[aprssig] APRS and Garmin Nuvi

Scott Miller scott at opentrac.org
Thu Jan 31 23:00:40 EST 2008

I discovered something interesting today.  Here I've been telling people 
all along that the newer USB-only Garmin receivers like the Nuvi are 
worthless for APRS.  Turns out I was wrong.

When I heard about Garmin's fleet management interface, I decided it'd 
be worth checking out.  It needs a special cable, though - for the Nuvi 
350 I picked up, it's Garmin p/n 010-10813-00.  By the looks of it, it's 
probably just got a level converter inside, but I'm not sure. 
Apparently there's a serial interface of some sort that can share the 
USB connector.

The fleet management protocol looked suspiciously like a subset of 
Garmin's regular binary serial protocol, so (once I figured out the 
cable pinouts and soldered on a DB9) I fired up the test program I'd 
written, and sure enough, it spit out a list of supported protocols.

I plugged it straight into a stock Tracker2 and the activity light 
started blinking green, showing a good fix.  I piped in some recorded 
APRS traffic and the map screen started showing APRS stations.  Here are 
some pictures I took (haven't tried the screen capture program yet):

Map screen (2D mode): http://n1vg.net/images/nuvi-map.jpg
Waypoint list: http://n1vg.net/images/nuvi-list.jpg
Station detail: http://n1vg.net/images/nuvi-detail.jpg

It's not perfect - the waypoint set is different, for one.  You can see 
that all of the cars are now up on lifts with the hood up!  The digis do 
show up as antenna towers, at least, and the houses are there.  I'll 
have to find out if it'll take custom symbols.  Also, it seems to have 
some quirks about showing waypoints at different zoom levels.

The Nuvi 350 has a USB port on the side and another one on the clip-on 
base, so you can power it and plug it in to the tracker at the same 
time.  When I find out how the serial interface adapter works, I'll see 
if I can power it from the tracker, or maybe vice versa.  I'll also see 
about a cheaper substitute for the cable - this one cost me $30 after 
shipping.  It probably wouldn't be hard to build an equivalent circuit 
into a DB9 shell.

The bad news is that the Tracker2 (at least the OT2m version) is totally 
sold out right now.  My only two spares are going out for CE EMC 
certification shortly.  The factory producing the boards is snowed in 
right now and hasn't even been able to get the parts for the next batch 
- DHL's had them sitting at the depot for days.  It'll probably be the 
end of February before I have any more.  The T2-135 (for the Alinco 
DR-135) is shipping, albeit slowly due to limited production capability 
here.  (The Tracker2 page has moved to 
http://www.argentdata.com/products/tracker2.html if you're looking for 
more information.)

Hopefully by the time the boards come in I'll have figured out all of 
the Nuvi's quirks and dealt with them.  I also hope to make some use of 
the fleet management interface for some new features.  Most importantly 
- it does text messaging.


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