An Old Calculator Lives Again

There was a time when any electronics student would have a slide rule hanging off their belt. By the 1970s, the slide rule changed over to an electronic calculator which was a pricy item. Today you can buy calculators at the dollar store. [JohnAudioTech] pulled out an old Radio Shack vacuum fluorescent display (VFD) calculator and found it didn’t work. Obviously, that means it is time to open it up.

It is fun to see one of these old devices opened up again. Consumer electronics with big through-hole ICs! Troubleshooting the device wound up being anti-climatic, as a broken wire to the battery compartment explained the whole thing.

As a teardown, though, this is a fun video. Not only are all the parts through-hole, but the PCB is clearly a manual layout with serpentine traces flowing across the board like some sort of art piece.

[John] even has a need hack for the calculator itself, if you happen to have one. Apparently, the calculator IC had a provision for a pi constant key, but there was no key for that function. Pressing the square root and 4 keys at the same time will trick the chip into providing pi anyway.

Another interesting item: [John] modified a cheap camera and removed the IR filter from it. Using that he was able to image the display’s cathode wire, which is normally difficult to see unaided.

There isn’t much need for a calculator now since your phone can easily do math ranging from a simple calculator app to symbolic math programs. But, like slide rules, we have a soft spot for these handheld computers.

If you don’t want vintage, an Arduino has plenty of power compared to these old machines. If, by chance, you want a modern calculator, they can also do plenty these days.

42 thoughts on “An Old Calculator Lives Again

  1. “By the 1970s, the slide rule changed over to an electronic calculator which was a pricy item.”

    Well, last time I bought a slide rule (a Pickett log-log trig model with about 20 scales), it cost me about $100. This was in 1980, and I also had a scientific calculator I bought in the late 70s that could do the same work at about the same price. The main trade-off, as I saw it, was that calculators at that point kind of burned through batteries, but they gave lots more digits of precision. Having learned since then how these calculators did their trig and log functions, though, the accuracy probably wasn’t much better than that of the slide rule. So really, price wasn’t the driving factor.

      1. PArt of it. But also, there are a lot of times when it is not convenient to use the phone as a calculator, like when you are doing your homework for physics and looking at the solution guide on the phone. Or, as a professional, using the phone for communication while running numbers on a calculator. It is not always desirable, or practical, to change applications.

        Other reasons, as well, that the stand-alone units haven’t gone away, and are likely to last for a good while longer. I remember when sliderules were on the way out and the screams of ” the batteries! the batteries!” or “you don’t need to plug in a sliderule”. sliderules lost in large part because the electronic unit was a direct replacement that beat it on nearly every measure. Not there yet with the smartphone, due to the smartphones versatility: too many other competing tasks

        Give it a few years, though.

        1. I really think calculators could still be relevant in professional and everyday home use if they had more models with better connectivity, and none of the educational limitations.

          There’s a whole class of device that’s kind of like what a phone does, but much lower power. Your calculator could be a flashlight, alarm clock, offline Wikipedia (Assuming SD card support), digital walkie talkie, home automation controller, weather station viewer(Just add LoRa/FSK radios), datalogger/multimeter/general tricorder like device/etc, TV remote, etc.

          A $50 to $100 device, if it was open and standardized and had WiFi, could fill the “Default choice of platform to control stuff” that a phone does, while also lasting months to years between charges or even being practical to use on solar power(Sharp Memory LCDs, plus no need for smartphone level OSes and connectivity).

          If it had a whole lot of power to it(2x 18650s or better yet the LTO18560 variant that’s good for decades), expansion modules could power robotics, solenoid valves, or whatever else, almost like Lego’s Mindstorms.

          You could even use an analog thumb stick for the UI, and have it be an acceptable RC car controller.

          Think of all the crappy Bluetooth multimeter and sensor add ons, USB Android thermal cameras, etc, and how awesome they could be if they securely mounted to the front of a device that was cheap enough to have a few dedicated to different things, and could be left in a drawer for a year switched off, and still be ready in seconds.

          Calculators are probably farther behind their potential than almost anything else these days.

