[aprssig] Tap into in-dash GPS Navigation for APRS?

Curt, WE7U archer at eskimo.com
Tue Aug 22 11:50:22 CDT 2006

On Tue, 22 Aug 2006, Curt, WE7U wrote:

> On Tue, 22 Aug 2006, Ron McCoy wrote:
> > My understanding is that you can access the GPS signal by breaking into the
> > box but that you have to play with the firmware to change from a proprietary
> > protocol to NEMA, and that breaks the normal OnStar functionality.
> A page I saw mentioned Motorola binary format.  One should be able
> to convert that to something usable with a microprocessor.
> That's assuming it's not like one of the Trimble binary formats
> where the unit has to query the GPS for the data:  In that case
> you'd need to OR the transmit signals from the box and from your
> microprocessor together so either could command the GPS to return a
> position.  A bit of a pain.
> If it's a continuous stream of data from the GPS then you just need
> to tap into the GPS transmit line and convert it.
> Found this, code that switches to NMEA mode for the Motorola:
>     <http://www.kd7lmo.net/beacon_source.html>
> So you could program a PIC to switch the GPS to NMEA mode, get a
> position, then switch it back to Motorola...  Probably better to
> leave it in Motorola mode and just convert to NMEA on the fly
> though.  That way the OnStar wouldn't have a fit.
> This page talks about a PIC-based project to read the Motorola
> binary format:
>     <http://www.pacificsites.com/~brooke/electron.shtml>

"ntpd" sources (Network Time Protocol Daemon) appear to have
motorola binary format decoding as well.  Probably a good set of
sources to learn from.

Curt, WE7U.   APRS Client Comparisons: http://www.eskimo.com/~archer
"Lotto:    A tax on people who are bad at math." -- unknown
"Windows:  Microsoft's tax on computer illiterates." -- WE7U
"The world DOES revolve around me:  I picked the coordinate system!"

More information about the aprssig mailing list