On Tue, 15 Jul 2008 10:29:00 -0700, Josh Assing
wrote:

When I got my second nmea device, i was excited -- "hook it up" the manual said
-- support said "yes; you just hook up all the nmea out with nmea in of the
other devices and visa versa" so I did.

It appeared to work. however, since I have some weird things recently
discovered, we've traced it down to the fact that the info I got was wrong; and
my understanding of nmea was woefully weak.

GPS: listens & talks (2 lines of each)
RADAR: listens & talks
navtex: listens only
autopilot: listens only
flowscan: listens only
VHF listen/talk

Navtex, Autopilot & flowscan need to listen to the gps
radar & gps need to listen & talk to each other
The VHF radio talks/listens to the gps.

AIS receiver is in the budget & will need to talk to the gps & radar.

From a few hours search; it seems I need multiple-multiplexers to make this work
"correctly" -- can anyone give me a hand?

-josh

One Very Important Rule: you can only have _one_ "talker" on an NMEA
circuit, but can have several listeners. It looks like you will need
a multiplexer to combine the GPS, Radar and VHF output data into one
talker feed that everything listens to. (but you may have problems if
something repeats everything it hears, as well as sending its own data
- there are some intelligent muxes that can filter data to prevent
this causing a problem)

Note that normal NMEA-0183 data is sent at 4800 baud, while AIS data
is normally sent at 38400 baud - they can't coexist on the same
circuit. My Raymarine C80 chartplotter/radar display can accept AIS
data at 38400 on its serial port, while the GPS and other NMEA-0183
data goes into the SeaTalk system via a Raymarine NMEA=SeaTalk
interface box.

--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca