Reverse-Engineering Helps Typesetting Machine Punch Paper Tape Again

[Scott M. Baker] wants a paper tape punch for his retrocomputer collection. That’s fine with us, we don’t judge. In fact,  these electromechanical peripherals from the past have a lot going for them, especially the noise. But alas, such things are a little hard to come by these days, and rolling one from scratch would be a difficult proposition indeed. What to do?

Luckily, we live in the future, and eBay holds all sorts of wonders, including these typesetter keyboards from the 1970s, which [Scott] promptly reverse-engineered. We’ll get to the details in a minute, but first, can we just take a moment to think about the workflow these things were part of? These aren’t terminals — they lack any kind of IO apart from the punched paper tape they spewed out. The operator’s job was to punch in copy without any kind of feedback that they were hitting the right keys, and just sent the paper tap record of the session off to the typesetting machines. And you think your job sucks.

To give this thing an interface, [Scott] first had to revive the power supply, whose capacitors had seen sunnier days. With that out of the way, he set about understanding the CPU-less machine by analyzing its 7400-series logic, as well as planning how to make the native 6-bit output into a more manageable 8-bit. Thankfully, the tape punch already had solenoids for the top two bits, but finding a way to drive them wasn’t trivial.

The solution was to bypass a buffer so that the bits for the desired character can be set with a Raspberry Pi and an ATF22V10 programmable logic device. That’s enough to force the punch to do its thing; actually getting it to talk to something else, perhaps even [Scott]’s Heathkit H-8 computer.

11 thoughts on “Reverse-Engineering Helps Typesetting Machine Punch Paper Tape Again

    1. Interesting question. I should imagine it is available somewhere, likely by special order. The last source I used (post Y2K, but Not by much) is no longer. There is a good stock of legacy equipment that uses it, Numeric control manufacturing machines in particular, but little in the US or “first world”, so one might need to go to a source in the far east or Africa, where more such gear is still in service. I still have a roll of Polyester NC tape (same purpose, same dimensions, same feed perfs, but much, much tougher, and a bit thicker. Some readers and most punches made for paper had difficulty) Plain paper, without the feed perfs, is available easily, but I don’t know off hand how one would perf it, and it will be on rolls, which some gear can’t deal with, being made for fanfold only. Industrial gear generally handled rolls. Its been a good number of years since I spliced up a loop for a classic NC machine, and that was for a demo.

    2. You really can’t. That was the end of my dream to corner the paper tape punch market with my machine. I have 2 rolls in stock and I’ve run into a few people on the vintage computer sites that are hoarding the stuff, but no new stock to be had (that I could find)

      We (the vintage computer crew) even talked about commissioning a run of the stuff, but there isn’t enough interest in the final product. I offered to punch tape for free using modified cash register tape, and there were zero takers.

      1. The biggest problem is getting the right amount of oul in the paper. A lot of punchers need lubricated paper to help with wear on the punch blocks. I once used a table saw to cut the right width out of A2 paper on al roll. I only used it once.

        Oh and telex machines have the same problem.

    3. Wouldn’t calculator paper work? Those are still around, just carefully cut a new roll to correct size.

      If stiff paper is required, then I have no idea what can work.

    4. Oh gosh. Does this bring back memories. Did that in High School, 1976, teletype with 300 baud handset cradle modem to an HP 3000 system with timeshare BASIC. Later at a company that made a funky little 16-bit discrete TTL mini- computer, re-wrote in assembly and did the same thing… Labeled my technician shelves with it. Our test engineer at the time had absolutely NO clue as to how I did it… LOL!

  1. It doesn’t seem that difficult to make a paper-tape punch from scratch, assuming you’ve got a machine shop and solenoids and your usual stock of machine-making parts (stepper motors, drivers, controllers, extruded rails & hardware). The main difficulty would be producing the punch block and punches and hooking them up to the solenoids. Beyond that, you just need a sprocket hooked up to a stepper to feed the paper, a take-up spool if you’re making long output, a chaff collector, and some control logic.

    Readers are much simpler: just a bunch of LEDs and optical sensors in an appropriate housing, and it can read as fast as you can pull the tape through.

    1. you could probibly find a rolled paper tape product you can convert over. things like paper drywall tape (self adhesive fiberglass tape seems to have replaced it, but a quick google search found some). im not sure its properties are suited to punch tape though, its kind of thin, flimsy and may be too rough and fibrous. but there might be another product out there which is suitable.

  2. Brings back memories of learning to program in Basic in high school on a teletype Model 33 terminal with paper tape storage and a current loop interface to a 300 baud phone model to a DEC timeshare machine. These days, it is trivial to throw a microcontroller at just about anything. Figuring out the mechanical complexity of a model 33? Not a chance!

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