NMEA strangeness from Garmin 60C GPS - SailNet Community

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  #1  
Old 07-27-2010
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NMEA strangeness from Garmin 60C GPS

I have a Garmin 60C GPS which I have tried from time to time to interface with a DSC VHF radio or Raymarine wheel pilot but the other devices act as if no NMEA sentences are being sent.

I've tried it with a Raymarine 54 VHF, S1 Wheel pilot, and a Standard Horizon Matrix VHF and none of them recognize the Garmin GPS.

But when I connect the 60C to my laptop, it happily connects as expected at 4800 baud and both OpenCPN and Google Earth can recognize and use the NMEA input just fine.

I've tried *three* different Garmin cables, and two of them were also tested with my old Garmin 12XL and work just fine, so the problem isn't the cable or the connections. Unplugging the 12XL, which the VHF and autopilot recognize and plugging in the 60C still fails to work.

Here is an extract from the NMEA output from the 60C:


$PGRMZ,198,f,3*1B
$PGRMM,WGS 84*06
$GPRTE,1,1,c,*37
$GPRMC,084020,A,6013.3447,N,02445.3195,E,0.0,163.3 ,210710,6.8,E,D*15
$GPRMB,A,,,,,,,,,,,,A,D*0E
$GPGGA,084020,6013.3447,N,02445.3195,E,2,10,0.9,60 .4,M,19.7,M,,*73
$GPGSA,A,3,03,05,06,07,08,10,15,19,,26,28,,1.8,0.9 ,1.5*3A
$GPGSV,3,1,12,03,17,031,46,05,41,233,50,06,11,018, 37,07,41,081,51*7E
$GPGSV,3,2,12,08,79,109,52,10,20,197,45,15,27,295, 48,19,22,060,46*70
$GPGSV,3,3,12,21,13,328,34,26,44,290,49,28,45,165, 48,33,14,225,43*75
$GPGLL,6013.3447,N,02445.3195,E,084020,A,D*45
$GPBOD,,T,,M,,*47
$GPVTG,163.3,T,156.4,M,0.0,N,0.0,K,D*27
$PGRME,1.9,M,3.0,M,3.6,M*20
$PGRMZ,198,f,3*1B

I'm wondering if it is a versioning issue. Perhaps OpenCPN and Google Earth support a broad range of NMEA versions and the VHF and autohelms I've been trying to interface with don't. But certainly the old Garmin 12XL has a much older version of NMEA, so why would it work where the 60C would not?

I'm left scratching my head.....

Any NMEA gurus with some insight?
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Old 07-27-2010
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If I am correct they are Garmin specific strings, you have to change the output to NMEA before it will be recognized, is your menu options allow it.
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Old 07-28-2010
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Quote:
Originally Posted by r.furborough View Post
If I am correct they are Garmin specific strings, you have to change the output to NMEA before it will be recognized, is your menu options allow it.
The output is set to NMEA IN/NMEA OUT and both OpenCPN and Google Earth recognize and work fine with the NMEA that the 60C is providing, and it's definitely at 4800 baud. The problem is with the VHF and autopilot. Neither seem to "see" the GPS at all.

It's not the cable or connection because the Garmin 12XL uses the same cable and pinout, and both VHF and autopilot see the 12XL and work fine.

That's the mystery. It seems to be outputting NMEA just fine, and the connection to the VHF or autopilot should be just fine, but it just doesn't work.
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Old 07-29-2010
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Looking at the GPRMC sentence, I can see the final value is a D (before the checksum). This indicates NMEA 2.3, according to this website, since that field didn't exist before that version. You may be correct that it is a versioning issue, since I think the extra field would cause the checksum to be miscalculated if the receiver wasn't aware of it. I have been unable to find any info about when NMEA 2.3 was introduced. If you can, try to figure out what version of NMEA all your devices support. Your GPS may have an option to output in 2.0 compatibility mode.
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Old 07-29-2010
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patrick, I'm glad to know someone else still has a 12XL in working order. But even with that--as rm suggests, the exact sub-version of the NMEA can make a total difference. If the equipment doesn't specifically list the exact same versions for both devices, there is no reason to expect them to work. Just one "decimal point" difference in the NMEA versions is enough to gag some equipment. Other times, you can tell your GPS to use different versions and one of them may work anyway.
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Old 08-26-2010
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You connected the 60C to the computer with the serial cable and not USB? My 60CS will output NMEA via the usb cable, but the 4-pin connector on the GPS appears to be broken. It powers the GPS ok, but I get nothing on the NMEA out. Tried connecting an oscilloscope to it and nothing is coming out. Got a new 76Cx from west marine for $180 and it works fine. I wonder if the old 60C series has a problem with the NMEA breaking, or if there is something funny with it that lets it work with a computer but not common marine equipment. Like the NMEA in on the unit need to be connected to see anything on NMEA out.
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Old 08-27-2010
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Quote:
Originally Posted by tap View Post
You connected the 60C to the computer with the serial cable and not USB? My 60CS will output NMEA via the usb cable, but the 4-pin connector on the GPS appears to be broken. It powers the GPS ok, but I get nothing on the NMEA out. Tried connecting an oscilloscope to it and nothing is coming out. Got a new 76Cx from west marine for $180 and it works fine. I wonder if the old 60C series has a problem with the NMEA breaking, or if there is something funny with it that lets it work with a computer but not common marine equipment. Like the NMEA in on the unit need to be connected to see anything on NMEA out.
That's a good point. I have a multiplexer somewhere that I might try to put in between the GPS and the autohelm. It may be that the line voltage levels are not quite what they should be and the laptop (or the serial to USB adapter) is able to deal with it but not the VHF or autohelm.

Supposedly the multiplexer also is meant to provide amplified NMEA signals so maybe that will resolve the issue.
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