[aprssig] Garmin C550 GPS

J. Lance Cotton joe at lightningflash.net
Thu Dec 4 11:27:21 CST 2008

On Thu, Dec 4, 2008 at 10:51 AM,  <joe at dellabarba.com> wrote:
> I am getting a C550 GPS from Garmin. For $150 +/- on closeout it is pretty good - it does GPS, MP3s, FM traffic data, and bluetooth hands free. I noticed it has an optional "fleet management" cable. Is it possible to extract NMEA from this for APRS use? Can it do anything else useful?

A special FMI cable puts these device into fleet management mode,
which causes some pins on the mini-usb connector to become
Garmin-protocol interface in RS-232 mode. Garmin protocol is a binary
protocol, but Scott Miller's (N1VG) Tracker 2 device supports Garmin
mode data. On the plus side, the Tracker2 also makes use of this fleet
management mode to enable easy sending of messages to other APRS users
as well as configuration of the Tracker2 from the GPS's touchscreen.

Various models of Garmins have differing quality of implementation of
the FMI mode and I don't know if anyone has tested the C550 with the
Tracker2 to find out how well it performs. I think it's generally
accepted over on the Tracker2 mailing list that the Nuvi 350 has the
best implementation of FMI for use with the Tracker2; that device is
now discontinued.

Scott also recently posted a note on his work towards deciphering the
FMI v2 protocol, which presents many challenges. I don't know which
version of FMI the C550 offers, but since it's on closeout, it is
likely a older model with FMI v1, which works.

I don't recall, but it's also possible Scott is working on a simple
garmin-protocol -> NMEA translator circuit that doesn't bother with
all the FMI features, but just does plain translation.

I'm sure Scott will pipe in later on this as well.

-Lance KJ5O

J. Lance Cotton, KJ5O
joe at lightningflash.net
Three Step Plan: 1. Take over the world. 2. Get a lot of cookies. 3.
Eat the cookies.

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