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Old 10-11-2012, 04:28   #1
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NMEA via ethernet/wifi

Hi,

We're just getting into electronic navigation gadgets - strange really, since I work with computers, but for navigation we've never had anything more advanced more than a handheld GPS before (and that was met with some resistance...).

We've just bought a new DSC VHF with builtin AIS receiver (Standard Horizon GX2100E), and of course we'll be connecting this to the GPS (a Garmin handheld) by NMEA to get position data into the VHF/AIS.

While we're about it, it seems logical to make the NMEA data available to the computer - both so we can use OpenCPN for navigation, should we ever want to, and so that we can get a fuller AIS display than what the VHF affords.
The obvious way of doing this, of course, is via a serial-USB adaptor.

Now, onto my question. It seems to me that it should be possible to broadcast the NMEA data via ethernet to a router, and then via wifi, so that we can also receive the same data away from the chart table on my MacBook Pro and - what's more - on my new Android tablet (Samsung/Google Nexus 7).

But I have absolutely no idea where to start with this. Is it even possible? What equipment would I need? Would it be affordable?
I already have a router (TP-Link TL-MR3420), to which I would hope to connect the NMEA devices - somehow.

Presumably I would use a device like this (StarTech.com 1 Port RS232 Serial over IP Ethernet Device Server: Amazon.co.uk: Computers & Accessories) to connect the NMEA devices via a serial interface to the network?
Would this alone work, or is something else needed?
How would I then "receive" the data on a computer connected via either ethernet or wifi?

I'm totally lost here, so if anyone can point me in the right direction I'd be very grateful.
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Old 10-11-2012, 07:09   #2
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Re: NMEA via ethernet/wifi

I have an NMEA stream from a multiplexer to a netbook in the nav station via USB. On this netbook, I run NavMonPC, a free program. NavMonPC has many features, but one of them is it will take an NMEA stream on one port, and send it back out on TCP. I set that netbook up with an adhoc wifi network, and connect to it with another netbook used in the cockpit. On the cockpit netbook, you can then tap into the TCP stream either with a TCP enabled application (I use Polarcom/Polarview from Polar Navy) or an instance of NavComPC. That NavComPC can then feed other com port requiring programs with its virtual com ports.

Probably more complicated than you are looking for, but it does work for me! Once set up, it works well.

Chip
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Old 10-11-2012, 07:15   #3
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Re: NMEA via ethernet/wifi

Simrad/Navico just came out with a gadget that will do what you want, although it may not do it in the way you want - I am not sure. It costs $200, but the rub is it works on a N2k network, not 0183. Oh, wait, it only works if you have a Simrad chartplotter I think.

Check out Panbo: The Marine Electronics Weblog to read about it, or go to Simrad Yachting

Chris
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Old 10-11-2012, 10:50   #4
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Re: NMEA via ethernet/wifi

There are plenty of serial to ethernet boxes out there. They are used in data collection often but no vendor comes to mind at the moment. Most are point to point. Google....

The SH combination radios are nice. I would suggest that rather than using a handheld GPS for your source that you buy the SH 50 channel GPS. Then you can wire it to come on whenever the VHF is on and keep the hand held free to roam. (and you do not have to turn it on and plug it in if you want to use the emergency key on your radio)

I use this GPS for the main gps on my boat and with blocking diodes have it so that it comes on whenever I turn on the vhf or ais or chart plotter or computer. I have a dedicated NMEA mux as well to sort out the data streams but the VHF will do that for you too.

The key here is to have a GPS come on when the VHF is turned on so that position data is available without other action.

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STANDARD HORIZON Standard Horizon Smart GPS Antenna at West Marine
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Old 11-11-2012, 18:28   #5
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Re: NMEA via ethernet/wifi

Have a look on eBay with the following search terms:

RS232 WiFi converter

You should be able to find a unit for 50-60$ which will publish the Nmea serial data stream on a dedicated wireless network without requiring any other hardware. Alternatively there are devices for slightly less which will do the same over a Bluetooth connection.

