NMEA output

[doug748]

I want to get my plotter (Digital Yacht) to share information with a Sounder/Log (Echopilot).
Here is a snatch of the diagram showing the general method:

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(Please ignore the pencil annotation)
The area of interest is marked "GPS Instrument". It shows two outputs one:
NMEA Out +
one:
NMEA Out -
The manual (as I read it) seems to suggest that some units only have one NMEA output (+) and if that is the case, I must connect the negative pole of the battery to the - NMEA input of the sounder/log instrument.
Can the electronics literati confirm this? Does it make electronic sense?
In case I have not already given the game away, I am clueless.

 

[nimbusgb]

Yup that's right. it's not strictly correct but it generally works.

 

[doug748]

Thanks nimbusgb.

I have connected things up but its not working. Any other general observations are welcome. I like to get as much background as possible before getting onto the helplines - Is there an easy way of testing a NMEA output?

....How do we pronounce it? N.M.E.A. Neeema?

 

[mjcoon]

Thanks nimbusgb.

I have connected things up but its not working. Any other general observations are welcome. I like to get as much background as possible before getting onto the helplines - Is there an easy way of testing a NMEA output?

....How do we pronounce it? N.M.E.A. Neeema?

I haven't chatted about it much, but think you have to pronounce all four letters...

The other variation is that there are old and new versions, NMEA-0183 vs NMEA-2000. Wikipedia says: "An NMEA 2000 network is not electrically compatible with an NMEA 0183 network" so you need to know which your devices use.

HTH, Mike.

 

[timbartlett]

Thanks nimbusgb.

I have connected things up but its not working. Any other general observations are welcome. I like to get as much background as possible before getting onto the helplines - Is there an easy way of testing a NMEA output?

....How do we pronounce it? N.M.E.A. Neeema?

NMEA is the National Marine Electronics Association (of America). Their big-wigs get quite aerated if you pronounce it "Neema", but almost every marine electronics person on thisside of the Atlantic does.

There are several NMEA protocols, but the only two you are likely to come across are NMEA0183 and NMEA2000 (sometimes abbreviated to NMEA2k) The Echopilot and the Digital Yacht plotter both use NMEA0183

The key feature of NMEA0183 is that it is a one-way system using two wires.

One instrument is the "Talker": the other is the "listener". (In practice, up to about five listeners might be able to listen to each talker, but let's no go there for the moment.)

You need to connect the Output positive of the talker to the Input positive of the listener,
and the Output negative of the talker to the Input negative of the listener.

To achieve two-way "conversation" both devices need to have both an input port and an output port: you connect the input port of one to the output port of the other, and vice versa.

It is confused by the fact that there is no standard colour coding or terminology:-
Outputs are sometimes labelled Tx, and inputs are sometimes labelled Rx
Positives are sometimes labelled "signal"
Negatives are sometimes labelled "common" or "return" or "ground"

The principle, however, is simple:-
Connect output to input
Positive to positive and negative to negative.

In the case of your Digital Yacht, I think the "negative" (for everything except power) is green -- but check with your manual!

The bit many people forget is that a lot of instruments require you to switch the ports on -- it is usually buried in a set-up menu somewhere -- and to make sure that they are speaking the same language at the same speed.

If you want to check that NMEA data is being transmitted, put a voltmeter across the Out+and Out- wires -- a fluctuating voltage of between 0 and 5, averaging about 2-3 suggests that NMEA data is being transmitted.

Good luck.

 

[doug748]

Thank you Mike, and Tim your answer is a touchstone of clarity.

I have fiddled with the output settings and feel that is ok, ditto the NMEA export sentences.
I think the green (common) on the plotter might be a clue, in place of the black battery neg I have connected at the moment (hope I have not blown the thing up). I shall ring up Digital Yacht for confirmation when they all get back form the Boat Show -}
Thanks for the testing tip.

 

[mcframe]

If you want to check that NMEA data is being transmitted, put a voltmeter across the Out+and Out- wires -- a fluctuating voltage of between 0 and 5, averaging about 2-3 suggests that NMEA data is being transmitted.

Thanks Tim - that's a great "Why didn't I think of that?" debugging trick.

 

[nimbusgb]

Usually pronounced 'Nem-e-ah' frequently pronounced 'nema'.