How Does Teletype Model 19 (and Model 15) Demonstration Work?

A teletype machine is like a super-duper fast typewriter that talks to another machine over a wire using simple clicks and blips.

Imagine two kids sitting in different rooms, each with a box full of colored balls. When one kid wants to say "Hello," they don't shout. Instead, they pick up a red ball (representing the letter H) and send it down a tube to the other room. The second kid catches the ball, looks at its color, and prints that letter on their paper. This is how electromagnetic relays work in Model 19 and 15 teletypes.

Inside the machine, there are five tiny metal switches stacked like a sandwich. Each switch can be either ON or OFF. Think of them like five light switches on your wall. If all five are OFF, it means zero. If only the top one is ON, that’s also a specific number. By mixing which ones are up and down, the machine creates 32 different combinations (like binary code). Each unique combination stands for a letter or symbol, such as A, B, or Shift. When electricity flows through these switches, it triggers a hammer to hit a typebar, printing your message on a rolling piece of paper tape.

The Model 19 demonstration often shows two machines talking at once. One machine is the sender, and the other is the receiver. They sync up perfectly. When you press a key on the Model 19, it instantly flips those five electrical switches into the right pattern. This creates little pulses of electricity that travel down the wire like tiny messengers. The receiving machine reads these pulses and updates its own set of switches to match. Once the patterns line up, the receiver knows exactly which letter is coming next. It’s not magic; it’s just coordinated mechanical teamwork, turning electrical clicks into written words on paper.