A bit of configuration work is needed to set them up, and you may need to be careful about power supply voltage requirements and NMEA vs signalling voltage levels, but broadly it's a straightforward job to fit one .

Regards,

Mike
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Old 13-11-2012, 04:01   #6
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Re: NMEA via ethernet/wifi

Many thanks for the replies.

SoonerSailor, I can see that what you mention would work great; but for my use case I'm looking for a system where I wouldn't need a computer wired in broadcasting from the chart table - rather I want to be able to move the computer (and tablet and smartphone) around the boat and would just like the simplest (and cheapest) possible base station to transmit over wifi or possibly bluetooth.
Ideally, since I have a wifi router anyhow, I'd like to connect the instruments NMEA outputs to that via ethernet and have them transmitted over my existing wifi network.

The serial to ethernet boxes evm1024 mentions had caught my eye and were what inspired me to finally ask about this topic I've idly wondered about for a while. But whilst I can see how they physically connect the instruments to the RJ45 port of my router, I don't know what the next stage is. How do I access that data from my computer? I assume I would need to install special software which would simulate a COM port on the computer; but does that software exist? More to the point, does it exist for OS X and for Android?
The same question applies with the direct RS232-wifi adaptors mentioned by bluearcus - how do I make that data available to software on the computer, such as OpenCPN?

The serial-bluetooth devices are an interesting alternative, which I hadn't thought of before. But the same question exists; how is that data made available on the computer, to software which is looking for an NMEA stream via a COM port?

Electrically I can, I hope, deal with this, but when it comes down to networking protocols and drivers on the computer, I don't know where to start. I'm new to this side of things really.

I imagine accessing the data on Android devices would be a further challenge, since Android apps are presumably _not_ expecting to see NMEA devices connected to a COM port... but I'll cross that bridge when I come to it; for now let's deal with how it would work with a laptop, and specifically a Mac.

(evm1024 - I'm really asking about how to transfer an NMEA data stream via wifi here, not about simply connecting the GPS to the AIS/VHF, which I do understand. However to clarify, we use the handheld GPS as if it were a fixed one - it is mounted on the instrument panel and wired in, with an external antenna. It is always turned on when the boat is underway. It serves our purpose, at a fraction of the cost of fixed-mounted GPSes.)
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Old 13-11-2012, 04:06   #7
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Re: NMEA via ethernet/wifi

On a side note, evm1024, you mention having a dedicated NMEA multiplexer. Under what circumstances is that necessary? I've always just connected the NMEA devices directly together, and never had any problems.
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Old 13-11-2012, 04:46   #8
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Re: NMEA via ethernet/wifi

Quote:
Originally Posted by Mollymawk View Post
On a side note, evm1024, you mention having a dedicated NMEA multiplexer. Under what circumstances is that necessary? I've always just connected the NMEA devices directly together, and never had any problems.

Mollymawk,

the latest OpenCPN beta version comes with an internal multiplexer including the possibility to send and receive filtered NMEA0183 streams via Ethernet/UDP.

Testing and reporting back would be very much appreciated


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Old 13-11-2012, 10:40   #9
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Re: NMEA via ethernet/wifi

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Originally Posted by bcn View Post
the latest OpenCPN beta version comes with an internal multiplexer including the possibility to send and receive filtered NMEA0183 streams via Ethernet/UDP.
What does this mean, for my use case?
So I can receive NMEA0183 via Ethernet/UDP, but how do I get that NMEA data transmitted to the computer via Ethernet in the first place?

Incidentally, in response to a question I asked on Apple StackExchange (here), I have been told that it would be relatively trivial to connect the NMEA devices to one computer at a time via bluetooth, using a device such as this, since serial-bluetooth adaptors implement the SPP protocol and this is built into OS X (and other bluetooth-supporting OSes, presumably including Android).

