Each NMEA circuit can have only ONE talker. NMEA 0185 is too simple
and talkers are too stupid to listen before they start sending data to
listeners....unfortunately.
As you only have ONE talker on your circuit, it's fine the way it is.
You only need a multiplexer if you have to have more than one talker
talking simultaneously. What the multiplexer does is to store all the
talkers' data from several talkers (ours has 4 inputs), then send out
each NMEA statement, in rotation, to all the listeners connected to
its output. This keeps the multiple talkers from crashing into each
other. In our 4 port multiplexer you get:
DATA 1 THEN DATA 2 THEN DATA3 THEN DATA4 THEN DATA 1 and it keeps
repeating as long as its on. The listeners are bombarded with
statements from them all continuously, but "in line".
Now there's something else to think about. What if one of my talkers
is a Garmin 185 GPS sending out GPS data.....and my Raymarine
radar/chart plotter's separate WAAS-GPS receiver to steer the chart
plugs in the radar is ALSO sending out CONFLICTING GPS information.
It's much more accurate than the Garmin is uncompensated with its
satellite-corrected WAAS receiver. What would happen if this data
went to The Cap'n? We'd get TWO plots? No plots? What about sending
data to the autopilot? We're installing a B&G 1000h Pilot with
electric actuator to the rudder. What happens if it gets CONFLICTING
data? I'm sure it would go CRAZY trying to steer the boat to two
points at once. Sound reasonable? So we need to be able to turn off
data to the input ports, or configure the various talkers to not send
out ALL the statements they can generate.
So, this is going to take some programming thought on all the
instruments talking to the network. It's not just plug 'n pray.
We've decided, normally, the WAAS-GPS and chart plotter in the
Raymarine color radar/chart plotter with the chart plugs in it will be
the primary source of GPS information all around. As we also have B&G
Network Wind, Speed and Depth instruments in the panel, they will be
the source of these statements because the B&G 1000h Pilot will be
steering from them in "Wind Mode". It will hold a course in this mode
like a steering vane....wind priority with trimming. So, any wind
data statements will be turned off from all other instruments to
prevent comflicting outputs. The Cap'n and computer are a luxury at
the chart table. It also crashes often (WinXP) and uses the most
power of all sensors, so it will be a listener primarily and a talker
in emergency. I'll switch its data output off with a manual switch,
allowing it to continue to provide data but going nowhere until the
switch is on...such as a radar failure. Same with the Garmin GPS.
It's depth/speed sensor provides backup to the B&G instruments, also.
It will be switched off normally.
Hope this doesn't drive you crazy. The boat's owner/captain just
LOVES technology. I'm simply the 3rd mate electronic tech who's
crewing along for the ride enjoying my new Icom radio toys
(W4CSC/MM2)...(c;
The multiplexer output also feeds an Icom M59 DSC VHF, Icom M602
DSC-GMDSS VHF and Icom M802/AT-140 HF/SSB GMDSS SSB on HF to the
mainmast insulated backstay at the base of the mizzenmast.
Think we'll be on course?....hee hee.....
Now, about those motorized winches....(c;
On Thu, 07 Aug 2003 23:05:11 GMT, jeannette
wrote:
Hello all,
I have been looking at the NMEA Multiplexers. They all seem to be for
multiple talkers going into a PC.
I have 1 GPS (talker) that I want to connect to a PC (The Capn), an
NMEA Repeater in the cockpit and a Radar. In fact 1 talker, 3
listeners. I have everything connected in parallel right now and it
seems to work. Is that bad???
Jeannette Bristol 32, San Francisco
http://www.eblw.com/contepartiro/contepartiro.html
Larry
Extremely intelligent life must exist in the universe.
You can tell because they never tried to contact us.