Logging Into Linux With A 1930s Teletype

Buried deep within all UNIX-based operating systems are vestiges of the earliest days of computing, when “hardware” more often than not meant actual mechanical devices with cams and levers and pulleys and grease. But just because UNIX, and by extension Linux, once supported mechanical terminals doesn’t mean that getting a teletype from the 1930s to work with it is easy.

Such was the lesson learned by [CuriousMarc] with his recently restored Model 15 Teletype; we covered a similar Model 19 restoration that he tackled. The essential problem is that the five-bit Baudot code that they speak predates the development of ASCII by several decades, making a converter necessary. A task like that is a perfect job for an Arduino — [Marc] put a Mega to work on that — but the interface of the Teletype proved a bit more challenging. Designed to connect two or more units together over phone lines, the high-voltage 60-mA current loop interface required some custom hardware. The testing process was fascinating, depending as it did on an old Hewlett-Packard serial signal generator to throw out a stream of five-bit serial pulses.

The big moment came when he used the Teletype to log into Linux on a (more or less) modern machine. After sorting out the mysteries of the stty command, he was able to log in, a painfully slow process at 45.5 bps but still a most satisfying hack. The ASCII art — or is it Baudot art? — is a nice bonus.

We love restorations like these, and can practically smell the grease and the faint tang of ozone around this device. We’re not thrilled by the current world situation, but we’re glad [CuriousMarc] was able to use the time to bring off a great hack that honors another piece of our computing history.

Thanks for the tip, [Alex]!

47 thoughts on “Logging Into Linux With A 1930s Teletype

  1. Nothing like the rhythmic sound of an old Teletype. Of course, it does get old after a while. But you do have to respect the engineers who converted serial data to printed text totally mechanically. They’re marvels of engineering.

    1. QUOTE “Nothing like the rhythmic sound of an old Teletype. Of course, it does get old after a while. ”
      I heard that sound for thousands of hours from 1945 (When my Dad brought me to his office, next to the AP teletype (model 15) in the WELI newsroom, through many radio stations I worked at. The unusual bulletin sound brought me running (The Model 15 has a BELL character that mechanically rings a bell; it’s loud!). TEN BELLS was the AP and UPI standard for a BULLETIN coming in, reserved for very important messages. I remember so well the three instances of 10 bells, the day John F. Kennedy was assassinated :-(

      I still have a few spare parts for the model 15. For several years 1964-1974 I was an on-call repairman for the Associated Press in the Hudson valley. I diagnosed / repaired both model 15’s and Model 20’s (Those had upper and lower case and there were typically 4 or 5 of them in a newspaper newsroom). Lots of oil on my hands :-)

      About 1973 I traded a nice new Ampex consumer type tape audio system to the AP regional maintenance manager for two Teletypes: a Model 19 (Which is a model 15 with tape reader and punch) and a Model 33: The “new ASCII 100 baud machine”. I designed and built a Modem (Significant Analog and Digital electronics education) and was successful in dialing into the Dartmouth college time-sharing system on the line that SUNY used. I learned BASIC and a little FOFTRAN. The model 19 went to my Dad who used it on Amateur Radio RTTY with a ST-6 interface he built from parts. When I built my first 6502 based homebrew computer the first thing I wrote, in assembler, was a RTTY translator where he, on the model 19 and I on the Model 33 ‘talked’ every Sunday morning for many years. Eventually we converted to computers. And I went from Broadcast Engineering to IBM…

      Wow, I hadn’t thought about this stuff for years. Ancient history still in a rack in my barn: His ST-6 and my homebrew modem. Now I talk to my Grandchildren on Skype about the robots they are building…

      Thanks for the memories…
      Regards, Terry KIng …In The Woods In Vermont

      1. Thanks for sharing your memories, Terry – I enjoy hearing the tales from folks who had first-hand experience with the tech that’s a little before my time. Do you know what time sharing system you would have been dialing into? It’s crazy to think how patiently and accurately you had type when wrong answers would come back at 100 baud.
        I have in my (very long) restoration queue, both an ASR-33 and a model 15. The 33 appears complete, while the 15 is shy some crucial parts. There are about 3 or 4 Oscilloscopes in line in front of them – if they make it out of storage before the year is up, I’ll consider it a major accomplishment.

    1. I (a different Paul) owned both a ASR 33 and a much older Model 15 (like the one in the video). Both worked fine on both my Vic-20 and Apple ][. I sold the ’33 and threw the ’15 off a cliff. Very satisfying.

        1. A former cow-orker told me that once he took an old IBM PC, keyboard, and monitor up to the roof, plugged them into extension cords, booted it, and tossed them off.
          He made sure the extension cords were long enough to keep it running until impact.

        2. Yeah, Officer Obie is going to find my name on an envelope at the bottom of that pile of garbage and get twenty-seven 8×10 color glossy pictures with circles and arrows and a paragraph on the back of each one explaining what each one was, to be used as evidence… Because that’s about how long ago that was.

    2. When we got married (a *long* time ago) my wife and I were pelted with the yellow chaff from many ASR33 tape punches :-) Even worse, someone got hold of some mylar chaff from some “long-term” tapes. Still married; still occasionally picking out chaff from our filing cabinet of same vintage!

      1. Omighodd. Mylar chaff. Horrible stuff. We ran some Mylar tape through the punch on a PDP-7 once. “We plan to add floating-point hardware to this machine. Looks like we already have the floating points.”

