The digital pins of two Arduinos are connected for half duplex communication:
Now I want to connect the electrical connection with optical communication through a light pipe:
Drafts for separate input and output circuits (untested, I'm new to this):
How do I make combined I/O circuits for replacing the wire? (boxes with question marks)
Baud rate can be low, e.g. 100.
Communication really needs to go via just one digital pin per Arduino.
The Arduino does not have free timers left over.
Additional components are fine.
For input, the digital pin is pulled high. This is already in the existing code, which I would like to use unchanged.