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Old 06-12-2010, 16:43   #1
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Question Nema Multiplexer Needed or Not ?

I currently have a Gps connected to my Nexus FDX which is connected to a laptop supporting Nobeltec nav software.

Over the winter I'm adding a Ray wheel pilot and a Sitex radar chart plotter.

Can I just wire the needed nema in/outs together on a small buss block or do I need a multiplexer to resolve all this nema exchange?

Here's a bit more info

furuno gps-32, nema in/out now used with Nexus

Nexus FDX nema out wind speed, true & apparent,compass mag heading used with Nobeltec

laptop with Nobeltec
--------

Sitex Radar chart plotter Color Max Sealink I, internal gps, also possible to add external gps with two nema ports

---------

Auto Pilot Raymarine wheel X-5, supports the following NMEA0183 sentences.

NMEA0183 to Course Computer
NMEA0183 from Course Computer

* The computer will only transmit these items if it has received the appropriate data.
Header Data in
APB Cross track error, bearing to waypoint, waypoint number
BWC
BWR
Bearing to waypoint, distance to waypoint, waypoint number, time
GGA
GLL
Latitude/longitude, time
HDG
HDM
HDT
Heading
MWV Apparent wind angle, apparent wind speed
RMA Course over ground (COG), speed over ground (SOG), latitude/longitude,
variation
RMB Cross track error, bearing to waypoint, distance to waypoint, waypoint
number
RMC Course over ground (COG), speed over ground (SOG), latitude/longitude,
time, variation
VHW Speed through water, heading
VTG Course over ground (COG), speed over ground (SOG)
XTE Cross track error
ZDA Time, date

Header Data out
HDG Heading
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Old 06-12-2010, 17:44   #2
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You should use a multiplexer. While several inputs might be successfully paralleled, outputs should not be paralleled for several reasons.
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Old 07-12-2010, 18:12   #3
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I went searching around for multiplexers,

Noland appears to be clueless.

"I am not sure what a Nexus "FDX" is.

Contacted Brookhouse, super helpful, will follow up with them.
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Old 07-12-2010, 21:35   #4
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Brookhouse is good. You might also look at ShipModul : ShipModul Marine Electronics. I've used a few Shipmodul muxes, and I like them.
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Old 07-12-2010, 23:33   #5
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Without understanding the details of your installation, it may be possible to avoid a multiplexor and instead utilize a serial/USB combiner - something at Digi Products sells (not cheap, this is commercial networking equipment).

Essentially, if you have multiple serial outputs (which NMEA is) then you could run them into a combiner such that you can have multiple NMEA talkers driving to a single listener. I'm using the Digi Edgeport 8 to bring in NMEA data and forward it along to the laptop, so far it has worked flawlessly for two years on the boat.

- rob/beetle
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Old 07-12-2010, 23:36   #6
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Quote:
Originally Posted by Jimbo2010 View Post
Can I just wire the needed nema in/outs together on a small buss block or do I need a multiplexer to resolve all this nema exchange?
You will need some sort of hardware solution (other than a bus block) that will combine the talker NMEA sentences into a single-threaded sentence that can be forwarded to an NMEA listener. If you don't do this, then the data being passed around can become corrupted.

So no, don't just wire together the various NMEA talkers to a common pair of wires - you are unlikely to be pleased with the results.

- rob/beetle
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Old 08-12-2010, 02:54   #7
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I must be misunderstanding something because I donít see why a multiplexer is essential.
I assume the system is working OK as it is.

Also connect the GPS NMEA out (in parallel) to the autopilot and chartplotter.
If you want the facility for the autopilot to go to the waypoint a simple switch will divert the autopilot NMEA from the GPS to the chartplotter.

The NMEA will be driving 4 things, but it should cope fine with this.
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Old 08-12-2010, 03:13   #8
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Quote:
Originally Posted by daddle View Post
You should use a multiplexer. While several inputs might be successfully paralleled, outputs should not be paralleled for several reasons.
Better to say that NMEA 0183 "talkers", GPS, wind & depth senders for example, cannot be connected/paralleled up. There are two main reasons it doesn't work:
1) There is no data synchronisation in NMEA 0183, so you will have individual data sentence crashes.
2) Although less likely, an impedance mis-match on the senders could completely wipe out the signal from another.

To feed multiple talker devices to a single listener (e.g. chartplotter) you will need a multiplexer.