      2. As kid i loved tapes and that chaff from my fathers work teletype. We did origami like chrismas tree ornamets from that tape he had mainly yellow but also blue and white.

  2. I know that sound. Back when I was knee-high to a grasshopper, my father had a similar teletype hooked up to his HF ham radio. I remember many nights actually falling asleep listening to that ridiculous, glorious mechanical racket.

  3. Even as a guy who’s used linux self taught for the last 15 years as my main OS, gotta say that’s peak nerdy. I can’t believe someone actually did this, but I’m impressed at how much harder they wanted to make logging in!

    45.5bps should be enough for anyone, hahaha

  4. And I thought my 300 baud modem was slow back when I phoned into the college computer! Finally moved up to 2400… Blazingly … still slow :) .

    That is really neat. Enjoyed the video. It brings back memory of programming on teletypes in high school computer lab. Reams of paper went through! At least we had a ‘full’ keyboard of characters to work with!

    1. Back in the day I briefly used a 2400 modem for websurfing. It wasn’t as bad as you would think (Back then anyway with 10kB rather than 10MB pages) Though I had found out how to turn on all the MNP5 compression goodies so it did about 9600 throughput. I was actually underimpressed when I clapped in the bargain basement 14.4 to replace it, which I didn’t not find out the right init strings for for weeks and weeks, so it was in bare 14,400 that’s all you get mode.

      1. In May of 1995 I bought an ISA 2400 baud modem used for five dollars. It was in ternal, I needed external. So I removed the UART, and added line drivers and receivers, thus bypassing the ISA interface and UART. Workedfine.

        A few months later I bought a used. USR 2400 modem, that had some sort of boost (I can”t remember what it was called) and the BBS and later ISP was compatible, so it was zippy.

        I moved to 14.4K in Nov 1996.

        I knew someo ne who had a 9600 baud modem,a brief sidestep on the consumer market.

  5. And then you have to learn “ed”, and you’re done!

    TBH the Arduino Mega he was using – just as the baud converter – probably has more compute power than the PDP-11/44 we used to use in the Computer Science dept at Durham.

    1. Yes. I was wondering why he didn’t just make a 5bit driver for linux, rather than a separate computer.

      In the seventies there were various articles in the hobby computer magazines abkut using 5bit TTY machines with computers. Someone modified a Tiny Basic. But I don”t recall external converters. Probably too expensive, but it also shows those “primitive”coukd do it all.

      1. The 8250 UART used in the PC supports the needed for 5N1.5, so linux lets you do that… or at least 5N2 (stty /dev/ttyS0 cs5 cstopb). However, I don’t know how many non-internal-PC UARTs will support these.

        I can even set mine to 45 or 46 baud, but the relevant IOCTL (TCSETS2) takes an integer, so 1% error is unavoidable.

        1. That’s a point.

          Of course, in the old days some computers used software to convert to and from serial, and thus no hardware UART. But that requires interrupts, and I”m not sure how such a driver might fit into Linux.

    2. AVRs are meant to be capable of a MIP per Mhz, so given PDP-11s topped out around 2 MIPs without 3rd party accelerators, it could be up to 10x as fast (With external 20Mhz Xtal)

  6. So, now he’s going to have to learn TECO in order to enjoy the full vintage experience. BTW, where on earth do you find ribbons and rolls of teletype paper any more? I don’t think Office Max carries them…

    1. I noticed fax paper was still available like that about 5 years back, haven’t looked again since. Ribbon could be pretty generic typewriter type, which is still available.

      1. Also, the ribbons were cloth and had long life. So one could reink them. Or if in decent shape, squirt with WD-40 and let it soak in, that’s a TTY era trick for dry ribbons.

        The paper might be trouble. It’s just a roll, no sprockets. Fifty years ago they’d be available from surplus stores, but I’ve never seen it in statiinary store catalogs.

        It’s the sort of paper Jack Kerouac used in his typewriter to write “On the Road”.

  7. “What were you arrested for, kid?” and I said, “Littering.” And they all moved away from me on the bench there, and the hairy eyeball and all kinds of mean nasty things, till I said, “And creating a nuisance.”

  8. My first job (1980) after school was in a suburban bank branch. They had two Olivetti teletypes to communicate with the bank’s computer in the nearest city.


    I never got to use them (me and the banking industry didn’t get along), but I remember one teller being told off by the supervisor to stop hitting the keys so hard – and rightly so – that guy was really belting them out. He came from another branch, presumably they had faulty/worn out keyboards that needed whacking.

  9. I was a rtty team chief in the National Guard in 1972-1985. I picked up a TT-98 and a TT-76 in the MARS program. Had 1 in the back porch and the other in the garage. My 8 and 10 year old girls would send messages to each other for hours. (Their spelin got more better). I used them for Rtty with a tnc until I replaced them with a Radio Shack model 1 computer. When we were on the air with an AN/GRC-19 (angry 19) we would send test messages that included a mechanical component… Some girls like to hug and kiss but my girl likes to do just this…LTRS FIGURES LTRS FGRS LTRS FGRS. These comments sure brought back some good memories!

  10. Back in the ’70s I had an old Model 19 for a while until I built an 8080-based computer and needed an ASCII machine. I found a guy who was willing to trade my 19 for a Model 33! My wife forbid me from using it after the kids went to bed… The machine made to much noise and would wake them up!

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