N2K

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Steve Bourne

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Jan 21, 2021, 3:10:11 PMJan 21
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Has anyone looked at taking N2K sentences as input and output them as NEMA-0183.  

Steve

Jim Starkey

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Jan 21, 2021, 3:19:53 PMJan 21
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Problematic.  Even if N2K had been completely reverse engineered, there would still be a bandwidth problem.  NEMA-0183 has barely enough bandwidth for GPS; Garmin fast GPSes require cranking NMEA-0183 up to 9.6K baud, which is both non-standard and not supported by more peripherals.  AIS sentences, sent at 38.4K baud, would be a disaster.  And even if you cranked NMEA-083 up to 38.4K baud across the board, I doubt that many devices would accept it.

NMEA-0183 sentences over UDP is a de facto standard.  OneNet (NMEA over IP) is N2K sentences over UDP but almost certainly with a crypto handshake to keep non-NMEA licensees from tapping in.


On 1/21/2021 3:10 PM, Steve Bourne wrote:
Has anyone looked at taking N2K sentences as input and output them as NEMA-0183.  

Steve
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Teppo Kurki

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Jan 21, 2021, 3:35:36 PMJan 21
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Signal K server can convert NMEA2000 to Signal K and Signal K to NMEA0183. It can also do the reverse.

Conversion to NMEA0183 can be activated and throttled per sentence. On my boat I use this to convert GPS data from N2K plotter/mfd to my DSC VHF that has 4800 baud 0183 input.



On Thu, Jan 21, 2021 at 10:10 PM Steve Bourne <srbo...@gmail.com> wrote:
Has anyone looked at taking N2K sentences as input and output them as NEMA-0183.  

Steve

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Jim Starkey

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Jan 21, 2021, 4:12:57 PMJan 21
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And it only costs $300!

A $10 GPS dongle, a $10 USB to RS-232 dongle, a $35 Raspberry Pi, and a tiny bit of programming and you're done.  Find a dozen other useful things to keep the Pi amused shouldn't be hard.

Steve Bourne

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Jan 21, 2021, 4:22:23 PMJan 21
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Thanks for the links and suggestions.  

Steve

Teppo Kurki

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Jan 21, 2021, 4:33:42 PMJan 21
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On Thu, Jan 21, 2021 at 11:12 PM Jim Starkey <j...@jimstarkey.net> wrote:

And it only costs $300!


Was this a joke? If not what on earth are you talking about?  

Jim Starkey

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Jan 21, 2021, 4:58:53 PMJan 21
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https://digitalyachtamerica.com/product/ikommunicate-nmea-signal-k-gateway/

Perhaps I've missed something.  Last I heard, the agreement between Signal K and NMEA was that NMEA would bless Signal K as long as a NMEA licensee produced the box.

There are two sticking points.  One is a CANbus (N2K) / USB gateway.  These are in the range of $200.  And that's for the hardware, so you're not out of the woods yet.

But then, again, I may have missed something.  But intellectual property issues aside, CANbus is extremely computer unfriendly and doesn't have the bandwidth to transmit a radar image, chart, sonar image, or any form of video, so I very little interest in it.  My boat has Seatalk instruments, 183 links between autopilot and chart plotter, wired Ethernet between chart plotters and radar, Ethernet between masthead WiFi router and an RPi functioning as a wireless router, WiFi from a Raymarine E7 to iOS devices, two Seatalk / 183 / rs-232, etc.  In short, a mess.  I want a single Ethernet/WiFi network with enough bandwidth to keep everyone happy.  N2K will never be in the picture.

If you want a cheap GPS data source, a couple of dongles and an RPi is by far the way to go.  And it it has Ethernet.

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Alan Hails

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Jan 21, 2021, 5:02:40 PMJan 21
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Jim, I accept 38.4K baud NMEA 0183 sentences for AIS plus GPS from my Standard Horizon DSC VHF radio into my boat's Beaglebone Black running OpenCPN via a serial-to-USB 2.0 4-port hub.  I'm able to use that to navigate plus display and target query AIS contacts, plus output that data to my B&G Network instrument system on a 2-way 0183connection at 4800 baud, no problems.  That also makes the AIS, GPS, and wind, depth heading, speed, water temp., etc. data available to KPLEX where I broadcast it over 802.11N wi-fi to my home network where NavMonPC running on a Windows 8.1 PC accesses it for remote display and logging.

Alan Hails
S/V Scotch Bonnet, Pearson 39-2
PHRF Non-Spinnaker Class Rating 132
Cell: 941-323-0661


Jim Starkey

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Jan 21, 2021, 5:05:22 PMJan 21
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That's fine as long as you keep the AIS gook off the 4kb links.  But the original question was about N2K.

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Alan Hails

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Jan 21, 2021, 5:09:09 PMJan 21
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Yes, Jim, and one of your incorrect statements is that 38.4K Baud NMEA 0183 data is useless, cannot be accepted by other devices, and AIS at that rate would be a disaster...

Alan Hails
S/V Scotch Bonnet, Pearson 39-2
PHRF Non-Spinnaker Class Rating 132
Cell: 941-323-0661

Jim Starkey

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Jan 21, 2021, 5:18:56 PMJan 21
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What I said is that many devices, chart plotter for example, won't take regular 183 data off a 38.4 kb connection.  I haven't tried it, but Raymarine says it doesn't work, at least on the E wide series; the "high speed" serial port can be either general 183 at 4kb or dedicated AIS at 38.4 kb.  And I said that AIS sentences on 4kb links would be a disaster, which if you look at the sentence length for AIS messages and the total lack of flow control on 183, should be obvious.    AIS is intended to work at 38.4kb.

