Alternative SeaTalk wiring

[Sailoog]

Thanks for reporting Duncan.

Please try the new wiring.

You can also try the old wiring but adding a 4.7K or 5K resistor in serial with the MacArthur Seatalk1 DATA connector. That will give us more clues.

[Boatingbaileys]

Ok, I’m back at the boat and with the new wiring, inverted, and jumper set to ST and/or removed I only see navigation.log and navigation.trip. I then waited about two mins and headingMagnetic and rudder.angle appeared. After some more time gnss appeared with a null value. I’ll wait a little longer to see if I get more fields but it seems very slow and is if there is too much resistance/low signal strength.

Anything else I can do to test this for you?

[Adrian]

Can you remind me whether the original Seatalk wiring worked with your setup or not?

---

If you have a volt meter, can you check whether the ST Data line idles at 12V?

[Boatingbaileys]

Can you remind me whether the original Seatalk wiring worked with your setup or not?

---

If you have a volt meter, can you check whether the ST Data line idles at 12V?

Mine works correctly with the old wiring and has done with the HAT and the Octo I used before. It does not idle at 12v. The highest I’ve seen on the multimeter is 6v but it’s bouncing from 0 to about 5.

[Adrian]

So much for my theory. If Seatalk data idles at less than 12V its surprising that you get any data at all with the alternative wiring.

Caveat, measuring with a multimeter is problematic as it will average voltage levels if there's active traffic. I recently came across this site, which also says that data idles at 12V: http://www.thomasknauf.de/seatalk.htm

Two alternative explanations:

1. The signal on the Raspberry Pi side of the optocoupler isn't "digital" enough to be properly decoded
   
2. The Pi drops bits as it can't read the GPIO consistently enough to decode at 4800 baud - though not clear why that wouldn't be an issue with the original wiring
   

I think I will have to get my hands on a Seatalk1 system to debug this issue.