I am not sure if the resistance at the input of the optocoupler is only for the indicator LED or also for the optocoupler itself. In either case I used a 10k resistor but I also tested it with a 4k7 resistor.
I discovered it by chance when I was handling the cables and a false contact allowed me to see seatalk data for a moment.Then I thought the optocoupler input was saturated.
Now it is not easy for me to look because I made the assembly in black box mode and placed it behind the bulkhead of the electronics and connections.
In any case this circuit is not only more solid than the other with the set of 4 optocouplers. Also its connectors are better and easier to use. And since the other circuit also has to add the resistance to the output I got this one I like best.
Edit to ADD:
I found the photo of the circuit below and so it seems that the LED diode is in series with the + and the resistance in series with ground.
![[Image: HTB1nGzIMVXXXXaiaXXXq6xXFXXXG.jpg]](https://ae01.alicdn.com/kf/HTB1nGzIMVXXXXaiaXXXq6xXFXXXG/224361831/HTB1nGzIMVXXXXaiaXXXq6xXFXXXG.jpg)
So it seems that if you can replace the resistance directly even if I mount it like this:
![[Image: f3Q0bax.png]](https://i.imgur.com/f3Q0bax.png)
I discovered it by chance when I was handling the cables and a false contact allowed me to see seatalk data for a moment.Then I thought the optocoupler input was saturated.
Now it is not easy for me to look because I made the assembly in black box mode and placed it behind the bulkhead of the electronics and connections.
In any case this circuit is not only more solid than the other with the set of 4 optocouplers. Also its connectors are better and easier to use. And since the other circuit also has to add the resistance to the output I got this one I like best.
Edit to ADD:
I found the photo of the circuit below and so it seems that the LED diode is in series with the + and the resistance in series with ground.
So it seems that if you can replace the resistance directly even if I mount it like this: