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!)