You can however connect several listeners to one talker. A classic example is feeding the NMEA 0183 output of your GPS to a common bus then connecting your DSC VHF, chartplotter & PC etc. to this common bus.

The limitation on just how many individual listeners can be connected depends on impedance of each & so how they will load the source, but with modern equipment five or more is possible.

Another option as mentioned above is to use the multiple COM port inputs available on many PC based chartplotters. In such case you could use multiple COM port adapters (or single multi-port one) to feed your data sources separately. In this case the chartplotter software does the multiplexing.
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Old 08-12-2010, 05:30   #9
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Quote:
Originally Posted by beetle View Post
Without understanding the details of your installation, it may be possible to avoid a multiplexor and instead utilize a serial/USB combiner - something at Digi Products sells (not cheap, this is commercial networking equipment).

Essentially, if you have multiple serial outputs (which NMEA is) then you could run them into a combiner such that you can have multiple NMEA talkers driving to a single listener. I'm using the Digi Edgeport 8 to bring in NMEA data and forward it along to the laptop, so far it has worked flawlessly for two years on the boat.

- rob/beetle
Problem there is I believe I have too many connections.

Moreover, that cost more ($325) than proven multiplexers
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Old 08-12-2010, 05:35   #10
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Originally Posted by richardhula View Post
Better to say that NMEA 0183 "talkers", GPS, wind & depth senders for example, cannot be connected/paralleled up. There are two main reasons it doesn't work:
1) There is no data synchronisation in NMEA 0183, so you will have individual data sentence crashes.
2) Although less likely, an impedance mis-match on the senders could completely wipe out the signal from another.

To feed multiple talker devices to a single listener (e.g. chartplotter) you will need a multiplexer.

You can however connect several listeners to one talker. A classic example is feeding the NMEA 0183 output of your GPS to a common bus then connecting your DSC VHF, chartplotter & PC etc. to this common bus.

The limitation on just how many individual listeners can be connected depends on impedance of each & so how they will load the source, but with modern equipment five or more is possible.
I agree based on what I've learned to date.

Quote:
Another option as mentioned above is to use the multiple COM port inputs available on many PC based chartplotters. In such case you could use multiple COM port adapters (or single multi-port one) to feed your data sources separately. In this case the chartplotter software does the multiplexing.
Problem with using the laptop as the heart of the system is that would not have any redundancy designed in the layout.

Looking at the book on the Sitex chartplotter I don't see that it could handle it.
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Old 08-12-2010, 05:40   #11
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Reply from Brookhouse;

NMEA inputs can be combined (connected in parallel) to share a single input, for multiple NMEA outputs a multiplexer is required to combine the data for a single NMEA input port.

If you want to combine Furuno GPS, Nexus instrument data and auto pilot output (heading from fluxgate compass)to be input by chart plotters and computer via single ports, you will need a multiplexer. A standard model will do the job, but if you consider ever adding AIS in future, our multiplexer model AIS would be a better choice.

To control the AP in "track mode" to steer to a waypoint or along a route, from either chart plotter or computer,a switch would need to be installed.


Do not send all possible NMEA sentences to the AP, there is much duplication of data. Send APB, RMB, RMC and VTG. MWV if you want to steer in vane mode.

I replied.......

"To control the AP in "track mode" to steer to a waypoint or along a route, from either chart plotter or computer, a switch would need to be installed. "



Can you explain please how the switch is done?


In looking at this install redundancy is near the top of the list, currently if the laptop or furuno went out Iím back to paper charts.

The Sitex Radar chartplotter can be the backup system. Also this unit has an internal GPS.
I see that the multiplexer can read one as a primary and the other as a secondary.
Thatís a super feature!!! But that would take up two ports wouldnít it?

I think the Ais model is a better choice, yes.

The AP although from Raytheon Iím going to use the nema rather than Seatalk unless you disagree?

The AP comes with a Fluxgate, I also have one with the Nexus data.
How should I use those two units? Another user tells me ďif you have both an external NMEA compass ie; Nexus input with the X-5 Raymarine compass input, it will default to using the Raymarine compass.Ē

He also added ďThe Track mode driven by the GPS works ok, but you need to be near zero XTE when you start it. The X-5 tries to maintain zero cross track error, and if you are to left or right of track when entering that mode, the X-5 steers a sharp angle to get the XTE to zero, then will follow the course. It doesn't head directly to the waypoint. Once on the track with zero XTE, the position keeping is good heading to the waypointĒ

With that in mind should I send XTE or will RMB suffice?

