Here is the schematic for my old digi interface. It is very basic interface with two RX lines. I made the printed circuit board years ago but was never drawn the schematic for it. Some people had asked it so there it is. It may not match perfectly with the board layout but the idea is the same.
I am going to design a new version with some improvements later. All suggestions for the new version are welcome. I will share the circuit and the board layout so you can build it too.
As you can see there is nothing new in this circuit. The same circuit has been published many times before. My whole point was to make the nice board for it. I added two RX lines for radios like FT-1000MP etc.