** Bi-directional link **

Discussion and support for the Nmea4Wifi multiplexer - a 4-input Nmea 0183 wifi multiplexer.
Post Reply
User avatar
Posts: 22
Joined: Wed Apr 03, 2019 8:19 am

** Bi-directional link **

Post by schnapsy » Sun Nov 21, 2021 11:22 am

Hello Luis,

My question may be stupid, but I'm going ...

On my next boat, I will be able to receive with the Nmea4Wifi all the information (sensors, GPS, AIS) on the tablet of my PC 2 in 1, Thougbook CF-33.
This tablet is waterproof, 1300 nits, 2 batteries and I don't want to connect a cable to it.
My problem is with the autopilot, if I want to send it the nmea data of the route followed, from the tablet.

OpenCPN allows to receive and transmit data Nmea0183.

Hence my question: is it possible to send and receive data via the Nmea4Wifi ?

More precisely :
- on the tablet in the cockpit OpenCPN receives data from the sensors in TCP;
- on the same address (?), it returns only road data (XTE, RMB, etc.)
- these road data are received on the Nmea4Wifi which "retransmits" them in wired format to the autopilot.

My boat is currently over 500 km (abroad) and with the restrictions related to Covid, travel is currently difficult and I cannot do the tests directly ...
So if this manipulation is possible, it allows me - in the meantime - to take care of something else.

Thanks in advance,

Posts: 207
Joined: Wed Mar 04, 2020 6:36 pm

Re: ** Bi-directional link **

Post by dagnall » Sun Nov 21, 2021 6:17 pm

I can answer this for Luis, as I have almost exactly the same configuration on my Boat. I even had a setup some time ago that used a Tough Book!

First. When you use TCP, the link IS bidirectional (on the same Port number), and if your application can send routing data, then by setting "TCP>P5" in the multiplexer, this TCP data from OpenCPN will be routed to come out of P5. (I connected P5 directly to my Raymarine Autohelm, and then RMB,XTE etc data from OpenCPN will be sent to the autopilot.)

Although you will probably have P1>TCP and P2>TCP (etc), to get data from the boat instruments to the Tough Book, this data is NOT retransmitted out of P5 to the Pilot UNLESS you ALSO select P1>P5 (or P2>TCP etc.)

It is important to note that the multiplexer can only connect "TCP" to a single Computer/Phone/Tablet etc, and that a TCP Port will need to be specified, as the default NMEA4 sets this to "0". I used port 3000.

Although the Toughbook was nice, I actually now use iNavX on my Iphone and Ipad. For your interest, this is my setup. You will see that P2 (AIS) is sent to TCP and UDP but NOT to P5, so no !AIS messages are sent to the Pilot.
GPS (P1) IS copied to the pilot, so I can get COG and SOG from GPS to show on the Pilot.
The laptop can see all data received on Seatalk, P1,P2 and P4. And anything sent from the laptop is sent out of P5 (to the pilot).

Note that I have Seatalk1 wind instruments so they are direct connected to the pilot. This allows me to "sail to wind".
If you wanted to use a NMEA0183 Wind instrument (say on e.g. P3) then to send wind data to the Pilot you will have to direct this data to P5 as P3>P5 (etc).

I hope that covers everything?

Best Regards,
Boat Electronics.jpg

User avatar
Posts: 22
Joined: Wed Apr 03, 2019 8:19 am

Re: ** Bi-directional link **

Post by schnapsy » Sun Nov 21, 2021 6:57 pm

Hello Dagnall,

A big thank you for this precise and very detailed answer, which answers exactly what I "wanted" to hear.

This corresponds and confirms what I had read in the user manual provided by Luis.
I will have more or less the same setup as what you described, and your diagram is very informative.

As soon as I can go on the boat, I will try to implement what you have described and which fully satisfies me.

Best regards,

Post Reply