NX2 server has 16 slots taking 2sec to transmit.

So I can program the data exported from the within the Nexus and add Furuno output into one port.

That output now needs to go to the laptop, AP, chartplotter

Iím a bit lost at this point, what comes and goes to the other ports on the Multiplexer with AIS?




I'll let you know their reply,




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Old 08-12-2010, 06:33   #12
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Quote:
Originally Posted by beetle View Post
Without understanding the details of your installation, it may be possible to avoid a multiplexor and instead utilize a serial/USB combiner - something at Digi Products sells (not cheap, this is commercial networking equipment).

Essentially, if you have multiple serial outputs (which NMEA is) then you could run them into a combiner such that you can have multiple NMEA talkers driving to a single listener. I'm using the Digi Edgeport 8 to bring in NMEA data and forward it along to the laptop, so far it has worked flawlessly for two years on the boat.

- rob/beetle
which pins on the serial connector get the + - wire from the NMEA talkers
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Old 08-12-2010, 08:19   #13
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which pins on the serial connector get the + - wire from the NMEA talkers
NMEA (+) to DB-9 pin 2, NMEA (-) to DB-9 pin 5. That's what my notes have regarding making up my own connectors using $5 in parts from Fry's Electronics ; I also found it helpful to pick up the little pin insert/extract tool to manipulate the pins.

- rob/beetle
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Old 08-12-2010, 10:55   #14
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With that in mind should I send XTE or will RMB suffice?
RMB contains all of the XTE data, so either one might do the job. You need to look at what your autopilot is expecting to receive.
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Old 08-12-2010, 14:35   #15
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Ok just heard back from Brookhouse, these guys are great so far as to support.

----

"To control the AP in "track mode" to steer to a waypoint or along a route, from either chart plotter or computer, a switch would need to be installed. "



Can you explain please how the switch is done?

For switching between computer and plotter:
Assuming multiplexer model AIS, 38400 baud output from computer (USB) and chart plotter (NMEA out):

DPDT (double pole double throw) (mini) switch. Common: Mux RS232 Rx / Gnd, pos 1: blue wire mux and RS232 Gnd, pos 2: plotter NMEA out.

In looking at this install redundancy is near the top of the list, currently if the laptop or furuno went out Iím back to paper charts.

The Sitex Radar chartplotter can be the backup system. Also this unit has an internal GPS.
I see that the multiplexer can read one as a primary and the other as a secondary.
Thatís a super feature!!! But that would take up two ports wouldnít it?


To switch between 2 GPS units you need 2 4800 input ports of the mux or manual DPDT switch

I think the Ais model is a better choice, yes.

The AP although from Raytheon Iím going to use the nema rather than Seatalk unless you disagree?

To control the AP from non-Ray plotter or computer you'll have to use NMEA input.
The AP comes with a Fluxgate, I also have one with the Nexus data.
How should I use those two units? Another user tells me ďif you have both an external NMEA compass ie; Nexus input with the X-5 Raymarine compass input, it will default to using the Raymarine compass.Ē

The AP uses its internal fluxgate
He also added ďThe Track mode driven by the GPS works ok, but you need to be near zero XTE when you start it. The X-5 tries to maintain zero cross track error, and if you are to left or right of track when entering that mode, the X-5 steers a sharp angle to get the XTE to zero, then will follow the course. It doesn't head directly to the waypoint. Once on the track with zero XTE, the position keeping is good heading to the waypointĒ

Correct
With that in mind should I send XTE or will RMB suffice?

No, APB, VTG, RMB/RMC APB contains most steering parameters, incl XTE
NX2 server has 16 slots taking 2sec to transmit.

So I can program the data exported from the within the Nexus and add Furuno output into one port.

Nexus NMEA OUT and Furuno NMEA OUT on separate mux input ports at 4800 baud.
That output now needs to go to the laptop, AP, chartplotter

No, not directly to AP, to laptop and chart plotter. Laptop or chart plotter generate AP commands when an waypoint is made active.
Laptop or chart plotter output to mux @ 38400 baud via switch. Mux converts 38400 to 4800 for compatibility with AP. See baudrate conv option 1 here:
Baudrate conversion

38400 is mux output baudrate because model is AIS. Check if plotter supports this..
Iím a bit lost at this point, what comes and goes to the other ports on the Multiplexer with AIS?

See above plus port 4 receives data from AIS receiver.




What do u guys think?




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