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Go Back   SailNet Community > On Board > Gear & Maintenance > Electronics
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  #1  
Old 01-25-2011
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Sending GX2150 AIS NMEA data to chart plotter over Bluetooth

I thought I would put in an update on my instrumentation plan from what I had posted on another thread. I have a much smaller and simpler boat than many of you, but nevertheless maybe someone else can benefit from seeing what I'm doing, and/or offer advice on what I can do better. As you can see, I have relatively little instrumentation, but I am interested in doing as much with what I have as possible without taking out a second mortgage to finance it. Most of this is driven by the new GX2150 VHF/AIS radio that I have on order, and since many others may be adopting AIS in the future, this might help someone.

I tested most of the components shown on the other thread over the past week. The Seatalk-NMEA bridge from Raymarine worked fine, but it has a defect that will require it to be returned (glad I got it from WM, and not from an ebay seller). Since its only purpose was to get Depth data into NMEA for display on the Netbook, I've decided it's not worth the cost or hassle. Part of this is because I learned from the Standard Horizon tech support guy that the GX2150 will not pass through the depth sentences over NMEA as I had previously hoped - it will just ignore them. So the only way to get depth and AIS into NMEA is to add a multiplexer. And a mux/SeaTalk translator is more than I was willing to pay at this time. Maybe I'll do that next year if I add an electronic wind gauge.

Also, my prior design was too dependent on having the Netbook turned on all the time to pass the GPS data to the radio. DSC and AIS are important enough that they deserve a dedicated GPS, so I've ordered a Garmin 18x LVC. I plan to configure this so that the other GPS in the cockpit can be tethered to the Netbook and passed by Bluetooth to the AutoPilot if I want to run in track mode. The Netbook would have to be on for that, but I will do this only rarely. I've left the Baud converter in the design because it allows me to run the AIS input at 38400 baud. According to the GX2150 manual, doing this causes both the AIS and DSC targets to multiplex onto a single port at 38400 baud. Alternatively, I could eliminate the baud converter by running the 18x GPS data into the radio at 4800 baud, but then the AIS and DSC targets would come out from the GX2150 via two separate ports at two different baud rates according to the GX2150 manual. (Note that the GX2100 is limited to operating in this mode, which is why I am waiting for the GX2150.)

So here is my schematic - comments welcome:

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Formerly posted as "RhythmDoctor"
1998 Catalina 250WK Take Five (at Anchorage Marina, Essington, on the Delaware River)
1991 15' Trophy (Lake Wallenpaupack)
1985 14' Phantom (Lake Wallenpaupack)

Last edited by TakeFive; 01-25-2011 at 08:50 PM.
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Old 02-01-2011
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baud converter

You may have a problem if more data arrives at the high-speed side of the converter than can be delivered at 4800 - like overfilling the big end of the funnel, some of it doesn't go out the narrow end. Unless the converter is smart enough to recognize and drop full NMEA sentences, it will likely just drop data whenever it overflows which may chop up the sentences you want.

I use a Raymarine E85001 to feed NMEA to a serial terminal server on my internet feed (to check on wind speed/dir/temp when the boat is in winter storage, as it is now), and occasionaly plug in a serial-bluetooth adapter to drive laptops. I do have an Actisense mux which combines radio DSC (no AIS yet, but soon) with the autopilot "fast heading" output to drive my E80/E120. The mux and E85001 are not connected however; they are basically separate NMEA networks.

Originally I tried the NMEA output of an ST60 Graphic to drive my internet feed and laptop, but for some reason none of them (I have three) would provide all the sentences the manual said they would. The E85001 does a better job. As they seem a bit fragile, I did buy a spare (both on eBay).

In the "gadget" category, here at home I currently have the spare E85001, a spare ST60 Wind (rendered spare when one failed and I replaced it while having the first one repaired) and an ST60Multi (which was replaced with a Graphic aboard) plugged into a serial/ethernet box configured to autoconnect to the one on the boat. So by turning on power, I have a Wind and Multi on my desk echoing what's being displayed aboard, within a few seconds of real time. Somehow make the boat and spring launch date seem not quite so far away.
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Old 02-02-2011
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Thanks for the advice. I share your concern about overloading the buffer on the baud converter, but since I am only sending GPS sentences once a second (not a whole bunch of multiplexed stuff) and these sentences are typically sent at 4800 baud via "standard NMEA", I am hopeful that I will have no overflow issues. The reason I'm sending it at 38400 is not because of increased bandwidth - it's because the system is simplified if I send it at the same baud rate that I receive the AIS data (only need one Bluetooth dongle and the radio multiplexes DSC and AIS onto the same port).

I agree that the E85001 is fragile. The "defect" that I referred to above was a smell of burning phenolics after I had it in use for about 5 min. I pulled it apart and saw a black spot on the bottom of the PC card (although it continued to work OK). After multiple calls to various tech support people I was assured that it was a component failure, not something that I caused. But it scared me enough that I decided to design it out of my system. Right now the only benefit it was giving me was putting depth into the chart plotter program, and I'd need to add a multiplexer to make that work anyway, which is just more cost than I want to bear right now.

