When I was a kid, my dad connected a Model 19 teletype to our Apple II computer for amateur radio teletype (RTTY). He used an opto-isolator to protect the Apple

When I was a kid, my dad connected a Model 19 teletype to our Apple II computer for amateur radio teletype (RTTY). He used an opto-isolator to protect the Apple II from the 60 ma loop that the Model 19 used.