NMEA

[christopherc]

I'm sure this must be straightforward; my gps talks to the DSC radio, but not the radar or autopilot, both capable. As the gps has only one NMEA output, do i need some kind of junction box to get them all talking to eachother? Not essential, but if they can do they might as well do.

 

[bdsweeting]

The GPS might only be able to feed a couple of other units I understand.

You could try it and see what happens; if it fails then you will need a NMEA multplexer box which will take an input and feed it out again but with a stronger signal.

 

[bobgosling]

You may need a buffer ( see here )

Alternatively, some VHFs accept a NMEA signal in for the DSC info then pass it back out agin. Check whether your VHF has an NMEA out signal.

Usually it should be OK to add up to 4 receivers to one sender so also check your connections

 

[christopherc]

Thanks, I've read that 1 nmea device should drive 3 or 4 outputs, but can't find out how to make the connections, can i for instance buy a cable with one input, four ouputs? I'll check out the backof the radio. The radar has just one NMEA input, so I guess I have to split the signal somehow. Multiplexer seems to be for when I have more than one NMEA device wanting to send information, which isn't the case here, I just want the one device, gps, to send to three others

 

[Richard10002]

I feed mine into one of those plastic connector block things with screws, then take 3 or 4 outputs from the other side.

 

[christopherc]

.... and that works? sounds ideal, for some reason i was expecting a more technical solution

 

[Guest]

A normal NMEA signal ex GPS is capable of up to 4 items to be fed. In fact often this can be exceeded .... some instnces of 5 or 6 items connected.
The more items - then the more important the length of cable and shielding becomes important.

Multiplexer - this is an item that is often quoted - but is in fact for a different job. Some NMEA items are talkers and listeners - so it is bad practice to just link more than one talker - so a Multiplexer is used to seperate and control talkers - It is NOT a multiple junction only.

To connect your radio / radar / DSC etc. - plain splitter box is all you need .... in true Blue Peter style here is one I made earlier : >

Here connected between PDA and GPS .... another 2 items can be connected (1 being a PC) .... here is item on its own : >

It is made from a household electrical junction box ... and serial mouse leads / serial plugs / sockets ...... available at maplins etc.

I also created another splitter with a telephone socket and cable .... : >

With the telephone socket - you can actually increase items by use of telephone doubler plugs !! Crazy but true.

The real limitation comes when you have a USB connection GPS ... as then you cannot use a USB hub to split signal - there is some blocking inside and the hub will only split the PC side out .... other sockets do not talk to each other ... tried it !! So here you need a specialised USB splitter or easiest way is to connect to PC and then use PC to supply passthrough to a USB hub.

If your GPS is supplying nmea via a bare end cable or serial plug (RS232) - then thats the easiest and best way ....

Honestly - there's no real work to this and it is easy once you get the hang of it ....

 

[philip_stevens]

What model of GPS do you have?

My Navman 5500 would not talk to my Furuno radar (of a different era), but the older AP-Philips Mk6 does. It may be that the GPS is sending a slightly different make-up of NMEA to that of the older AP.

The radar info stated that it would receive Loran input, so that dates the radar to the same age as the AP. Maybe same language but different accent /forums/images/graemlins/confused.gif

Not even 2 GPS's, but 3! as the 3rd (AP-Philips Mk8) is in the cockpit in place of the duff log display. The cabin log is from the Navman 4380 fishfinder. One day I may fit a remote NMEA display in the cockpit for the log.

 

[Seastar]

Ecellent solution!
I find that if the signal starts to degrade due to load then, baring home brew solutions, it is cheaper to buy another GPS. I have one which drives the DSC data and second with drives the plotter/authhelm/PDA. It aslo an easy solution for sytems that require bi directional data.

 

[Richard10002]

[ QUOTE ]
.... and that works? sounds ideal, for some reason i was expecting a more technical solution

[/ QUOTE ]

Works fine for me

 

[duncan]

once you have them physically connected up you need to ensure tehey are speaking the same language - so to speak - as phillip s alludes

NMEA 0183 versions have slightly different sentences and I have found that whilst many later devices are able to handle a range (1.5 and 2.0 for example) some are not - my JRC Mk1 1500 radar for example

you will need to check the device manuals to find one they can agree on! then set the GPS to send that one and the others should be happy!

 

[LadyInBed]

I have my very old Magellan Meridian 4 ch GPS connected to the JRC Radar, Autohelm and laptop.

I ran about 20 to 25 feet of external telephone cable and doubled up the wires to help reduce losses.

The devices (listeners) are all wired in parallel (device + to + to + and - to - to - ).

I then changed the GPS (talker) NMEA output trying 1.5 & 2 till I got a response on all listeners.

It has all worked fine now for 5 years.

Another thing to add into the circuit, like SBC has done, is a box with a DB 9-Pin (RS232) plug. Then if your fixed GPS goes down, you can plug in a hand held GPS and restore input to all the listeners.

 

[Guest]

Re: NMEA ..... seems LadyInBed and I agree !!

It really is simple .... I use tel- cable for long runs as it comes in multi-core, in flat or round, is easily soldered / worked. For short connectors - get an old Serial mouse and cut of the cable - ready made serial cable .... just Identify the leads to which pin ...

I reckon a box with a RS232 socket on each side ... then you can connect whatever you want ... mine has provision for 3 out sockets ... 1 in ..... sockets available ex Maplins about a quid each ...

My set-up currently caters for any combinbation of :

Magellan Meridien 8ch GPS
eTrex 12ch GPS
Lowrance 3500C GPS plotter
Notebook PC ( via usb-serial prolific cable)
Notebook PC via RS232
HP Jornada PDA

I can also supply extra feed to other items via PC passthrough ...

If I can help - then PM me ...

 

[bobgosling]

[ QUOTE ]
Multiplexer - this is an item that is often quoted - but is in fact for a different job. Some NMEA items are talkers and listeners - so it is bad practice to just link more than one talker - so a Multiplexer is used to seperate and control talkers - It is NOT a multiple junction only.


[/ QUOTE ]

If you scroll down past the Multiplexers in my link ( web page ) you will see items listed as Buffers. These are effectively doing the same thing as an Aerial Booster and amlifying the signal to allow more loads ( readers ) to be connected.

 

[Guest]

Bob ... scroll up before YOUR post ....

That is who I was posting about M/plexers .... Christopher mentioned MP's without other reference. An item I wished to correct.

Whether your post had buffers etc. - not a problem as it was not your post I was referring to.

As many know and others have also confirmed in the many threads on this very subject - splitters of NMEA signal are simple wire to wire connections ........... and there are 2 very simple ways to increase ebven further NMEA sourcing .... a) buy a cheap e-bay GPS unit ..... providing back-up in event of main failure .... b) passthrough from Notebook PC.