GPS/Electronic Help please

[ianwright]

I have a Garmin 120XL connected to a Yeoman paper chart plotter, at the chart table and working well. I also have a newer Garmin 128 bought as a spare.
What I'd like is to keep the system I have and/plus/also use one or other gps in the cockpit such that the gps's and the Yeoman talk to each other.
Can it be done? Can it be done by me? Will stockholm tar and some fancy knots help?
Advice from one who knows this stuff please.

IanW /forums/images/graemlins/confused.gif

 

[Robin]

First question is why link the 2 GPSs together? Why not run the 2nd one out in the cockpit (assuming it really is waterproof) as a standalone set, from a separate battery would be even better. The only downside I can see is that the cockpit GPS would not then run the Yeoman if the first set fails, but then that is no real hardship short term. You could always run a separate NMEA lead from the second GPS to the Yeoman ready for use but not connected until/if needed, or even ready connected via a changeover switch.

 

[bonny]

If you are using NMEA to communicate between items then the answer is probably no.

GPS's are NMEA talkers, your plotter will be an NMEA listener (to gps) and an NMEA talker (to an autopliot) through a separate connection.

You cannot connect more than 1 GPS NMEA o/p together because they will talk all over each other.

If your intention is to be able to use each of the GPS's to talk to your plotter then this can be done provided only 1 of the GPS's is connected at a time. You could connect all the GPS NMEA- terminals together and use a switch to select between each of the GPS's NMEA+ terminals into the plotter. This would allow you to manually choose which of the GPS's the plotter gets it's position from - offering GPS backup is one fails.

If you really want all the GPS's connected you would need to use an NMEA multiplexor/combiner costing over £100.

 

[Birdseye]

Even with a multiplexer, your Yeoman would be getting feeds showing different positions arising because of the inaccuracy of GPS. OK the differences would not be great but could well be enough to cause problems.

Why not just get a GPS repeater?

 

[Mariner]

Some multiplexers will filter the sentences from the second gps. If the first gps stops transmitting data the multiplexer will then send the data from the second gps.
A multiplexer is a really simple way (if expensive) way of connecting equipment together.

 

[Marsupial]

Other things to consider - your Yeoman is not only a listener, it sends waypoints to the GPS via NEMA.

The best way to go IMHO would be mount both GPS systems such that they could be easily connected to the NEMA "spine" with simialr plugs and sockets (but only one at a time), and have a repeater in the cockpit permanently connected to the NEMA "spine". That way all you would loose would be the waypoint information and routes in the GPS should the "main" unit fail, after plugging in the bac-up GPS you could still automatically plot with the Yeoman.

 

[ianwright]

Oh bugger! I suspect I have asked a question the answer to which I am not equiped to understand. /forums/images/graemlins/frown.gif

Let's try again, be gentle with me,,,,,,,,
The Yeoman Handbook gives the same connections for both the 120XL and the 128.
I now intend (for intend read hope) to replace the (old)120XL with the new 128. That’s easy, the connections to the Yeoman are made. I just need to unplug the power and data plus aerial from the 120XL and plug in the 128, set the NMEA to 0183 1.5 4800 baud and bob’s your uncle, the system should work,,,,,,,,,,,,,,,,
Now I need to connect the old 120XL in the cockpit , I assume without an aerial (?) so that I can use it as a repeater (?).
Am I stepping into electronic goo again?

IanW

 

[tome]

Ian

What you propose will work fine, but you will need an antenna in the cockpit for the second GPS. It won't function as a repeater.

 

[philip_stevens]

Tome,
I think that the second GPS could get position information, ets., via NMEA from the main GPS. At least that is how it sounds in one of my GPS manuals.

 

[pvb]

Not sure Garmin works that way...

Garmin kit tends to have to be set up quite precisely for interfacing. If you want to interface one Garmin with another Garmin, you usually need to select a "GRMN/GRMN" interface. However, if Ian wants his 128 to drive the Yeoman, presumably the 128 will have to be set up to interface via NMEA. So I don't think the old 120XL in the cockpit could work as a repeater.

 

[philip_stevens]

Re: Not sure Garmin works that way...

yes, that makes it clear to me with regard to Garmin.

I have 2 AP-Philips GPS - a semi-waterproof Mk8 in the cockpit, and a Mk6 in the cabin. The Mk6 has 2 separate outputs that can be set to 0180 or 0183. This feeds the radar, that won't read the Navman 5500 Plotter. The plotter feeds the Autohelm interface/Autohelm ST3000, and the Yeoman Plotter.

I wanted two GPS in the cabin at charttable, but also a repeater in the cockpit. Getting hold of an old Mk8 sorted that out, as well as being completely independant of the cabin GPS.

A bit over the top, but whatever. That's what being an electrician does......

 

[tome]

With a single interface port, GPS has to be set to NMEA for the Yeoman, see pvb's reply. This means it cannot also be used to feed a repeater, which is a good thing as the 2nd set now provides GPS redundancy against all but power failures.

 

[philip_stevens]

Had all 3 working yesterday when I went on the boat to do some more electrical tidying-up. All 3 were within 3/100ths of each other on Lat and Long. A good check. Even got GLL on the radar display.

I am not sure what version of 0183 the Mk6 outputs, but the radar would not read the 0183 from the Navman 5500 - on the same connections that feed the Autohelm.

For anyone is interested in all (or just about all) NMEA sentences, go to http://pcptpp030.psychologie.uni-regensburg.de/trafficresearch/NMEA0183/types.txt
or
http://snipurl.com/cay7

regards,
Philip

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