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Old 27-09-2017, 14:09   #1
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Dilemma with NMEA 0183

I am installing my new AIS. Never had one before so I had to run new wires, about 10 hours worth! When I finally got to the point of connecting it to my MFD I realized I had a problem.

The MFD has two communication ports. Currently I have DSC radio and Auto Pilot for the two ports, both going from the MFD to the respective device. So I thought easy enough. I'll send the AIS to the radio and then the radio back to the port as a "receive". The radio does have the capability to display AIS.

Now to my question. What about the baud rate? I'm sending the radio gps nav position at a lower rate than the MFD wants to see for AIS. Will the MFD automatically sense and do what it needs to do?

Or, can I simply leave the wiring as it is and plug the AIS into the receive part of the com port that sends to the radio? But again, what about the baud rate?

Here's the gear for reference:
Digital Yacht ATI1500 AIS;
Garmin GPSMAP 741xs;
Standard Horizon GX2000.

I would have simply hooked it up and tried it but I'm still waiting for an adapter for the AIS antenna. Hopefully someone can help me with this so when the adapter comes in everything will be ready to go!

Thanks,
Larry
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Old 27-09-2017, 14:26   #2
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Re: Dilemma with NMEA 0183

The AIS data will be transmitted at 38400 baud rate. You can only have one Talker on a nmea serial line, you can have multiple listeners on it.
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Old 27-09-2017, 18:23   #3
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Re: Dilemma with NMEA 0183

I understand the talker/listener aspect, sort of. Does that mean, in this case, that I can have an output on comm port 1 to one device and an input on comm port 1 from a different device. And the baud rate will send/receive accordingly?

I was always under the impression that for each output there could only be an input from the same device. But that would preclude the "many listeners" part. Maybe I understood the concept but not the application of it!
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Old 27-09-2017, 18:27   #4
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Re: Dilemma with NMEA 0183

In general you can only have one baud rate for the single port that affects both tx and Rx. The tx (talked) can be wired to multiple devices. The Rx can receive from another device.
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Old 27-09-2017, 19:39   #5
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Re: Dilemma with NMEA 0183

Thanks Paul. I''ll hook it up the the way I originally thought. If that doesn't work I guess I'll have my AP talk to the radio. Or possibly the other way around since I don't use the AP for routes, only for either wind angle or compass heading. Or not hook up the AP to the gps at all!
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Old 27-09-2017, 21:16   #6
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Re: Dilemma with NMEA 0183

Port one. 4800baud. Output to both pilot and radio. Join wires together.

Port 2. 38,400. Ais input.

You must set the speeds in the plotter settings.

Now you need to choose between taking heading from pilot or dsc input On port 1 input.... (sounds like you have neither now?)heading more useful. Or you may need a multiplexer if you want both. . Or some ais may take 4800 input and multiplex for you.
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Old 27-09-2017, 21:24   #7
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Re: Dilemma with NMEA 0183

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Originally Posted by Sailing Drummer View Post
I understand the talker/listener aspect, sort of. Does that mean, in this case, that I can have an output on comm port 1 to one device and an input on comm port 1 from a different device. And the baud rate will send/receive !

Yes but both need to be same speed. Ie. send gps to radio and rx heading from pilot on same port. Both both would be 4800 baud.
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Old 28-09-2017, 05:37   #8
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Re: Dilemma with NMEA 0183

The AIS unit you have is a transponder, so will provide GPS and AIS to the radio at 38,400, and the radio is a listener only (yellow and white wires on the GX2000). The radio can then send that same data on to the MFD at 38,400 as a talker only (gray and brown wires from the GX2000). You have to configure the radio and the MFD to use 38,400 bps for that data on that one port. You might want to tell the MFD to ignore the AIS GPS data if it is using another GPS source.

The other port on the MFD can send and receive at 4800 bps for your other instrument and AP needs.

Chip
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Old 28-09-2017, 09:32   #9
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Re: Dilemma with NMEA 0183

Another approach is to buy a multiplexer and let that do the sorting for you. They also allow your system to grow and as they are wi-fi transmitters, any device on theh boat can play.
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Old 28-09-2017, 18:40   #10
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Re: Dilemma with NMEA 0183

Thanks everyone. I definitely learned how the application of one talker many listeners works. Before, I knew that to be true but this was the first time trying to implement it. Everything is connected and working well. The only thing I haven't tried is using the "silent mode". I am able to see other AIS signals and when I use the Marine Traffic app I can see my boat also. Tomorrow I'll see if it shows when I'm silent.
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Old 28-09-2017, 18:53   #11
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Re: Dilemma with NMEA 0183

Utimate solution for current and future upgrades, including putting the data on wifi, converting to NEMA 2000, and generally future proofing the vessel:

iKommunicate – The Gateway to Signal K

Mine does all the above, talks to the ICOM 500 AIS, the Std Radio w/ gps, broadcasts to the tablet in the cockpit, and interfaces to the TackTic Micronet system, (which serves up all manner of wind, dept, TMG, etc....even voltage on the system). Network includes a RaspberriPi running OpenCPn for navigation. I am thinking of adding an Audino hat to automate the Atomic 4 into the system.

We have an older RaspberriePi that was replaced, maybe we will program that to play movies while in port.....

Whats not to like about automation?
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Old 28-09-2017, 20:05   #12
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Re: Dilemma with NMEA 0183

All AIS receivers/transceivers are required to support standard NMEA (4800 baud) They will initially attempt to connect at High Speed NMEA (38400 baud), but will drop back if it doesn't connect at the higher speed.
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Old 28-09-2017, 20:15   #13
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Re: Dilemma with NMEA 0183

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All AIS receivers/transceivers are required to support standard NMEA (4800 baud) They will initially attempt to connect at High Speed NMEA (38400 baud), but will drop back if it doesn't connect at the higher speed.
Really? Can you point me to one of these auto-adjusting units? The ones I've played with must be manually set to the correct port speed.
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Old 28-09-2017, 20:55   #14
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Re: Dilemma with NMEA 0183

https://www.humminbird.com/WorkArea/...t.aspx?id=5947
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