          1. why you can buy a cheap android phone without service for 25 bucks at walmart, boom everything you just said and no one had to make a special device…. that would end up just being a cheap smart phone

        2. Reasons Why a Slide Rule (and Paper Pad) is Better Than an X Workstation

          – A Slide Rule doesn’t shut down abruptly when it gets too hot.

          – One hundred people all using Slide Rules and Paper Pads do not
          start wailing and screaming due to a single-point failure.

          – A Slide Rule doesn’t smoke whenever the power supply hiccups.

          – A Slide Rule doesn’t care if you smoke, or hiccup.

          – You can spill coffee on a Slide Rule; you can use a Slide Rule
          while _completely_submerged_ in coffee.

          – You never get nasty system messages about filling up your entire
          paper quota with pointless GIF pictures for the root window.

          – A Slide Rule and Paper Pad fit in a briefcase with space left over
          for lunch or a change of underwear.

          – A properly used Slide Rule can perform pipelined and parallel
          operations. (Okay, you need a guru for this.)

          – You don’t get junk mail offering pricey software upgrades that
          fix current floating point errors while introducing new ones.

          – A Slide Rule doesn’t need scheduled hardware maintenance.

          – A Paper Pad supports text and graphics images easily, and can be
          easily upgraded from monochrome to color.

          – Slide Rules are designed to a standardized, open architecture.

          – You can hold a Slide Rule at arm’s length, to hit the obnoxious
          person at the next seat over.

          – a Slide Rule is immune to viruses, worms, and other depradations
          from hostile adolescents with telephones.

          – Additional Paper Pads can be integrated into the system seamlessly
          and without needing to reconfigure everything.

          – Nobody will make you feel bad by introducing a smaller, faster,
          cheaper slide rule next month.

          from the frustrated, system-crashed desk of


      2. My syllabus–which all students agree to, and sign–states that the use of any electronic device, of ANY kind during an exam / test results in an automatic ‘zero’ for that exam. Twice, and student is dropped from course, with an ‘F’ (really somewhat irrelevant, as two ‘zero’s guarantee an ‘F’ anyway; just don’t have to put up with someone who flouts rules, after that).
        Oh, and I’ve already fought–and won–THIS battle with the administration, at the whining of poor, imposed-on students who consider it their right to not have to THINK; and a form of ‘cruel and unusual punishment’ to be taught to think, as a part of the education process.

        Similar restrictions (only difference is automatic expulsion) exist regarding the use of a “cellphone” during class. Only allowed if the student is participating in a call because of being on an Organ-Donor list, or a death in the family. It’s really quite calming to be able to lecture, to say nothing of being able to teach in a much more productive manner, without having cell-phones interrupting ME.

        1. Interesting. So you believe that being the provider of a service (whatever information you are imparting) gives you the power to enforce rules on your CUSTOMERS. Enjoy it while you can, dinosaur.

  2. There isn’t much need for a calculator since your phone can easily do math? That’s completely false!

    I keep a few calculators scattered around at my business because they are cheap and efficient. If I need to do much more than simple math I just grab one and use it. In comparison, using the calculator on my modern Samsung Galaxy Smart Phone involves pulling out the phone, logging in, scrolling to and then launching the app. Just getting to the app takes more time than getting the results I need from a basic low cost calculator!

    A $8.00 STAPLES SPL-240 calculator is much, much more efficient.

    1. I bet that makes a lot of sense for a professional engineer. As a hobbyist? Well, step 1 would be finding the calculator as I use it so infrequently it’s usually buried under a lot of clutter. I could almost write a calculator app from scratch faster. OTOH, my HP48G, which has long since gone to a trashy grave due to a broken screen is perfectly emulated on both my phone and desktop computer. It even runs the actual ROM legally as HP themselves made it a free download.

      It’s nice I can still have the same interface I grew up with. Or for simpler non graphing applications there is a mode where it only shows the more basic buttons allowing them to be bigger. But it’s on a device I can always locate and is usually already with me.

      Of course, for the really basic math having all your tables memorized is best!

