How does a teleprinter work?
The original teletypes were electromechanical devices. Fairly simple electrically, but moderately complex mechanically.

To transmit, each key on the keyboard changes the position of five levers or bars in a particular pattern (32 combinations). These bars change the position of five electrical contacts, which are then "scanned" by a set of cams on a rotating shaft, in order to create a pattern of open/closed circuit conditions on the electrical interface, which is a "current loop". The first bit is always an "open", and this functions as the "start" bit. The five data bits follow this in sequence.

The on/off current pulses are fed to an electromagnet on the receiving side, which operates a lever. In the "idle" state, the lever holds a rotating shaft still against the force from a motor/clutch combination. When the start bit comes through, it releases the shaft, which makes one rotation at the same speed as the one in the transmitter. During this rotation, a set of cams and linkages is used to "test" the position of the electromagnet lever during each of the data bits, and a bar or lever for each bit is set accordingly. At the end of the cycle, the combined position of the five bars enables just one of the typewriter print bars to be activated and print on the paper.