However, what I am really looking for is a way to transmit the data over a wifi network so I can access it from more than one device at a time.
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Old 13-11-2012, 10:55   #10
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Re: NMEA via ethernet/wifi

Mollymawk...
That's exactly what was implemented in OpenCPN 3.1.1105 beta. It can receive NMEA from Serial (or virtual serial emulated on USB/Bluetooth) and retransmit it to TCP and/or UDP (Ethernet, wired or wireless does not make a difference)
So the solution is to connect your NMEA devices via serial links to one of your computers which then retransmits the data to the network for use by the other machines.

Pavel
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Old 14-11-2012, 09:47   #11
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Re: NMEA via ethernet/wifi

Yes, I do understand that functionality - and I can certainly see the use in it, and will play with it - but that's not what I'm looking for; I'm looking for the other way around.

My NMEA-interfaced instruments are at the chart table, but the computer isn't necessarily. We don't have a dedicated navigation computer; rather we use various different devices at different times - my MacBook Pro, a Windows laptop, and (hopefully from now on) an Android tablet (Nexus 7).

What I want is a (hopefully cheap) dedicated device for getting that NMEA data broadcast over my LAN so that I can use the data from all those devices. I don't want a computer permanently running at the chart table (I don't have the power for that).
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Old 14-11-2012, 10:10   #12
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Re: NMEA via ethernet/wifi

Mollymawk...
I can very hardly imagine something cheaper than a low power (atom or arm based) computer to accomplish this task. My atom pc with an SSD disk takes about 1A at 12V (without a display of course). The various ARM based boards run at less than 0.5A, but you still have to be pretty knowledgeable to use them effectively.

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Old 14-11-2012, 10:57   #13
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Re: NMEA via ethernet/wifi

Hmm... I do in some ways like the idea of a low-power dedicated navigation computer. I have considered it in the past and I guess I'll probably end up with one one day, but it's not something I'm currently seriously looking at.
I have considered a Raspberry Pi as the basis for a navigation computer; as something basic but relatively cheap and low-power... but on the other hand if I'd rather have something a little more powerful.
As a matter of interest, what do you use? Is it off-the-shelf, or something you built yourself?

Anyway, assuming it were only used for this one purpose it seems like overkill, both from a cost and power consumption point of view. I mean, 1A for a serial-ethernet interface? I'd be hoping for more like 100mA...

It looks like what I'm looking for here doesn't exist, at least in a form compatible with non-Windows OSes - which surprises me as it must surely be relatively simple, and I'm sure there must be a demand for it beyond myself.
Now in an ideal world we'd be looking at an NMEA-UDP (or NMEA-TCP) interface allowing multiple devices on the LAN to read (maybe also broadcast) NMEA data at once, rather than simply a serial over ethernet adaptor. Now, if only I were electronics savvy enough to design one... :-)
(Yes, I know this can be done with a computer; I'm talking about a dedicated adaptor device which does only this.)
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Old 14-11-2012, 11:39   #14
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Re: NMEA via ethernet/wifi

There's always something to learn A RasPi will probably get you as close to your 100mA goal (don't have one to measure) as possible, but it's not powerful enough to be seriously used as a nav station.
You could get even simpler (but not cheaper) with something like an Arduino with ethernet shield, it will be reasonably simple to write something mirroring serial input to net exactly the way you like it, if you know some C. If you want something dedicated to this task, you can buy https://www.sparkfun.com/products/9476 which does it the "hardware" way - note that it costs almost the same as the Raspberry and in reality has quite some electronics inside and takes 180mA@5V which will be almost 100mA@12V counting the loss of a voltage regulator...
What I'm using to build the nav computers are the stock passively cooled mini-ITX boards with either picoPSU or custom built power supplies. If you have enough power to run laptops and wi-fi, you imho also have enough to run one of these...
If you want to experience some ARM adventure, mk802 v2 is the device you want to have a look at - has more power than the Pi and costs way less than a Beagle or Pandaboard.
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Old 14-11-2012, 12:03   #15
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Re: NMEA via ethernet/wifi

Hey this stuff is pretty similar to AppleTalk.
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