Seatalk voltages

MattiR

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Thanks for the input Laika. Indeed there's a lot learn, can't say I know too much about signalling. For the collisions I'm not worried, because everything else is doing n2k. For the moment things around here are more or less at halt, so I'll keep on digging. But as soon as we get some sun and higher temperatures, I'll be off working on the boat, so no clue if I am able to finish this any time soon.
 

MattiR

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Thanks, I see. I was thinking about this, but erraneously from a setup with two wires, one for tx, one for rx. SO, if raspi talks and plotter talks, there is a situation that needs to be solved. Thanks for this.
 

laika

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Thanks, I see. I was thinking about this, but erraneously from a setup with two wires, one for tx, one for rx. SO, if raspi talks and plotter talks, there is a situation that needs to be solved.

Exactly that: NMEA0183 has only one device controlling a Tx line so no collision avoidance required. Seatalk is bus-oriented. Everything shares the same three wires. The mechanism seatalk uses to try to limit confusion is described on the site AngusMcDoon referenced earlier:
Thomas Knauf SeaTalk Technical Reference

In the past I've said "oh...you can't really do bus collision avoidance like this well from user space on Linux" but that was back when the pi was single-cored and I was being to prissy about a very slow protocol. I'd probably want to reserve a core and run my program real-time, bit banging through gpio rather than using the uart but hey, 4.8k vs modern processor? A naive implementation would probably be fine. (opinions?).

I don't know what your systems programming skills are, but this is probably not a beginner level programming project.

Of course if there's only one talker in your project it doesn't matter.

If you do in fact have a ST60 multi which will accept NMEA0183, stick to that :).

If it is the ST60 wind and you do need seatalk, offloading to a microprocessor is without doubt your best bet. Again beware of random arduino code on the Interweb which may not implement collision avoidance. NMEA0183 to Seatalk interfaces seem to retail at about £100. AngusMcDoon's YAPP was a fraction of that...Are the schematics/code still available?
 

MattiR

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Thanks. I did'nt think far enough when starting to fiddle with this. Right now I only have tho devices, raspi is the talker and repeater ST60 obvilously only listens.
As for my proramming skills, I've done moderate level c coding, and usually get it done. But that has been only coding. Signalling is new territory.
One solution popped up while taking a hike in the forest. Maybe translating nme0183 to nmea2000 and pass it via can bus to the plotter, then have only plotter talking to nmea0183 net. I already have the can bus up. But then again, if the display does not support nmea, this doesn't work. I might revive experimenting with boosted pwm output.

Thomas Knauf SeaTalk Technical Reference is still intact
 

MattiR

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Thanks for everyone. Appeared unnecessary worksome to try to stick to just the raspi, so I eventually ended up with passing nmea to arduino uno, which I set up to put out seatalk messages through a tiny signal booster to the st60 wind display, my only seatalk1 device. Seems to work okay.
 
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