That has a 50ms pulse so 100ms from
> Garmin should be as easy to spot. Analogue meters I have around
> would give a much better indication.
> Another alternative is a transistor + three resistors and
> LED. A pot could be used for R2 to confirm voltage swing
> of PPS output.
>      +5V -- R3 --- LED ---+
>                           |
>                           c
>      pps --- R1 ---+--- b
>                    |      e
>                    R2     |
>                    |      |
>       0V ----------+------+

No need for any of the resistors except R3. but you do not really  need
the transistor, since the PPS line should source enough current to run
the led. Ie, just
PPS ------ R3 ---LED--

should do it, with R3 being about 1K
I would not advise this as a permanant setup but for testing it should
be fine. 


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