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

One talker with 3 listeners should be O.K. if the GPS has enough output
to drive all three. Multiplexers are only required when there are
multiple talkers. The multiplexed will combine the output sentences and
the listening devices will only respond to sentences they understand.

Kelton
s/v Isle Escape

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

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.

I'm running into similar problems and questions with the talker conflict..

I have my GPS sending the NMEA sentence to the my laptop serial port. The
Capn recieves that position data etc for my plot.

I then can have The Capn send Cross Track info to my Auto Pilot interface
for course correction.

However, The Capn appearently sends the AP XTE data out the same port as the
GPS input.

Is The Capn doing any multiplexing or timing of this data??

When I monitor the NMEA data sentences from the GPS, using Hyper Terminal, I
see that the GPS is out puting a XTE, APA & APB sentences.

(I haven't yet, figured out how to turn off the GPS XTE output. There always
seems to be some data in these sentences.)

Or! (thinking out loud) Is it possible to just connect the laptop serial
Data out and Data Com to the AP interface while leaving the serial Data in
and Data Com connected to the GPS. This would create a second NMEA data
stream, wouldn't it?? (I think that is the way I have it right now, and it's
not working)

I really wish I could find a way to make The Capn output the AP XTE to a
seperate serial port. Sure would make life easier.

Steve
s/v Good Intentions

"Steve" wrote in message
...

Or! (thinking out loud) Is it possible to just connect the laptop serial
Data out and Data Com to the AP interface while leaving the serial Data in
and Data Com connected to the GPS. This would create a second NMEA data
stream, wouldn't it?? (I think that is the way I have it right now, and
it's
not working)

Should be working, since it would be the same situation as having The Cap'
sending out over a different serial port.

Meindert

Yah! It should be and I suspect I may have a wiring error from the serial
Data Out or Data Com. going to the interface.

The interface just sits in 'idle' mode with the red and green led flashing,
waiting for a XTE.

I may just try hooking the interface directly to the GPS and see if it will
recognize the XTE from the there..

I don't want to steer or control the AP from the GPS since it is too
difficult to program in the WPs and Routes. (being an older gps that I can't
upload these from the laptop.)

Thanks for the reassurance.. means I should check my wiring, etc.

Steve
s/v Good Intentions

Since I posted last, I called the engineering company down in Florida
because the multiplexer had no output on its TLK terminals with all 4
ports full of active data. TX had data out to the computer great,
though.

This unit was designed with The Cap'n in mind, i.e. to have the
computer online all the time. The company explained to me that if I
wanted to use the multiplexer without the computer, I'd have to
connect my NMEA listeners to the computer port TX line, not the NMEA
output which is but a level converter/repeater for the RX port coming
back from the computer. He also warned me there was only 15ma of
current available, but all my listeners are very high impedance so
that's not an issue, so far.

So, I added yet another DPDT mini toggle switch to switch the Master
Network Output between the TX terminal and the TLK terminal, depending
on whether you want to use the computer's output, or save power and
use the multiplexer's output direct without computer intervention.
Works great. You can even have the computer online "watching" and
computing as a listen, with the system ignoring its processed output
because it isn't hooked to anything.

GPS SOURCE now has two switches....Computer? (Y/N).....and.....Garmin
GPS or Raymarine display (radar, gyrocompass, WAAS-GPS).

I thought I was going to have a conflict over depth because the Garmin
has depth output from its own sonar plotter, but so does the B&G Depth
instrument on the panel. The system seems to like the Garmin better
when the switch is in the Garmin position, displaying that on the
Raymarine, for instance, then using the B&G Depth output when the
Garmin is not switched in and it's the only thing available.

I've also gotten a chartplotter point from a DSC emergency on Channel
70 on the Raymarine chart plotter display. The bridge was blocking
the radar in his direction so I didn't see an echo from him but his
lat/long was indicated properly. Radio is the Icom M602 DSC VHF from
the mainmast 3db Shakespeare at 55 ft up.



On Sat, 13 Sep 2003 14:12:19 -0700, "Steve" wrote:

Yah! It should be and I suspect I may have a wiring error from the serial
Data Out or Data Com. going to the interface.

The interface just sits in 'idle' mode with the red and green led flashing,
waiting for a XTE.

I may just try hooking the interface directly to the GPS and see if it will
recognize the XTE from the there..

I don't want to steer or control the AP from the GPS since it is too
difficult to program in the WPs and Routes. (being an older gps that I can't
upload these from the laptop.)

Thanks for the reassurance.. means I should check my wiring, etc.

Steve
s/v Good Intentions




Larry W4CSC

3600 planes with transponders are burning 8-10 million
gallons of kerosene per hour over the USA. R-12 car air
conditioners are responsible for the ozone hole, right?

On Sat, 13 Sep 2003 14:12:19 -0700, "Steve" wrote:


I don't want to steer or control the AP from the GPS since it is too
difficult to program in the WPs and Routes. (being an older gps that I can't
upload these from the laptop.)

You may not want to steer directly from the hard-to-set-up GPS
waypoint NOW, sitting here smiling at the dock.....but I disagree in
not setting the system up to provide it with a direct switching
arrangement bypassing all the fluff when you need that damned AP
hooked to the surviving old GPS in a full gale to steer the course
while you're trying to shorten sails before they blow out.

The switch path on Lionheart looks like:

gps source sw
GARMIN 185-- | ------RAYMARINE RL70CRC PLUS
|
| emerg/normal sw
MPX in 1----------|---------- |--------Network Out
|
DSC RADIOS
AUTOPILOT
all other NMEA listeners


Network Out comes from the switch between multiplexer (MPX) outputs TX
(no computer) and TLK (from The Cap'n). Selecting EMERG on the bottom
switch and either surviving GPS source on the top switch continues to
steer the autopilot and update the DSC position data DIRECTLY from ONE
GPS talker, bypassing the multiplexer and other instruments in an
emergency situation. I like lots of backup paths that do NOT require
"wiring in the storm".




Thanks for the reassurance.. means I should check my wiring, etc.

Steve
s/v Good Intentions




Larry W4CSC

3600 planes with transponders are burning 8-10 million
gallons of kerosene per hour over the USA. R-12 car air
conditioners are responsible for the ozone hole, right?