Early “Computer Kit” Really Just A Fancy Calculator

We’re big fans of calculators, computers and vintage magazines, so when we see something at the intersection of all three we always take a look. Back in 1966, Electronics Illustrated included instructions in their November issue on building, in their words, a “Space-Age Decimal Computer!” using neon lamps, a couple of tubes, and lots of soldering. The article starts on page 39 and it’s made fairly clear that it will be an expensive and complicated project, but you will be paid back many times over by the use and experience you will get!

Our modern idea of a computer differs greatly from the definitions used in the past. As many readers likely know, “Computer” was actually a job title for a long time. The job of a computer was to sit with pen, paper, and later on electromechanical devices, and compute and tabulate long lists of numbers. Imagine doing payroll for large companies completely by hand, every month. The opportunity for errors was large and was just part of doing business. As analog and later transistor-based computers started to be developed, they replaced the jobs of human computers in calculating and tabulating numbers. This is why IBM was originally called the Computing, Recording and Tabulating Company!

So at the time this article was written, the idea of a computer as just a number-cruncher meant that for the magazine readers, a machine that could add, subtract, multiply and divide was for all intents a computer. The kit is a fairly clever but simple machine. A rotary telephone dial is used to enter numbers from 1 to 10 (with the 0 acting as 10). This sends pulses into a series of boards that represent decimal decades from 1s all the way up to 100000s. You use a rotary switch to select which decade to enter a number into. And then, just like manual addition, you dial in the second number, working from the units upwards. All carries are done automatically, and you have your result after entering each addend.

As the machine can only count upwards, subtraction is done by adding complements. This is all based on doing the 9s complement of the number to be subtracted, and the article goes into a lot of detail on the operation of the machine. Tricks like these were common when using electromechanical machines and would have been familiar at the time to many readers. Of course, multiplication and division are repeated additions or subtractions, and with long inputs, it could become very tedious. However, as long as the machine was carefully constructed and each number carefully noted down, it could be a very useful tool that would eliminate errors!

Thanks to [Stephen] for the tip!

22 thoughts on “Early “Computer Kit” Really Just A Fancy Calculator

  1. I remember this article quite well but as a kid in the 60’s on a farm I didn’t have the money to build it. My older brother did get for Christmas that year the plastic version, well sort of, called a DigiComp.

  2. This artical set me on a path to become an EE. I built it and won a blue ribbon in the local science fair.
    I wish I could find some photos but the WABAC machine is broken. It did teach me about electronics and how things work. Still have that fire to this day.

    1. Indeed. A skim of the article seemed to suggest a need to build a test jig to characterize the neon bulbs, presumably for the purpose of finding matched sets. Get an outlier in one of those strings of 10 and it’d probably hang on that bulb (or the one before it?) and render the counter useless.

  3. Very interesting, I never knew about this project/article. However, in the mid 70s, when I was a Jr High school kid, I built something along these lines. Mine was based on scrap and Radio Shack parts, and built into a plastic “Battleship” case.

    Basically it was a large TTL counter driven by a rotary phone dial.

    Ironically, I remember it not because of the primitive computing aspect of it, but because it was my first encounter with contact bounce ( I had no oscope and had never heard of such a thing.)

    Initially, when I tried to dial a digit, the TTL counter went seemingly crazy. Through intuition and a few experiments (a had no oscope and couldn’t have dreamed of one) , I converged on a caveman’s solution– the phone dial drove a flashlight bulb, which illuminated a phototransistor tied to the input of the counter chain. The thermal mass of the flashlight bulb’s filament masked the contact bounce and the circuit always worked reliably.

  4. The whole magazine is fascinating, ads and all. Tubes aplenty, yet an article on “ICs Go Civilian” and a Motorola book of FET projects and another of Integrated Circuit projects. I was 2, and nine years later I built a crystal radio and entered the rabbit hole I still have not escaped from.

  5. I saw this article in junior high school and tried to make a flip flop out of neon lamps. No success, but this was my first hands-on experience with digital electronics. Learned much later that this method required finding pairs of neon bulbs with similar thresholds, after burn-in. I found what happened if you put AC current across the leads without a resistor: it instantly blows up, sending glass shards everywhere across the basement.

  6. This neon-bulb counter design was very similar to a detailed transistor-based design in the 1961 book “Computers! from Sand Table to Electronic Brain” by Alan Vorwald and Frank Clark. My grade school somehow had a copy. I couldn’t afford to play with transistors then, but the book set me up to want to build the neon-bulb version when this article came out.

  7. The January 1960 article of Electronics Illustrated had a similar construction article. The unit was a telephone dial driver counter. The counter was constructed with flip-flops made from power transistors. The article called the unit a computer, too. As a lad, I learned about binary arithmetic from the article.

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