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TakeFive 01-12-2011 09:49 AM

NMEA over Bluetooth
 
[NOTE: Before posting questions and responses to this thread, first read this other thread that gives more details of the completed project. Some of your questions might already have been answered.]

I am starting to buy the components (Seatalk cables, Seatalk/NMEA converter, baud rate converter) needed to get my instruments to talk to each other via NMEA. I would like to send the NMEA signal to a Netbook wirelessly via Bluetooth.

The most popular Serial-Bluetooth adapter seems to be one by IOGEAR (GBS301), but people complain that it does not support DTR/DSR handshaking. My RS232 skills are about 20 years rusty, and I'm brand new to NMEA, so I'd like to know if this will be a problem. Have any of you actually done NMEA over Bluetooth, and if so did you use the IOGEAR device?

Another device I'm considering is this, which offers the advantage of drawing its power from a USB cable:

Serial Bluetooth RS232 port adapter

Is anyone familiar with that one? Other suggestions?

sailingdog 01-12-2011 11:07 AM

Why not use an NMEA-to-BlueTooth bridge instead?

TakeFive 01-12-2011 11:21 AM

Quote:

Originally Posted by sailingdog (Post 685988)
Why not use an NMEA-to-BlueTooth bridge instead?

No reason not to, if I were willing to pay 20x more for their device instead of using commodity computer equipment.

sailingdog 01-12-2011 11:36 AM

BTW, NMEA doesn't support any hardware handshaking, so the IoGear's limitations shouldn't be an issue. :D NMEA 0183 doesn't support handshaking of any sort AFAIK.

brak 01-12-2011 12:37 PM

It should be fine. For practical purposes modern NMEA 0183 is a plain RS232 without any handshaking, any standard claims otherwise notwithstanding.

I see that its minimal baud rate is 9600. Rather than using a baud converter (which seems one moving part too many), why not pick another adapter that supports 4800 baud natively? Google brings up this: Wireless Serial Port - Wireless RS232 - Wireless Serial Cable Replacement - Bluetooth RS232 - LM058 - LM158 - BTD-433 - BTD-430

BTW, how do you power it up? I didn't find anything about power requirements in the spec.

TakeFive 01-12-2011 01:53 PM

Quote:

Originally Posted by brak (Post 686031)
...I see that its minimal baud rate is 9600. Rather than using a baud converter (which seems one moving part too many), why not pick another adapter that supports 4800 baud natively? Google brings up this: Wireless Serial Port - Wireless RS232 - Wireless Serial Cable Replacement - Bluetooth RS232 - LM058 - LM158 - BTD-433 - BTD-430

BTW, how do you power it up? I didn't find anything about power requirements in the spec.

The IOGEAR does support 4800 baud - you just have to configure it with a terminal emulator instead of using the DIP switches. That's not why I have the baud rate convertor.

Sometime when I have more time I'll convert my hand-drawn schematic to a form that I can upload and show all of you. But in a nutshell, my first priority is to install the GX2150 VHF/DSC/AIS receiver that I recently ordered (and have not yet received) and interface it with my GPS/chartplotter setup. I also have a couple of SeaTalk instruments that I would like to interface so I can consolidate depth readings with everything else, and maybe to enable track-mode on my autopilot. But the Seatalk stuff is just "nice to have" not "must have," so if the conversion equipment ends up costing too much I'm not going to do that part of the project.

The new GX2150 improves on the GX2100 by allowing you to set the DSC input to 38,400 baud, so it multiplexes the AIS and DSC onto one port if you run at 38,400. (There are other threads on this topic.) But Seatalk only runs at 4800 baud. So using the baud rate converter to interface with Seatalk allows me to use only one Bluetooth port at 38,400 instead of needing two at different baud rates. It also eliminates a multiplexer, since Seatalk has its own built-in multiplexing capabilities by combining multiple instruments (in my case, depth and autopilot) into one Seatalk chain.

That Miniplex device is real nice because it combines multiplexing, Seatalk conversion, and perhaps baud rate conversion all into one device. But dealers are listing it at $400-700, and I've already found the BT and baud converters for about $20 each.

I can't find any specs on the IOGEAR's power requirements. It comes with a 120v AC adapter, but don't know if the adapter outputs 5v or 12v, don't know the amp draw, and don't know whether the connector is proprietary. The USConverters one runs off of a USB cable, which means it's 5 volts and less than 500 mA IIRC, and obviously there are 12v USB converters everywhere. So I'm leaning toward the latter because of the same power issues that you mentioned.

brak 01-12-2011 02:29 PM

That sounds pretty darn interesting :)

One point I am missing - so you have a 38K output from DSC/AIS and 4.8K output from Seatalk/NMEA. How do you put both those outputs onto a single bluetooth converter?

