Dragging Teletypes Into The 21st Century

If you are of a certain age you may have worked in an office in the days before the computer revolution, and the chances are that in the corner of your office there would have been a teletype machine. Like a very chunky typewriter with a phone attached, this was an electromechanical serial terminal and modem, and machines like it would have formedĀ the backbone of international commerce in the days before fax, and then email.

Teletypes may have disappeared from the world of trade, but there are a surprising number still in private hands. Enthusiasts collect and restore them, and radio amateurs still use digital modes based on their output. The problem facing today’s teletype owner though is that they are becoming increasingly difficult to interface to a modern computer. The serial port, itself an interface with its early history in the electromechanical world, is now an increasingly rare sight.

[Eric] has a project which addresses the teletype owner’s interfacing woes, he’s created a board with all the necessary level shifters and an Atmega32u2 microcontroller to translate the teletype’s output to USB.

In his design he’s had to solve a few problems related to such an aged interface. Teletypes have a serial output, but it’s not the TTL or RS232 we may be used to. Instead it’s a high-voltage current loop designed to operate electromagnets, so his board has to incorporate an optocoupler to safely isolate the delicate computer circuitry. And once he had the teletype’s output at a safe level he then had to translate its content, teletypes speak 5-bit ITA2 code rather than our slightly newer 7-bit ASCII.

The result though is a successful interface between teletype and computer. The former sees another teletype, while the latter sees a serial terminal. If you have a teletype and wish to try it for yourself, he’s released the source code in a GitHub repository.

Teletypes have featured a few times here at Hackaday over the years. We’ve had one as an SMS client, another that monitors a Twitter feed, and while it’s not strictly a teletype, a close examination of an Olivetti mechanical serial terminal.

36 thoughts on “Dragging Teletypes Into The 21st Century

          1. Well actually that would be interesting to try! Solar LED lamp with an EPROM as the sensor might be possible.
            Thanks for the obscure idea!

  1. A lot of us used a few discrete components and an optoisolator to convert bit banged BAUDOT output to a current loop to drive a teletype such as the Model 15 I had attached to my Kim-1 in 1976.

    To prevent being evicted from our apartment, my teletype machine stood on a 30cm thick foam pad to reduce the noise and vibration.

    I miss the smell of hot machine oil when the printer was running. The noise I can do without.

  2. My first interaction with a computer was via one of these in high school in 1967 connected to Dartmouth time share. The business-only travel agency my wife worked for had a TELEX terminal until the mid eighties.

  3. Got one in the 80’s that had storage: A punch paper roll on the side of it that could record, copy and store letterhead templates. Contemplated to turn it into a loud 7 bit printer before throwing it out.

    1. Thanks for triggering an old memory.

      In 1973, I had one teletype connected to McGill University’s computer in Montreal over a phone line, and another connected to the McMaster University computer in Hamilton. The teletype terminals were in opposite corners of an office. To transfer a huge (probably a few hundred kB) amount of data from one computer to the other, I had one terminal punching a paper tape and when the tail was long enough, I fed it into a reader on the terminal on the other side of the room. Then I spent the entire night watching the tape spool across the room transferring the data. I can’t remember how many spools I went through. There was no direct way to connect the 2 computers at that time.

      When it was all transferred, I had the data punched onto cards for local storage.

      The good ol’ days.

        1. He said Mcgill. Sir George was a separate university (now known as Concordia University, having merged with Loyola in the mid-seventies. Sir George was where the “computer riot” was in 1969.

          1973 was right on the cusp, there was an article but I don’t know the year, in ham magazine around then using logic ICs to convert serial to parallel and back, so you could do tricks like watch for specific characters, but could regenerate a TTY signal to move one line to the next without going though a paper punch and then reader.

          Change can come fast, one minute no good solution, the next a much easier solution. Only decades later do the two seem to be concurrent .


  4. Talking of the 21st century, I saw some footage of US navy Orion looking for the egyptian plane debris and you see this guy sitting in the plane with a whole wall of instruments in front of him and what was he doing? Drawing lines on a paper map with a pencil….

    Next day some more footage but this time the pilot, and next to him on the windowsill he had a small notepad and a pen holder and he made a note with the pen then put it back in the stand, while in front of him wall to wall instruments and digital screens.

    It’s an amusing thing. And it made me wonder if in case they found something a drone would come and attach a wire so they could telegraph the news :)

    1. With pen and paper it is difficult to make order of magnitude errors, so typical for malfunctioning digital systems. Believing in computer guidance proved to be a huge error for many who ended their gps trips in the lake, or in different country. Besides, the power can always go out. In that case, I’d rather be in Nieuport 17 than in an F-22.

      1. you forget that much of what aerospace has been doing for 40 years isnt possible without said computer control and it still seems to work quite well, not to mention the millions of people every year who land autonomously in commercial passenger liners.

        tbh i trust those computers a whole heck of a lot more than i do any pilot, statistically they will get sick from food or general illness quite a bit easier than a properly built and tested system fails, that is before we look at the quite literally dozens of other direct factors that might make a human the worse choice.

        1. “””i trust those computers a whole heck of a lot more than i do any pilot””” Well, those computers are programmed by people. Many of which don’t have a clue about fail safe mechanisms.

  5. I did my final year project on an ASR-33 connected to a Computer Automation mini. I can tell you that it was 7-bit ASCII but probably was still a current loop interface. I still have the code for my project on paper tape somewhere.

  6. I spent a good many years in the ’70s fixing those machines. The model 28 was a work of art, lovely to watch. The model 35 was the ASCII version – not as great a machine – they just speed it up and added a few more bits the poor clutches never stood a chance. The 32/33 were built to be cheap, you had to bend parts to make adjustments. They often became unrepairable after a couple techs had a go at them…

  7. I never got around to messing with old facsimile and teleprinter machines. Probable never will seeing there are modern less expensive alternatives to do the work they do.

  8. Not so old as teletype but I’ve been trying to find a full copy of 3D FAX. It takes computer files, converts them to a 2D ‘barcode’ then sends the images by FAX.

    The images can be received by a FAXmodem and decoded, or printed on paper then scanned into a computer and decoded.

    Dunno what kind of data density per page it could do. Would be somewhat nifty to have a file folder of printouts as a backup of something. 100% EMP proof, won’t self-demagnetize, cannot break, stretch or tangle like magnetic tape.

    1. I found a few awhile ago and never got around to trying them out! This one claims 3MB per A4 sheet using a compression algorithm on text files, but only about half a meg. for the average file. It has ECC of course. :)
      Search for ‘full page paper backup’ Hope this helps!
      If anybody has tried the program please leave a post. Tear the page and leave coffee stains on it; does the error correction work?

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