[ntp:questions] GPS_NEMA, but high offset and jitter?
David J Taylor
david-taylor at blueyonder.co.uk.invalid
Fri Feb 26 11:10:29 UTC 2010
"David Lord" <snews at lordynet.org> wrote in message
news:7upjodF9s4U1 at mid.individual.net...
> 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 ---+
> pps --- R1 ---+--- b
> | e
> R2 |
> | |
> 0V ----------+------+
On the GPS-18 devices here, I found that an LED and 1K5 resistor alone
were adequate to indicate the PPS signal, and it pulled down the voltage
hardly at all. You could even hand hold the resistor and LED across the
relevant RS232 pins (PPS/DCD and ground). I used a low-current LED for a
Yours is the better way, as it loads the GPS a little less, and I know we
have had discussions about exact signal levels before.
More information about the questions