[aprssig] DigiTraveller questions

Wes Johnston aprs at kd4rdb.com
Mon Oct 11 13:12:50 CDT 2004

Any voltage on pin 3 (tx data in to GPS) will cause it to turn on.  Removing
that voltage causes the GPS to turn off in 3 or 4 seconds.  If you wire pin 3
to any switched power source in your car, you can leave 12v (ie 5v with a 7805)
on the GPS all the time.  You may want to clamp the pin 3 input with a 5.1 or
12v ziener diode and resistor... but hey, rs232 is rated +/-12v with a 3000 ohm
input impedance... YMMV.

If you leave power on the GPS or leave batteries in it, the time to fix is
usually 30 seconds or less.  Without power it is usualy 90 sec to 3min.  One
small problem with batteries... the gps draws 3ma when powered down. AAA
batteries will last about 2 weeks like this and then the GPS will get confused
and not start when power is applied.  If you pull the batteries and cycle power
it will start in 90 seconds.  I think this is caused by a disparity between the
BB Ram failing and the GPS low voltage dropout not failing at the same
voltage... ie the BB ram has forgotten all gps data, and the GPS expects to
read data from it.. and it ain't thar to get.


Quoting Earl Needham <needhame1 at plateautel.net>:

> At 10:23 AM 10/11/2004, Wes Johnston wrote:
> >No word on active antenna
> >
> >wiring:http://www.grundlgasse.at/thomas/digitraveler/
>          Thanks, Wes!
>          I am thinking of an active antenna because of the LOOOOOONG time
> it takes to acquire a fix.  Might help, might not, but I'm considering it.
>          7 3
>          Earl
> Earl Needham, KD5XB, Clovis, New Mexico  DM84jk
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