Re: Another elevator anecdote.
My days were mid 80s onwards. Yes you'd use RS422 or current loop in olden times.
I actually did build and maintain a few 20mA current loop setups when playing with RTTY as a spotty youth - mainly to tame the prodigious EMF kickbacks you get out of old style Creed model 7 teletype.
I did a bit more with loops and optoisolators in later years interfacing various ancient technology in university laboratories to "modern" computers
Biting the hand that feeds IT
