This great video explainer shows the inner workings of a digital-to-analogue converter, using the IBM Selectric's early example of the form to illustrate the mechanism:
Using slow motion video Bill Hammack, the engineer guy, shows how IBM's revolutionary "golf ball" typewriter works. He describes the marvelous completely mechanical digital-to-analogue converter that translates the discrete impulse of the keys to the rotation of the type element.
IBM Selectric Typewriter & its digital to analogue converter (Thanks, Fipi Lele!)
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.