Do I need a multiplexer?

[dukes4monny]

I am looking to include an NMEA depth input to my Navman 5500 plotter, but I also want to add a DSC radio which needs an NMEA output from the plotter..........
The yacht came with the Navman plotter already fitted, it's fitted into the cockpit coamings which makes it difficult to access the wiring.
Being a complete electronics novice, I thought I would seek the advice of the wise sages of this forum before I start unraveling the spaghetti of wires that I'm sure to find:
How do I go about achieving the above tasks?
Can I simply wire the separate NMEA devices into the back of the plotter......or
Do I create a 'junction box' with one lot of wiring from the back of the plotter and seperate inputs / outputs for the radio / depth........or
Do I have to get a multiplexer to be able to interface more than one NMEA device?
If it's a straightforward job I'd like to do it now.........but if it's going to be a fiddly job I'll leave it until haul-out time.

Thanks for help.

 

[nimbusgb]

NMEA depth will go into the plotter, NMEA data out does to the DSC. Pretty much like a dual carriageway. Traffic can go both ways simultaneously

No reason to get complicated, it should be a doddle.

Ian

 

[alan]

Probably not. However, if you only have one NMEA port on the plotter, you should check that the depth sender and the radio both work at the same speeds (bauds or bits/sec); it is unlikely that you will be able to set the transmit and receive side of the NMEA port to different speeds. (Maybe the Navman has more than one NMEA port ??)

Alan.

 

[dukes4monny]

Ok thanks, I was hoping it was going to be easy........that's the way I like things /forums/images/graemlins/smirk.gif
I forgot to mention in my previous post that the plotter already has an NMEA output wired in for the tillerpilot.
I have left the manual on the boat, but from what I can remember, the plotter has an NMEA + and an NMEA - .......are you saying that everything can be wired to these two and they'll all happily talk to each other?

 

[nimbusgb]

NMEA standard says you can multidrop devices. Some manufacturers interpretation of the NMEA standard is a little dodgy. You cant do any damage by trying it.

 

[alan]

You need to wire the depth transducer to the NMEA IN "+" and "-"; then you need to wire the tiller pilot and the radio (in parallel) to the NMEA OUT "+" and "-". You should be able to drive at least those two devices on the output without any problems. You may need to enable the correct sentences on the output port for the radio (probably GLL) if it is not already enabled (you can find instructions in the Set-Up part of the manual).

Alan.

 

[dukes4monny]

Managed to download the plotter manual (thank you Google), this says I have three wires concerning NMEA:
Black Ground (power negative, NMEA)
White NMEA out, to autopilot / radar
Blue Navbus or NMEA2 input

I have an NMEA + and an NMEA - for my depth info, so do I: connect my (depth) NMEA + to my (plotter) NMEA2 input
connect my (depth) NMEA - to my (plotter) Ground?

Sorry, I know this is probably basic stuff, but I don't want to end up frying anything.

Thanks again for your advice.....I love this forum /forums/images/graemlins/smile.gif

 

[alan]

Yes.

 

[dukes4monny]

Thanks Alan, as I have only three wires, does this mean that I use the same "-" for both the input and output connections?

 

[dukes4monny]

you are quicker than me /forums/images/graemlins/laugh.gif thanks.

 

[nimbusgb]

yes - is common to both depth an dsc radio

 

[bobgosling]

A lot of manufacturers use the boat 12v negative line as "NMEA -" so you can usually consider them as interchangeable. You should be able to drive about 4 NMEA readers with relative ease. Make sure you have good connections and don't skimp on wire thickness to minimise voltage drops.

 

[dukes4monny]

Thanks to all for your helpful replies. I can now tinker with confidence /forums/images/graemlins/cool.gif

 

[moody1]

Multiplexor is definitely not needed. It is purely a unit to stop multiple talkers from talking at same time and basically having nothing.
Simple wiring is all that's needed, no fancy boxes at all. Many people use simple screw terminal blocks.
Depth is connected to NMEA in to plotter, radio is connected to NMEA out from plotter.