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Old 12-03-2015, 17:22   #1
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NMEA 0183 isolator/buffer

The NMEA output from my venerable Navman plotter gets a bit overloaded and gives up when I plug the serial-to-usb converter in (to feed OpenCPN on the laptop). Feeding the tillerpilot and VHF is ok, but the serial-usb seems to be a bridge too far.

The serial-usb converter is an ebay el-cheapo. Can anyone recommend one that provides isolation/buffering so as to not drag the NMEA bus down?

Cheers, Graeme
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Old 13-03-2015, 08:06   #2
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Re: NMEA 0183 isolator/buffer

Actisense - Home - Manufacturers of Marine Electronics


They make great stuff at great prices.


One small point, however -- no buffering problem by a "listener" will interfere with the "talker", or other listeners, it will just corrupt the data on that listener. What you've got sounds like an electrical problem.

I would start with the Actisense USG-1 and see if that solves the problem.
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Old 13-03-2015, 08:11   #3
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Re: NMEA 0183 isolator/buffer

You might need a multiplexer. Practical-Sailor featured one a while ago:

Multiplexing Marine Electronics - Practical Sailor Print Edition Article

You can Google "NMEA 0183 multiplexer" for other options.
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Old 13-03-2015, 08:59   #4
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Re: NMEA 0183 isolator/buffer

The NMEA 0183 physical layer is based on EIA-422. Is your serial converter an RS-232 to USB converter? NMEA devices can sometimes drive a single RS-232 connection (even though it isn't really in the physical layer standard) but if you have existing true NMEA 0183 devices on the circuit then you would need an RS-422/485 to USB adapter.

If that is what you already have then it could be an electrical problem with the comms circuit (probably a grounding issue with the new device). You could put in any RS-422/485 isolator/repeater to test out that concern. Actisense (as linked above) has them, or you can get non-marine industrial control versions generally for less money (and some of them are conformal coated and so really no problem with the marine environment).
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