Texting With A Teletype

How do you get the kids interested in old technology? By connecting it to a phone, obviously. Those kids and their phones. When [Marek] got his hands on an old-school teletype, he hooked it up to a GSM network, with all the bells and whistles including a 40mA current loop running at an impressive 50 baud.

The teletype in question here is a vintage T100 teletype manufactured in Czechoslovakia sometime in the ’70s. This was a gift to [Marek]’s workplace, the museum of Urban Engineering in Cracow, and this project is effectively an experiment to investigate the possibility of running this teletype as an interactive exhibit rather than an artefact from the age of current loops and phone systems.

The current loop is, or was, the standard way of connecting a teletype to anything, so all [Marek] had to do was construct a box that translated the signals from a GSM modem to this current loop. For the prototype, the microcontroller in question is an old AT89C2051 (as that’s what was sitting in the parts drawer). This was moved over to a PIC32 microcontroller and a SIM800 GSM module. This is housed in a two-part enclosure, with the GSM interfaced housed in one half, with the current loop generator consisting of a simple DC power supply housed int the other half.

This interface is capable of receiving and sending messages from the keyboard to a GSM network, so it is theoretically possible you could text your friends using an old-school teletype. This functionality hasn’t been implemented yet, but it is just about the coolest thing you could possibly imagine. You can check out a video of the teletype in action below.

13 thoughts on “Texting With A Teletype

  1. Started learning BASIC at University of Utah in 1975. Paid a buck an hour for access to a row of teletype machines converted to I/O terminals connected to s Univac 1108. Will always remrmber that “shook shook shook” as you typed input and then rapid newroom clatter on printouts. Was also a DEC LA120 with pin printer and a Tek graphics terminal, but they were both usually busy all the time.

  2. And the current loop used in teletype networks was a throwback to telegraphy. Telegraph stations were wired in a loop so that one wire could be used for a number of stations. At each station, the wire went through the telegraph key and the coil of the sounder, then went on to the next station. This is why telegraph keys have shorting switches – all stations not transmitting had to leave their keys shorted to complete the loop. Same with teletypes – the keyboard’s output switch was closed when nothing was being transmitted, which allowed other stations to send. The “break” key, which survived even into CRT terminals, opened the loop, which would start the motors of all of the machines in the loop, to ensure they were up to speed before the transmission began. I remember using one computer (early 70s) that would detect break and generate an interrupt.

    Every technology has genetic residue from its ancestors.

  3. Neat to see that flying-key T100. Reminds me of the IBM Model B on our college’s IBM 1620. Mechanical breakdowns were frequent.

    We had Model 33 TTYs on our DEC PDP-7 and PDP-8 machines. Knowing too much about the Model 33 TTY was possibly damaging to a programmer’s career. Being mechanically adept, and having learned how to adjust the finicky “H-plate” of the Model 33, I was always the one called upon to perform the adjustment.

    All The Time.

    I could only get programming done when I wasn’t adjusting H-plates, or later, repairing broken Diablos or NEC Spinwriters with rubber bands and paper clips. On some occasions I lied, and denied knowing anything about TTYs.

    1. I repaired Model 33 machines for our University. The H-plate connected the keyboard to the typing unit (which had the motor and the parallel-to-serial converter “distributor” for the keyboard data). I spent my summers disassembling, cleaning and re-lubing our stable of ASR-33 machines.

  4. I learned to type on a T100-B in 1985 when I was in the army, there was already a 100-C and the daisy wheel one I think it was the 1000.
    Why the 100-B, it was the best mechanical tty in those days, the plastic 100-C s died quickly in the field (radiovan) but the 100-B’s kept going. Oiling them regularly is really needed, most office people forget this.

    Managed to do 140 letters a minute on it, the noise and movement of these things is epic.
    In 87 I started with computer stuff and I really had to unlearn the thumb operated letter.figure shift.

  5. I spent the first 2 years of my IT career at Western Union in Mahwah, NJ where I learned how to rebuild model 32 Teletypes, GE Terminets, ADM 100, and a few more. They even sent me to Teletype school in Skokie Illinois to learn to refurb model 40 Teletype printers. Remember taking a tour of their manufacturing line, lots of little old ladies doing the fine work and a huge wave soldering line where they allowed the bottoms of PC boards to gently touch vats of hot solder, sucking the solder onto connection points. Loved working with oil soaked paper tape. Our test tapes were made of mylar. Spent many hours out in the field, plugging a Datascope with tape cartridge into the Bankwire network looking for invalid command streams and watching millions of dollars of transactions taking place across the globe.

    1. 5555 W Touhy Av
      Chicago IL

      Teletype was a wholly owned subsidiary of Western Electric, something I did not know until I started working onh them. The Teletype manualshave the same formatting as the Bell System Practice documents.

  6. The nostalgia of clattering mechanical printers.
    I was an engineering undergraduate in the mid-70s so with the advent of the home computer all my available financial resources went towards the purchase of a PC. Great, unlike other students I now did not now to hunt all over campus, often late into the night, for that allusive not in use student accessible computer terminal.
    But how to get physical output from the computer at home? I needed a printer. A dot matrix printer was beyond my now depleted resources so surplus equipment appeared the way.
    I wanted something cheap that could print upper/lower case so a Baudot (5-bit code) teletypewriter, though available, would not do. Eventually, I managed to find a junked Friden 2200 series Flexowriter but what a mechanical nightmare. Basically a typewriter with a matrix of linkages and solenoids that actuate keys based on the code received. That I could get it to type anything was the accomplishment but other than that a failure for my purposes. Then I heard about a business that had obsoleted a computer terminal printer and was asking for offers. I ended up with an ASR33 and a full set of service manuals for a price within my means. That became my printer over the remainder of my study. Like other commentators, I also became an expert in teletype mechanical adjustments.
    But 10 CPS is slow, even if your time is free, and I eventually came across another source of surplus printing terminals – GE Terminet 1200s. These had a band printer mechanism. A belt with all the printable characters on it rotating past solenoid actuated hammers at every print position across the page. When a required character aligns with its required position on the line to print the solenoid fires. So one line at up to 120 CPS is printed for each rotation of the character belt. Still quite mechanical but potentially 10 times faster printing.
    Once graduated I had a job and money so what did I buy for my next computer printer – a Diablo daisywheel !! Finally, after a few more years I got onto the less mechanically based technology path and bought an HP Postscript Laser printer.

    1. So many years I spent looking for the ideal printer. First was a Centronics 102 that I built a serial to parallel converter to plug into my CoCo, then found a Selectric-based “word processor” that I was able to write a driver to connect to the same computer, giving me letter-quality printing. Then an IBM Executive that was fitted with solenoids, and then a Sears (Nakajima) typewriter that had a Centronics port. Eventually a mish-mash of lasers and inkjets. Now on the rare occasion when I need something printed on paper, I just go to Kinko’s. No looking back.

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