Smartcraft Speedometer compatibility with NMEA 0183 version

[greauxpete]

What is the highest version of NMEA 0183 compatible with sending speed data to the Smartcraft Speedometer?
(My new Garmin unit sends out version 3.1)

[EuropeanAM]

I seem to recall that it was Version 1.8 (though my understanding is that it was updated in the base software since then, with no mention of the actual version number).

Need to be careful to eliminate any unnecessary sentences, and keep the baud rate low (see FAQ Section, there is some info on this).

[greauxpete]

I have not found a solution to my smartcraft speedometer not reading speed yet, but im a step closer to confirming a nmea 0183 signal is being output through the garmin (nmea 1txd) blue wire and ground.

I powered the garmin 741xs unit in simulator mode and assigned a random simulator speed of 12 mph.
I powered it up using an 18 volt cordless drill battery at home, by attaching the red to the positive on the battery and black to negative on the battery.

Next, while still in simulation mode, I used a voltmeter
and measured the voltage between the garmin blue (NMEA 1TXD) wire and the black ground. Garmin states that you should observe a voltage between 0 - 5 volts every 2 seconds.
I did in fact observe the voltage varying between 0-5 volts. So, I have confidence the garmin unit is doing its job. Now, i can troubleshoot the boat wiring (ground in particular). If there is still an issue, I think it may be the nmea 0183 version incompatibility issue.

I wanted to bring up the simulator mode test, so in the future others can test gps to speed units with the boat parked (not moving, no buddy required).

[greauxpete]

After testing the nmea 0183 voltage on the boat wiring using jumpers with alligator clips, I am getting an nmea signal with a variation in voltage in simulator mode but, no speed data on the smart craft speedometer. I even tested it with the drill battery powering the gps, so I could make sure the ground was solid but no joy. I have all of the sentences turned on.
Any other reccomendations?

Here are the sentences I have on:

20210121_164835.jpg

20210121_164821.jpg

I suspect an nmea 0183 compatibility issue.Next step is testing with an old gps which I have confirmed uses nmea 0183 2.0. Ordered an nmea output cable.

[greauxpete]

After testing with the old small gps unit (Eagle 350S/MAP) with nmea 0183 ver 2.0, the gauge speedometer works (needle was at 11mph simulator speed).
Therefore, now i know my basic wiring and gauge calibrations/setups are correct.

I was able to test the voltage output on the eagle unit with voltmeter prior to testing since I did not have a data cable.
I used jumpers with alligator clips to determine which pins were outputting voltage.
The voltage output was higher on the eagle unit than it was on the garmin unit, perhaps due to version incompatibility.

[EuropeanAM]

Not really easy to determine data stream version or information based on "voltage tests".

You also need to make certain that you have the appropriate "battery ground" connected to one of those leads (see info in the FAQ Section on NMEA-0183 connections).

[greauxpete]

Thanks for reviewing it Don.

I'm pretty sure my ground is correct as I have it wired as follows:

Garmin "Blue" (Tx OUT) to Smartcraft Speedo White
Garmin "Black" (ground for both power and NMEA 0183) to Smartcraft Speedo Blue
(Unit turns on and nmea 0183 voltage signal is ouput from the blue and black garmin wires, Tried reversing the wires as well)

Garmin confirmed the 741XS outputs NMEA 0183 Version 3.1, so the NMEA 0183 "version" compatibility seems to be the issue.
(Unless someone has had success with this model)

Looks like I will just need to get a 12 volt powered GPS receiver/antenna which outputs NEMA 0183 version 2.0 or use my old eagle unit to transmit gps speed.

[EuropeanAM]

Did you look over this thread, and note the wiring shown has both the (-) NMEA0183 lead AND a 12V ground tied in?

http://www.bbcboards.net/showthread.php?t=60875

[greauxpete]

Yes, I even confirmed the ground using a full size stand alone battery (right at the console to eliminate wiring anomalies) and grounded everything with jumpers to the negative post.
I contacted Garmin about minimum sentences and number of decimal points digits in garmin nmea 0183 output for various versions. A lot of trial and error, but no success.

In the mean time, I ordered an external gps receiver (sierra 68982P) and after temporarily powering
it up last night and connecting to the smartcraft speedometer, the heading (degrees) and speed
(moved gps antenna around to get 1mph to show up) were picked up by the speedo
(the gps antenna even picked up a gps signal in a metal building).

The smart craft gauge is not the problem.

I hate to give up on the garmin output, but im at the end of my rope.
I learned alot about nmea 0183 in the process , so it wasn't all for naught.

I think I have an acceptable solution going forward. Hope this helps someone.

[EuropeanAM]

Glad you found a solution that worked for you. Do keep in mind that on that ground- the ENGINE and the GPS and the GROUND all need to be on a COMMON battery.

[greauxpete]

Ahh.. that is probably my issue since I have a dedicated engine starting battery and a dedicated "house battery" with a blue sea SI-ACR (start isolation - automatic charging system).
The Garmin GPS is wired to the "house" battery so they are indeed different battery grounds.
I'll see how this works out and if I have issues I may tinker with my grounds to the Garmin unit.


I wired the sierra GPS receiver to the starting circuit since I only want it on when the engine is running.'

Thanks for the help..

[EuropeanAM]

Check your battery compartment. There should be a common GROUND battery cable connected between the house battery and the cranking battery, also.

[greauxpete]

OK Thanks!