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Transmitting on Seatalk?
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2025-10-24, 04:33 AM
Does anybody have a solution for transmitting on Seatalk? The only instrument that I need to talk to is my Raymarine ST1000. I'm hoping that someone else has created an adapter that will transmit. The way I figure it, it can use the existing Seatalk I/O pin in conjunction with other "enable" pin to actually drive the bus with the signal. It wouldn't need much, just one transistor and a few passives.
Transmitting Seatalk is non-trivial, as the protocol is bi-directional and needs to gracefully handle collisions. The MacArthur HAT does not have the hardware to do that, and you'd probably need some additional components to safely implement that via I/O pins.
There are several older threads on this topic in this forum, for example: https://forum.openmarine.net/showthread.php?tid=5059
2025-10-26, 11:10 PM
(2025-10-26, 08:25 PM)Adrian Wrote: Transmitting Seatalk is non-trivial, as the protocol is bi-directional and needs to gracefully handle collisions. The MacArthur HAT does not have the hardware to do that, and you'd probably need some additional components to safely implement that via I/O pins. Yes, I know it doesn't have the hardware, but such hardware is not much more than level shifting and an enable control to drive the bus. So two more I/O pins would be involved, one to enable driving the bus, and another one to drive the data onto the bus. You couldn't re-use the input pin for an output pin because you would have to be reading the input pin to make sure that you are receiving what you are sending, to detect collisions. Maybe create an external board using a RPi Pico to read the ST1 and do the needful to write to the ST1. Have it talk to the MacArthur using I2C, so no changes needed to the MacArthur. Just have to add an I2C driver to read the ST1 from the RPi Pico. I see at least two people who need such a thing, and maybe a dozen more who have an interest but haven't expressed it. |
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