      1. I have Emu48 and other calculator apps on my smartphone but I can grab my HP 48G, turn it on, do the calculation, turn it off, and put it down faster than I can get my phone out and launch the app on my smartphone. I’m impatient and I’ll use the tool that gets the job done quicker. I also prefer the dedicated physical user interface of the 48G because I can find and press the physical buttons much faster and more accurately so, again, it allows me to get my results quicker.

        I use my 48G all the time as a professional engineer. As a hobbyist, I use it all the time for all kinds things ranging from serious like financial calculations to silly like product output rates in Factorio.

      2. I struggled thru school on math. Tested in 4 grade at the university they couldn’t figure out my problem. Then recently I heard that they newly identified a subset of dyslexia that is all about numbers or as I call them numb-ers. Then I see an article in a 1930’s Pop-Sci zine that had the tongue twisting name all ready identified. Human memory is fallible and those “tables” of torture useless. Give me a calculator every time, money materials etc are at stake.

        The calculator – computer was invented because of human made copied and then typeset tables were suspect.
        I have a gripe with the education system that exempts a child with a physical problem from phys-ed but but doesn’t allow for my problem in grade school and on up.

  3. Why did no company integrate a basic calculator into a TV remote? Put in a calc chip, add a display and a button to toggle various non-number buttons to work as + – x / =. Mass produced the cost addition would be minimal.

    1. TV Remote, thermometer, wireless humidity sensor reciever, calculator, they’re all just batteries, a chip, a screen, buttons, and one or two parts specific to the application.

      Instead of trying to make smartphones the universal do-everything device, we could just as well have calculator-sized ESP32 handhelds, with an expansion port on the front for whatever you need the thing to do, which would also contain the flash chip that tells it how to do it.

      Standardized(Assuming the display you use exists in ten years), hackable, modular, instantly understandable to anyone who ever used a Gameboy, and only minimally more expensive than a single purpose machine.

      Design a few different standards, so when you get a TV, maybe you get the cheap one without a display and fixed function buttons, but then you can take the cartridge out
      and put it in a better device for Harmony remote style features.

  4. It’s 1975 and I’m starting electronics courses (including tube theory) at the local community college. We are told to purchase a suggested HP scientific calculator but it is way outside my budget. Sears is offering the APF Mark 51 calculator at an affordable price. I pick one up and use it at college for the next two years. I still use it today, still works perfectly. I does struggle to perform trig functions and you can count the seconds it takes to do some of those trig functions… yes I said seconds!

  5. You’re saying that instead of having the phone do everything, you could have the calculator do everything?

    So, you have a calculator which keeps time, has a screen, expandable modules, WiFi and bluetooth. Congrats, you just invented the computer! Then you add a battery, a flashlight, a walkie talkie, you make it portable, you control other things with it. Congrats, you just invented the smartphone!

  6. I saw the picture at the top of the article and immediately thought “Ah yes, the days of PC layout with tape and stencils”

    I never did any of that myself, being the first generation that started entirely in CAD, but I knew some of those layout guys at some of my early jobs, and was always amazed at what they were able to do with a roll of chartpak tape.

    I can only imagine the frustration of laying out a board by hand when you can’t simply drag and slide a net. If you need to fit in just one more trace you might have to – literally – rip up and reroute half your board into a big ball of sticky.

  7. I still regularly use my Casio FX3600P — The P is for programmable, with 32 steps memory. It ran on a single CR2032 cell, and the battery lasted about 2 years even when I was using it regularly. And, BTW, I purchased it used in 1981 and is still functioning as my main calculator…

  8. I had a slide rule when I started university in 1974 .. but it was quickly replaced by a kit Sinclair Scientific calculator, which despite having a bunch of accuracy issues – log(2) being awfully popular in Electronics, and remembering the calculator trying to tell me it was .30111 was a little off the more accepted answer of 0.30103, was much better. I had that calculator for my entire Uni course, only replacing with a fancy Japanese calculator with dot matrix LCD when I started work. There were some HP calculators bolted down to the desks in the library at Uni for accurate stuff, or I could use some of my precious interactive CPU time on the local ICL mainframe of course …

    I still have the slide rule. Never once have its batteries leaked.

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