The digital pins of two Arduinos are connected for half duplex communication:

Electrical connection

Now I want to connect the electrical connection with optical communication through a light pipe:

Optical connection

Drafts for separate input and output circuits (untested, I'm new to this):

Drafts for separate circuits

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.

  • \$\begingroup\$ <strike>Have you considered looking into IrDA transceiver modules?</strike> Never mind, I missed the half-duplex part. \$\endgroup\$ – Hearth Oct 7 '19 at 13:38

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