[sje]

Nearly all of the older TeleType (brand name) machines along with their clones used a serial 20 mA current loop interface and Baudot (5 bit) (later ASCII 8 bit) coding. It was quite common in the Old Days for micro hobbyists to interface with these; a serial I/O port and a converter circuit was used. A little research is needed to determine details of the 20 mA conversion, as I've forgotten.

The Baudot code worked by having two character sets, Letters and Numbers. Each had thirty codes along with a Letter Shift and a Number Shift code. These latter two codes would put the receiver into Letter or Number mode respectively. And that's why you've never seen lower case letters in a Western Union Telegram. It's not a good idea to use Baudot code for programming, as you can guess.

Later Teletypes had an ASCII option, the long remembered KSR-33 and ASR-33 models were examples and were commonly seen in the Old Days. These 10 CPS units were later supplanted by better models that could support both upper and lower case characters and higher speeds; I remember a 30 CPS unit dating from the late 1970s.

Locating ink ribbons and perhaps paper for any of these could be a problem. Also, they are rather noisy in operation and earlier models were prone to mechanical failure.