rbtnt

I am looking for the difference in two GPS interface specs. I have had 4 different Garmin handheld GPS units that I used to run my Livorsi analog GPS speedometer. My latest Garmin GPS (GPSmap76) has a different NMEA output format than my previous units and is not compatible with my speedometer.

The older GPS units were set up to output NMEA 183 Ver 2.0 and the new one will only output NMEA 183 Ver 2.3. My older GPS' even had the option to select one of several NMEA versions to output. Does anyone know what the difference is in the two versions? I have looked all over for the specs.

I'm glad I don't have a lot of electronics running off this unit and I wish I hadn't sold all the other GPS'.

Garmin said tough luck and I have not heard back from Livorsi to see if they have an update.

I guess the worst case would be to buy another handheld just for the speedometer or buy one of Livorsi receivers.

The Menace

I have several Garmins but when it comes time to hook up to the GPS speedo in your boat everyone suddenly has a memory lapse of technology. Nobody assured me that the Speedo would be compatible.

I do not know the difference either, however I have found the best source of information has been the people at Boat US.

If I ever get any quality info I will pass it on. Good luck.

rbtnt

Here is what I have found so far:

Livorsi GPS will accept NMEA 0183 Ver 2.0 through ver 3.01 at 4800 baud

Garmin 12XL GPS outputs NMEA 0183 Ver 2.0 (worked great)

Garmin GPSmap 76 outputs NMEA 0183 Ver 2.3 ( I haven't got this working yet, but I have a few settings to try that are not in the manual).

If this doesn't work, I will borrow a 12XL and run the data into hyperterminal and see what it looks like compared to the GPSmap 76. If it is different, there is nothing I can do about it.

rbtnt

Still not working.

Here is what I found using Hyper-Terminal.

The 12XL outputs the speed in a fixed length field of XXX.X.

The 76 outputs the speed in a variable length field with a minimum size of X.X. I guess would be that it will work at speeds about 99 mph. With the refresh on the motors and all the rain and swollen rivers around here, I haven't been able to run much this year, much less 100 mph passes.

It doesn't look like the Livorsi speedometer can read the variable length speed field.

Does anyone know if the NMEA 183 ver 2.3 defines the speed field in the GPRMC statement as a fixed length or variable length field?

rbtnt

Another update:

I talked to Livorsi today and they confirmed that my problem was the format of the velocity data. Now the good news, they have an update for my speedometer for $65 with a 1-2 day turn around. My speedometer is more than 3 years old and was one of the first ones available.

I'm sending it to them tomorrow. No big hurry, with the rain we had the past 3 days the river will not be usable for 2 weeks.

My speedometer continuously moves from 0 - 30 and back.

rbtnt

The GPS speedometer is fixed. Livorsi tuned it around in one day and the update fixed the problem.