FYI, the 18xLVC and Bluetooth converter came in yesterday. Although the radio is not in yet, I was able to connect the 18x to the Bluetooth converter, and get GPS fixes into OpenCPN wirelessly. I had previously tested the baud converter, so it looks like all the components are going to work. I just need to wait for the radio before I can hook them up the way I want them.
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1991 15' Trophy (Lake Wallenpaupack)
1985 14' Phantom (Lake Wallenpaupack)
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Old 02-05-2011
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The problem with this is that the AIS data will also be passed to the baud rate converter, thus causing the overflow if you are in a high AIS use area, which the Delaware is.

Also on the GX2100 - GPS data is not repeated on the AIS data line - I don't know if this is rectified on the GX2150. I have a GX2100 with a GPF300i - they play very well together, but it is a pain to have to run two serial lines to the computer to get both AIS and GPS data.

Last edited by Waterman480; 02-05-2011 at 07:17 AM.
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Old 02-05-2011
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Quote:
Originally Posted by Waterman480 View Post
The problem with this is that the AIS data will also be passed to the baud rate converter, thus causing the overflow if you are in a high AIS use area, which the Delaware is.

Also on the GX2100 - GPS data is not repeated on the AIS data line - I don't know if this is rectified on the GX2150. I have a GX2100 with a GPF300i - they play very well together, but it is a pain to have to run two serial lines to the computer to get both AIS and GPS data.
Please have another look at my "Plan E" schematic. AIS data goes directly from the radio to the Bluetooth dongle at 38400. It does not go through the baud rate converter.

SH tech support confirmed that GPS data is not repeated, in compliance with the NMEA 0183 standard. That is why the Oregon GPS is tethered to the Netbook. I am considering a further revision that will add a second Bluetooth dongle to pass the 18x GPS data to the Netbook wirelessly instead. It might be a good idea to be able to monitor the GPS fix that the DSC/AIS is getting. I'd hate to hit the "distress" button and have the wrong coordinates go out.
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Old 02-05-2011
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Drawing E shows GPS/XTE data going from the BT adapter to the baudrate converter - however the line from the GX2150 to the BT adapter contains only AIS/DSC data not GPS/XTE data - so you are missing something there.

Looking at my GX2100, I don't see the required sentences being output for the autopilot either. Reviews of the 2150 did not mention that this was added. Are you sure they are there?

Last edited by Waterman480; 02-05-2011 at 06:38 PM.
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Old 02-05-2011
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Quote:
Originally Posted by Waterman480 View Post
Drawing E shows GPS/XTE data going from the BT adapter to the baudrate converter - however the line from the GX2150 to the BT adapter contains only AIS/DSC data not GPS/XTE data - so you are missing something there...
No, the autopilot needs waypoint, XTE, SOG, etc. to run in track mode. That needs so come from a chartplotter/GPS combination. In my schematic, these sentences are transmitted by OpenCPN from the Netbook through Bluetooth to the autopilot. AIS has nothing to do with this. The AIS sentences go the other way through Bluetooth so that OpenCPN can plot the traffic.
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1985 14' Phantom (Lake Wallenpaupack)
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Ahh, that makes sense now. It was not obvious at all in the drawing. My only suggestion would be to get a good nav program like Coastal Explorer 2011, rather than OpenCapn. I have been less than impressed with the stability of OpenCpn. Crashing seems to be its middle name. (Latest version tried - v 2.3.1)
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Old 02-05-2011
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I have criticized previous versions of OpenCPN, but 2.3.1 has been completely stable in my testing so far. I also discovered a problem with my directory structure that caused some of the problems before, and after fixing it charts load much more quickly. I am going to give it a chance before forking over $400 for a commercial program.
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Old 02-17-2011
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I have revised my schematic for the wireless AIS/chartplotter once again. I decided it would be a good safety feature to be able to monitor the coordinates that the GPS dongle was sending to the radio to make sure there's a reliable fix. So I added a second Bluetooth converter to feed the GPS readings wirelessly back to the chartplotter. (The prior design had the chartplotter receiving GPS by tethering to my Garmin Oregon 400c.) Now I have full redundancy - the Oregon and the GPS/AIS/DSC/Autopilot/Bluetooth/Netbook chartplotter system are each separate standalone systems. Thanks to the wireless connection, the netbook chartplotter can be located anywhere on the boat - in the cockpit (I have a RAM Mount to put in on my pedestal guard) or down in the cabin if weather is poor. Either way, all the information goes to/from it wirelessly via Bluetooth. If I turn the netbook off (or its battery runs dead), the radio still gets GPS signals directly from the GPS dongle.

I picked up a small surface-mount network box to serve as the central connecting point for everything. I am going to use RJ45 connectors to terminate all the wires, and daisy-chain RJ45 receptacles inside the box. I'll also mount a couple of DB9 receptacles in the box, so the Bluetooth dongles will plug into the box directly. The whole thing runs off a 5v supply from a USB power adapter, and draws under 270 mA @ 5v. I've mapped out which pins on the RJ45 bus will correspond to each wire. Here's the schematic and wiring plan:

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1985 14' Phantom (Lake Wallenpaupack)
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