[aprssig] Nuvi and APRS

Scott Miller scott at opentrac.org
Tue Mar 25 02:06:23 EDT 2008

> See the Tracker 2 www.argentdata.com  It is able to make use of the 
> Nuvi's FMI. However, waypoint upload only works properly so far for the 
> Nuvi 350. The other models create a new waypoint every time a station 
> moves rather than updatiing the position. It is hoped that Garmin will 
> provide an update for the other models.

Right.  At this point, it probably wouldn't hurt for T2 users with other 
models to start dropping polite notes to Garmin tech support about this. 
  They understand the issue, but it's not a priority for them.  I don't 
want to annoy anyone, but I do want them to know that a minor firmware 
change would make a lot of users happy.

>> I received a Nuvi as a present and  would like to interface it to my
>> THD700.  I have already downloaded the developers kit but am really
>> hoping work was proceeding on this already.
> I don't think there is any way of interfacing it with anything on the 
> APRS scene other than the Tracker 2.

Right again.  I'm not aware of any other non-PC APRS device (or any APRS 
software client, for that matter) that supports the Garmin binary 
protocol at all.

It's definitely a non-trivial thing for a small microcontroller.  For 
example, rather than giving course and speed for velocity, it gives 
separate X, Y, and Z velocities, in floating point format.  Getting 
course and speed requires a bit of math and a floating point emulation 
library - that's why the OpenTracker+ will never support it; there's 
just no room.  Even for the T2 I had to write my own arctangent function.

As I've said before, I don't expect Kenwood to tackle it any time soon. 
  The Garmin protocol is too poorly documented in the parts that are 
vital to APRS use, and it's a moving target - things change with 
firmware updates to various models.  Kenwood has never shown any 
interest in user-upgradeable firmware, and that's going to be almost a 
necessity for Garmin compatibility.

>> Also could some one tell me if there is a standard for USB cables?
>> It seems that every USB device I have has a different connector on
>> the cable.
> Perhaps the following page will be useful... 
> http://en.wikipedia.org/wiki/Usb
> Also... www.usb.org/developers/docs/

Keep in mind that the Garmin fleet management interface does NOT use 
USB.  Hook it up to a USB host, and it goes into mass storage device 
mode.  You've got to pull the unnamed (and normally unused) pin on the 
mini-B connector to ground through an 8.2k resistor to put it into an 
RS-232 compatible serial mode.

I could make a protocol translator that'd let the D7/700/710 use the 
Nuvi like any other GPS, getting position data and (if supported) 
sending waypoints, but it wouldn't do anything interesting like text 
messaging.  At this point, I don't think it's worth the trouble.


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