NMEA 0183 or SeaTalk-1 -> RPi4


Trying to understand how I can interface with NMEA 0183 and/or SeaTalk to read instrument data from a sailing boat.

Course Computer is Raymarine Autohelm 100/300

From what I can see it looks like there are 2 options:

  1. NMEA output from the Course Computer: Would require an RS-422/485 Hat to sit ontop of the RPi4

  2. SeaTalk cable that I can use an Optocoupler to transform the 12v down to 5v then connect that directly to the GPIO pins on the RPi4 e.g. here: Connect Seatalk-1 devices to Openplotter using GPIO - YouTube.

Am I correct in my understanding or is there a cheaper/easier route?

Thanks in advance!


Hi Kevin,

From the looks of things, Seatalk is going to be cheaper and easier to get working. Looks to be a 1-wire communication bus. An optocoupler is a great idea in either case, an RS485 HAT will likely use one anyway.

Are there any trade-offs data-wise for choosing one or the other?

Here are two options from our store to give you an idea on price:

Keen to hear your thoughts!

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Hi Kevin (and James)

I would go with the NMEA model as that is a very well defined protocol and quite straight forward to disassemble for display.

FYI I am considering using it ( or a reasonable subset ) between a remote weather station head and the display system.

Also this module is available


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Thanks very much for your input, guys!

Looking at the manual it seems that the SeaTalk network exposes additional data that isn’t available on the NMEA outputs.

If I went down the Optoisolator route I would still need the resistor from the 12v wire before connecting to the optoisolator right?

Sorry for my newbie-ness as I’m just learning electronics, but I have been developing web-based software for decades so once I can read the data then the rest will be easy.

Thanks again!

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