Arduino speaks teletype to an old Lorenz 15

Brian got his hands on an old Lorenz 15 teletype machine, which was made in the 1950s. He also managed to snag an appropriate teletype modem. But the modem couldn’t seem to understand recorded teletype messages, so Brian used an Arduino Mega 2560 to “speak” teletype and get the Lorenz 15 printing.

You can think of the Lorenz 15 with teletype modem as a bit like a vintage terminal with an acoustic coupler modem. The modem listens for an encoded sequences of tones via a telephone handset, then tells the electromechanical Lorenz 15 which keys to actuate. In theory, one can record the audio played through the handset and then play that recording into the modem. Sadly, that didn’t work for Brian and the modem just didn’t understand what it was hearing — probably because the recording wasn’t perfect.

Brian’s solution was to program the Arduino to play the proper tones with the proper timing to transmit teletype characters. The board plays that through a small speaker placed on the modem where the telephone handset would normally go.

He started with the basics and transmitted the “A” character a handful of times. After confirming that worked, he expanded the Arduino sketch to cover the whole character set. And finally, he created a function to translate ASCII character strings into corresponding teletype messages.

Now Brian can transmit any message he likes through the Arduino and the Lorenz 15 will dutifully print it out.