[Aris]’s thru box design uses an optocoupler on the input, which connected to 74HC14 hex inverting Schmitt trigger. The schematic shows three outputs, but there’s room for adding two more.

Vishay has introduced a series of 1Mbaud (2MHz NRZ) optocouplers with built-in Schmitt trigger and open collector output. Called the VOH1016A series, the typical input current for output turn-on is ...