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Keith Young

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Jan 22, 2021, 7:27:24 AMJan 22
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To address the original question...there are a couple of parts to this.  Reading data from canbus and converting those data to NMEA-0183.  kplex supports neither of those.  The easiest way to feed N2K into kplex is through an N2K to NMEA-0183 converter like the the Actisense NGW-1.  Plug one end your N2K network, the usb into your raspberry pi or whatever, configure up another serial interface in kplex, job done.  But at a cost of €140.

Kees Verruijt's canboat software was the first open source project I know of to make significant inroads into translating N2K PGNs into NMEA-0183.  You still need to get the PGNs off of canbus which you can do with something like the Actisense NGT-1, but if your only purpose is to convert to NMEA-0183 you may be better off with acquiring the NGW-1.  Kees is a major contributor to SignalK (as referenced by Teppo above).

Timo Lappalainen has done a lot of work with using arduinos to read n2k from can.

Google will yield plenty of results on the various can interfaces now available for the raspberry pi.

Having seen some open source seatalk-1 converters which completely disregard collision detection and avoidance I confess I would be more hesitant with non-nmea-certified devices *writing* to canbus than reading from it.

To address some other points in this thread, the confusion Teppo had with Jim's "$300" statement was that the "NMEA approved" way of translating N2k->SignalK is via an approved gateway, and the iKommunicate is not cheap.  However SignalK" is free (and with openplotter, easy) and conversion is possible using non-NMEA-certified can boards which cost a lot less than those with a NMEA badge.

To randomly address another point...Jim if Raymarine told you (apologies in advance if I have misinterpreted) that non-AIS sentences wouldn't be recognised on a 38.4k link I'd take that with a pinch of salt.  There would be no reason to implement it like that and at least some of Raymarine's own AIS units have multiplexers built in which I believe will combine 4800 input (typically DSC) with AIS  and send everything out at 38.4 to an attached MFD.  Unfortunately lockdown prevents me from getting to my boat to experiment with my C90W which should presumably be no more capable than your E series wide

Jim Starkey

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Jan 22, 2021, 11:28:13 AMJan 22
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I've checked the Raymarine documentation and it appears that most of their chart plotters will accept general NMEA 0183 data on a port set to 38400 baud, though historically only support one port for that baud rate.

The reason that a device might not support general NMEA 0183 as processing AIS data is radically different from other sentences in that AIS messages are broken into multiple sentences, are ASCII encoded compressed binary.  And since the first character gives it away, there is no logical reason that any NMEA 0183 parser can't handle both, but remember we are dealing with software engineers that preferred to use speed through the water rather than speed over the ground for computing true wind direction.  But we can hope they have since gotten smarter.

The getting back to the original point, I submit that a dedicated GPS is a hell of lot cheaper than trying to tap GPS data from N2K.

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Keith Young

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Jan 22, 2021, 12:57:44 PMJan 22
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On Friday, January 22, 2021 at 4:28:13 PM UTC James Starkey wrote:

but remember we are dealing with software engineers that preferred to use speed through the water rather than speed over the ground for computing true wind direction.

We're getting into a whole different discussion (and one which has been done repeatedly on other forums) but the problem you're talking is, I believe, about naming ambiguity rather than usefulness of the data.  "True Wind" is relative to the medium beneath you, ie the sea.  Wind calculated relative to the ground (ie using SOG) is termed "Ground Wind" by some manufacturers.  Is "True Wind" a misleading term?  Probably (see the number of times this gets discussed on sailing forums!), but before GPS they didn't have the option of calculating anything else.  When sailing "True Wind" is vastly more  interesting to me than "Ground Wind" because we don't sail in the "Ground Wind".  If I have 2 knots of breeze and 2 knots of tide in the same direction there's nothing I can sail in :-).  You can argue "ah but the tide turns" but I can factor that in to longer term plans as a small increase / decrease in wind strength and slight change in direction.  In practice I sail with the wind instruments on apparent and do a very rough conversion to true in my head if I want to know what the wind will be like if I change speed / direction.

Teppo Kurki

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Jan 22, 2021, 2:01:59 PMJan 22
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On Fri, Jan 22, 2021 at 6:28 PM Jim Starkey <j...@jimstarkey.net> wrote:

The getting back to the original point, I submit that a dedicated GPS is a hell of lot cheaper than trying to tap GPS data from N2K.

If this was a reference to my "N2K GPS to 0183 for the VHF" use case: not if you already have all the pieces in place, like I had. LIke you said, usually a standalone would be cheaper. But that is not what the original question was about.

On Thu, Jan 21, 2021 at 11:46 PM Steve Bourne <s...@acm.org> wrote:
Looks perfect.  What do you run it on.

Most people run it on a Raspberry Pi, but almost any computer with Linux, MacOS or Windows will do.
 

Ken Harris

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Jan 22, 2021, 10:22:11 PMJan 22
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On Thu, Jan 21, 2021 at 1:58 PM Jim Starkey <j...@jimstarkey.net> wrote:

> There are two sticking points. One is a CANbus (N2K) / USB gateway. These are in the range of $200.

http://canable.io is $29

> CANbus is extremely computer unfriendly

Not in my experience. Why do you think CANbus "extremely computer unfriendly" ?
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