NMEA <-> RS232

[Doghouse]

Ok I want to hook my computer up to the NMEA output from my GPS.
Can I just use the NMEA in/out wires?

I am looking for the downstream of coordinates more than the upstream of routes.

tnx

[Alan Wheeler]

Yes you just hook up those wires. what Data is sent/recieved is controlled by the Units. You want to get into the set up of both and turn on and off what you need to be sent and recieved. You may need some help from the manuals to see what is required and the exact language being used.

[Doghouse]

Tnx, I found it is 2,3,5 pins. 5 being ground. if that does not work, swap pins 2,3.

[Pblais]

Dog,

I think you have it. You can add three listeners to one talker without the potential of problems. Note 4800 bps no parity, and one stop bit. You are home free.

[Alan Wheeler]

Arrrgh, that last part makes me angry about getting stuff to talk to one another. Why can't they just keep it simple. I don't think I have eve yet found a manual that explains all that stuff.

[Pblais]

Well RS232 is pretty simple. I just remeber 8-None-1 as that is the default for a COM port setting on a PC. You genrally can get by without pin 5 the signal ground and the 2 and 3 transmit receive can be easily switched if you get them wrong. So it's not that hard.

I set up a bus bar for 2 and 3 coming off the GPS and then route to the RS232 laptop, the Furuno display and the Auto pilot. One GPS can feed three devices. You might get a 4th depending.

Soon we will see the new NMEA 2000 stuff. This is a network basd interface and we can chuck serial ports but with Ray Marine doing their own thing it may not really be much of a standard.

[ronbo1]

What if you don't have a 9-pin serial port on your computer, just a couple UBS
ports?

[Pblais]

You can get a USB to serial adapter.

This is a good web site for them with some good discussion:

http://pfranc.com/projects/g45contr/g45_idx.htm

The sell the cables but also sell the good pfranc USB to serial cconverter cables. You can search the web and perhaps get a better price for the same units but these really are the ones to use for no hassles. Don't use the cheap ones as you may find they suck. These are about $29 and work quite well and have nice led light indicators. Well made.

They also sell Garmin cables as well and those are nice if you get them premade.

You also install the driver that comes with it and you now get a COM port 4 you can use like a real serial port. Most laptops don't have serial ports any more. I use one with mine as my old laptop is no longer sea worthy. The Admiral says we need to be able to watch DVD exercise videos. That computer is also faster for the vector charts too.

[Antares]

The ubs/serial adaptors work. I went from the RS232 9 pin on my original laptop to the serial/UBS conversion for the new one and it was painless. Just load the software and go.

The entire set up has Furuno depth, Garmin GPS, and Sail Comp compass talking and the Furuno depth, Raymarine radar, Simrad autopilot, Skymate email and Ockam instruments listening as needed. A couple of terminal strips sort it out. The laptop communicates with the GPS. Next is a multiplexer to simplify the talk into a single stream. I'll save that until it is required. On the output side, the gps is used by most of the listeners. So far is has sufficient signal strength to keep everyone happy.

It took some time with each manual and several sketches of the wiring to get it all to happen, but by adding one component at a time to the mix to establish communication, it worked out. The big leap of faith was accepting the Garmin GPS uses DC ground as the NMEA return. If anyone is interested, I can share my schematic.

[AnchorageGuy]

Antares, I would much like to see your schematic.

[hglad]

Antares: Would appreciating seeing your schematic.
HGLAD

[Antares]

Yikes! I looked at my schematic and I had better cover the process used to develop it.
First you must spend some quality times with the manual for each piece of equipment. I recorded NMEA version(s), sentences sent and received, ie (BWC, DPT, WPL, etc). This let me know from the get go if the talkers said what the listeners needed to hear. The versions gave me indication if the dialect and signal was the same. I have interfaced some older equipment so version can be a factor. If the correct sentences are available you are on your way. If they are not, then you are proceeding with a chance of being frustrated, but you will know why.

Next is diagramming each unit’s basic wiring information. Color and function is what you need to know. With all this you can diagram a schematic as to which wires get connected. Without a multiplexer or a unit that can take listen to more than one talker, you can only a single listener can only read from one talker. One talker can talk to more than one listener so some prioritizing may be in order. From here, the physical layout can be determined. The location of terminal strips, wire runs and computer connections are set and the pieces installed.

I started testing with the GPS talking to the PC, this allowed a check of the output sentences. Next was adding one unit at a time and fiddling until it worked.

I removed the 12v+ as it is not used in the NMEA transmission. The 12v- is used by Garmin and maybe others as the NMEA return.

Good Luck, Larry

[Pblais]

[quoteWithout a multiplexer or a unit that can take listen to more than one talker, you can only a single listener can only read from one talker. One talker can talk to more than one listener so some prioritizing may be in order.[/quote]

One talker can supply 3 listeners using a simple bus bar. The standard says only three but some instruments put out a stronger signal than others. With multiple talkers and many listeners the multiplexer "serializes" the signals. It combines the many inputs into one single stream of output that now can be shared by many talkers. You can't just connect multiple NMEA outputs to a common bus and expect it to work reliable.

With multiple talkers you never know when one will talk and they can actually talk at the exact same time thus block each other.

It's not totally clear from the diagram but it appears the depth is going into the radar display to one input and the GPS to another radar input. From the rest of the diagram it appears you are just sharing the GPS output to everything else then adding a GPS Input to the GPS from the PC to upload routes. Most auto pilots will use a NMEA In too.

Were you to connect the multiple outputs to the multiplexer you could share the output with everything that listens. You don't need to worry about what sentences will be used because the ones the device can not use will be ignored. Most PC software can handle several of the different types with the same information.

Next was adding one unit at a time and fiddling until it worked.

Fiddling? What do you fiddle?

[fairbank56]

Originally Posted by Pblais

One talker can supply 3 listeners using a simple bus bar. The standard says only three but some instruments put out a stronger signal than others.

While 3 to 4 listeners is generally considered a "maximum", the standard does not say "only three". I have the NMEA 0183 version 3.00 manual here in front of me and under hardware specifications it states, "One talker and multiple listeners may be connected in parallel over an interconnecting wire. The number of listeners depends on the output capability and input drive requirements of individual devices."

Eric

[Antares]

On the multiplexer and sentences; The unneeded sentences will be ignored, but if something is looking for a specific sentence and it is not in the stream then unhappiness results. By fiddling, if it does not work initially I will test the connection to the newest device to verify the NMEA data is being received, and may also temporarily conncect it directly to the talker to see if that makes a difference. The other thing I may try is changing the talker's NMEA version.

My disclaimer is I just do this for the "fun" of it.