Generating Teletype Messages for an Ancient Machine

How did people send text to each other over great distances before email, but after telegraphs? With teletype machines, which got really popular during World War II and eventually evolved into digital communication protocols. Brian acquired a fascinating old Lorenz 15 teletype machine and wanted to use it, so he built this Arduino-based TTY generator.

Teletype machines like the Lorenz 15 are electromechanical systems. Imagine something like an electric typewriter driven by relays connected to a phone line. Without an appropriate signal on that phone line, nothing happens. In this project, Brian used an Arduino to generate that signal so the Lorenz 15 could do its typing.

Luckily, Brian had a teletype modem to start with. That is what interprets the signals on the phone line to drive the teletype machine. But trying to play recorded teletype signals directly into that modem’s receiver didn’t work.

Brian’s solution was to connect a speaker to an Arduino Mega board and place that on the modem. It generates a signal that simulates what the modem would hear over the phone line. The code to do that is fairly simple, as the timing and tones are trivial for the Arduino to produce. It outputs to the speaker placed right on the modem’s receiver and a test with a handful of “A” characters was successful.

From there, Brian was able to expand the Arduino sketch to contain the codes for all the characters. After that, it was easy for Brian to create a function that translates ASCII character codes into the teletype character codes.

Now Brian can feed the Arduino ASCII strings and it will spit out a teletype signal for the modem to send to the Lorenz 15.

Next, Brian wants to link the Lorenz up to a custom-built relay computer and the lessons learned in this project will serve him well there.