Ins and Outs of NMEA

[dmayes]

As far as I am aware NMEA out will drive more than one device so you can connect say a GPS unit to both a tiller pilot NMEA in port and a DSC radio NMEA in port. Both should work and in theory you could possibly connect the GPS with up to 6 devices. However, you cannot connect two NMEA talkers together. So If I had an NMEA wind transducer I could not connect it to the previous tiller pilot as it would interfere with the existing GPS connection. Does anyone make a device that can receive the NMEA data from say a GPS, plus a digital compass and also a wind transducer, then combine all the sentences and output them in one go to all instruments that would benefit?

 

[alan]

What you need is a multiplexer. You should check the data rates of the devices that you need to multiplex to ensure the multiplexer will handle those data rates (e.g. AIS devices use higher rates than others).
Multiplexers can be obtained from a few sources but the best prices that I have seen are from JG Tech
Go their "Web Shop" page and you'll see a choice of multiplexers listed there.

Alan.

 

[bedouin]

Not quite what you asked - but I have put a simple switch into the feed to the autohelm so that I can have either wind or gps data going in but not both at the same time.

 

[Jonny_H]

Try these guys:

www.shipmodul.com

They have a useful section on talkers and listeners and how to connect multiples of each (click NMEA Info on left hand panel).

I emailed them with a query and they very helpfully replied telling me how to solve my problem without spending a penny! (Very honest)

Jonny

 

[Graham_Wright]

I was told (from somebody at MES I think) that you can connect two (or indeed more) talkers together. Open collector drivers will avoid any electrical burn-ups. As a onetime digital engineer, I found it hard to believe tha the data could be decipherable. Having worked on several serial transmission systems (and invented one!) it seemed to me that there had to be some cooperation between talkers to avoid conflicts. The answer I ws given to this was, that if they all talk at different intervals, eventually a decipherable sentence will escape which can be decoded by a listener. I suppose this could work if the data is required at a low rate but it still seems unlikely.

Mulitplexing is the answer;- just add money!

 

[simonfraser]

my nmea wind out goes into the plotter then out of plotter into autohelm - does that help ?

 

[dmayes]

Thanks. both multiplexor sites are good, I did think about the switch. A normal double pole double throw switch would do but you have to remeber to throw it when you change and it would only solve the immediate problem with the tiller pilot.

 

[bobgosling]

[ QUOTE ]
Thanks. both multiplexor sites are good, I did think about the switch. A normal double pole double throw switch would do but you have to remeber to throw it when you change and it would only solve the immediate problem with the tiller pilot.

[/ QUOTE ]

Make it a DPDT switch and combine it with the autopilot on/off ?