As an aside, what I'd really like to see is NMEA2000 to bluetooth converter. Literally raw data encapsulation - CAN bus packets minimally wrapped (length, magic number), sent over bluetooth for computer to read and process as needed. I am sure NMEA would never certify this - but who cares, that'd be a great way to interface software with NMEA2000 stuff. But I digress.

TakeFive 01-12-2011 02:48 PM

Quote:

Originally Posted by brak (Post 686065)
That sounds pretty darn interesting :)

One point I am missing - so you have a 38K output from DSC/AIS and 4.8K output from Seatalk/NMEA. How do you put both those outputs onto a single bluetooth converter?

This gets to the part I'm not as sure about - I'll need to try it out. It depends on whether Seatalk echos or passes through NMEA sentences that it receives [EDIT: Seatalk Technical Reference says it does pass through NMEA sentences]. If so, it should work. My first try would be to feed the GPS sentences that come from the Bluetooth converter into Seatalk (using baud converter and Seatalk converter in series). Hopefully the Autopilot uses the GPS sentences that it gets from Seatalk, depth sounder adds its info onto the Seatalk chain, and the Seatalk converter then spits it all back out into the GX2150 input. The GX2150 uses the GPS coordinates for its DSC and for prioritizing the AIS readings, and spits out the DSC, AIS, and depth info to the Bluetooth converter, and it all makes its way to the chart plotter. [EDIT: Unfortunately this will not work as I described here. NMEA devices will receive sentences in and transmit their own sentences out, but they do not generally pass through the sentences that they receive. So I would need a multiplexer to do this.]

This is all a lot easier to follow in a schematic.

It's been a long time since I did serial interfacing, so I'll have to try it and see if it works. That's part of the reason I want to do it on the cheap, so I don't get stuck with a lot of expensive gear if I don't like it.

The other thing that I know will stir up a lot of controversy here is I plan to buy a RAM mount to put my Netbook in the cockpit. I'm a fair-weather daysailor, and did not get a drop of water in the cockpit last year. My Netbook is sitting virtually unused and has a matte finish screen that is incredibly bright - can see it easily in full daylight. And OpenCPN does a really nice display of AIS data. So I'll keep using my Garmin handheld as my primary device, but will have a bigger, brighter screen with AIS data on the Netbook. If it rains or starts splashing, I'll move the Netbook down to the cabin (Bluetooth will be nice for that) and just use the handheld in the cockpit like I did all last year.

brak 01-12-2011 03:27 PM

Quote:

Originally Posted by RhythmDoctor (Post 686068)
This gets to the part I'm not as sure about - I'll need to try it out. It depends on whether Seatalk echos or passes through NMEA sentences that it receives.

not as a general rule, and very unlikely to pass AIS.

Quote:

The other thing that I know will stir up a lot of controversy here is I plan to buy a RAM mount to put my Netbook in the cockpit.
not from me :) nothing wrong with using a laptop as long as you take reasonable care and understand any potential limitations. though for obvious reasons my opinion on software selection would differ.


I got my netbook splashed a few times, thanks to wakes of passing powerboats. It's still doing ok.

TakeFive 01-12-2011 06:22 PM

OK, here are two possibilities of what I might do. Note that a one-directional arrow represents a pair of wires for a half-duplex NMEA connection. Bi-directional arrows are Seatalk cables.

"Plan A" is what I attempted to describe above. If it works, it would interface depth, DSC, and AIS all to the chart plotter through Bluetooth, and also send GPS coordinates to the ST4000+ autopilot and radio. Note that there are two ways to send GPS to the autopilot connection: 1) wire it into Seatalk through the B&B baud converter and E85001 Seatalk converters into the ST30 depth gauge or 2) take it through the baud rate converter to the autopilot's NMEA input terminals. I denoted these two sub-options with dashed arrows.

I don't see a problem here with AIS getting to the Bluetooth adapter, because it is connected directly without going through Seatalk. The potential problem I see is that Seatalk may not pass through the GPS coordinates to the radio:


So if Plan A does not work, or I can't find the E85001 Seatalk converter for a price that I am willing to pay, this simplified "Plan B" arrangement should definitely work. It will not allow for displaying depth on my chart plotter, but the Seatalk cable between the depth and autopilot will allow display of depth on my Autopilot display panel. This is important because my view of the depth panel is frequently blocked by passengers in the cockpit, but the autopilot panel is much more conveniently located. It's a cleaner option that cutting a new hole and patching the old one to relocate the ST30 panel:



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