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


I have had exactly the same problem with (almost) exactly the same stuff
you have. Multiplexers did not fit the bill for me since their inputs
are usually limited to 4800bps while many NMEA sentences (like HDT)
should be transmitted much more frequently. In the end I managed by
intelligently coupling the nmea i/o ports on all my devices (most of my
devices have multiple NMEA in and out) and for the few connections I
couldn't 'fit' I wrote a WIN32 based program for the navigation computer
that combined the input from a few serial-USB converters into one serial
38k4 stream.
In any case, if you decide to go for NMEA multiplexers make sure they
support the speed you require.