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Old 25-01-2017, 18:03   #1
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Possible to use same terminals for multiple NMEA 0183 devices?

hi everyone,
I've got my depth sounder wired up to my raspberry pi via a rs422 to serial to USB converter. I am wondering can I wire multiple NMEA 0183 devices onto the same terminals that will then use the same interface to the raspberry pi. I am presuming not given that the voltage from multiple devices would not be understandable if they're reporting at the same time but figure I'd ask before I go buying more rs422 to USB dongles.

thanks in advance,
Jayson
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Old 25-01-2017, 18:35   #2
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Re: Possible to use same terminals for multiple NMEA 0183 devices?

Unfortunately, you'll need a separate rs422 to USB converter for each NMEA 0183 device. The good news is that with kplex (see stripydog.com) installed on the Pi (and possibly a USB hub if you need more ports), you can have a really powerful and flexible NMEA multiplexer.
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Old 25-01-2017, 18:53   #3
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Re: Possible to use same terminals for multiple NMEA 0183 devices?

that is precisely what I'm doing!
thanks for the prompt reply.

Jayson
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Old 25-01-2017, 23:24   #4
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Re: Possible to use same terminals for multiple NMEA 0183 devices?

Single talker, multiple listeners
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Old 26-01-2017, 11:02   #5
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Re: Possible to use same terminals for multiple NMEA 0183 devices?

Why not simply connect all the devices to a multiplexer and they connect to you device via bluetooth? I think it would work out cheaper than multipe converters and gives you wirless access.
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Old 04-02-2017, 00:07   #6
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Re: Possible to use same terminals for multiple NMEA 0183 devices?

You could use a "Merging Box" (not a Multiplexer Box) to merge datas provided by different devices.
Those datas will be transmitted on a backbone (existing or added) and displayed on different displays.
See attachment.
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Old 04-02-2017, 00:34   #7
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Re: Possible to use same terminals for multiple NMEA 0183 devices?

Quote:
Originally Posted by roland stockham View Post
Why not simply connect all the devices to a multiplexer and they connect to you device via bluetooth? I think it would work out cheaper than multipe converters and gives you wirless access.
That's exactly what a Raspberry Pi running openplotter does. Very well and cheap. Serial/USB converters don't cost much.
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Old 04-02-2017, 01:05   #8
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Re: Possible to use same terminals for multiple NMEA 0183 devices?

Quote:
Originally Posted by gmartin83 View Post
You could use a "Merging Box" (not a Multiplexer Box) to merge datas provided by different devices.
Those datas will be transmitted on a backbone (existing or added) and displayed on different displays.
See attachment.
A 'merging box' is just a non technical name for a multiplexer.
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Old 04-02-2017, 13:30   #9
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Re: Possible to use same terminals for multiple NMEA 0183 devices?

Merging and multiplexing are two different operations, there is an enormous difference.

Here is a multiplexer:

Name:   multiplexer.png
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Old 04-02-2017, 16:39   #10
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Re: Possible to use same terminals for multiple NMEA 0183 devices?

If all you are doing is merging on a 183 network then you are back to a single talker, multiple listeners. Which is what you get when you wire the devices together, ie wire-or. Or does this merger do something similar to a multiplexer,?
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Old 04-02-2017, 17:47   #11
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Re: Possible to use same terminals for multiple NMEA 0183 devices?

As others say: one input line one talker only. N183 limitation. The problem comes from the serial talkers being dumb and not negotiating the bandwidth access. You can get many talkers in at once only if they use a talking protocol that allows for listening prior to talking. Is this NOT so very human??? ;-) ;-)

Or else you can multiplex the signals up first and then use a single input line. You can build your own multiplexer from an old router, some USB/serial wholesale chips, and a usb hub. I think about 5 bucks per each channel.

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Old 04-02-2017, 18:44   #12
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Re: Possible to use same terminals for multiple NMEA 0183 devices?

Quote:
Originally Posted by gmartin83 View Post
Merging and multiplexing are two different operations, there is an enormous difference.

Here is a multiplexer:
Attachment 140693
So what exactly does a merger do?

Perhaps if that diagram was labeled with TXa, TXb, RXa, and RXb it would be clearer. As drawn I can't tell how it wires up, so can't begin to guess what it does.
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Old 04-02-2017, 23:22   #13
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Re: Possible to use same terminals for multiple NMEA 0183 devices?

Hello,

Let's see an exemple, B&G network.

Several units add or merge phrases onto the backbone, example :
Wind unit add $IIVWR Apparent Wind angle and speed
Speed unit add $IIVHW Speed
Of course, doing that, the units must avoid collisions on the backbone (merging process).
Now, the "merging box" does the same job, but it merges your own data.

Other units, for example Autopilot or your Arduino unit, will "read" theses phrases.






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Old 04-02-2017, 23:44   #14
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Re: Possible to use same terminals for multiple NMEA 0183 devices?

Quote:
Originally Posted by gmartin83 View Post
Hello,

Let's see an exemple, B&G network.

Several units add or merge phrases onto the backbone, example :
Wind unit add $IIVWR Apparent Wind angle and speed
Speed unit add $IIVHW Speed
Of course, doing that, the units must avoid collisions on the backbone (merging process).
Now, the "merging box" does the same job, but it merges your own data.

Other units, for example Autopilot or your Arduino unit, will "read" theses phrases.
I think you are talking about NMEA 2000? And a NMEA 0183 to NMEA 2000 converter?
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Old 05-02-2017, 00:30   #15
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Re: Possible to use same terminals for multiple NMEA 0183 devices?

No, notice I mentionned NMEA0183 phrases, not NMEA200 pgn.
See B&G network, please.
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