calculator

143 Articles

Calculator Battery Mod Lets You Go The Distance

September 23, 2025 by 23 Comments

Disposable batteries seem so 1990s. Sure, it’s nice to be able to spend a couple of bucks at the drugstore and get a flashlight or TV remote back in the game, but when the device is a daily driver, rechargeable batteries sure seem to make more financial sense. Unfortunately, what makes sense to the end user doesn’t always make sense to manufacturers, so rolling your own rechargeable calculator battery pack might be your best option.

This slick hack comes to us from [Magmabow], who uses a Casio FXCG50 calculator, a known battery hog. With regular use, it goes through a set of four alkaline AA batteries every couple of months, which adds up quickly. In search of a visually clean build, [Magmabow] based the build around the biggest LiPo pillow-pack he could find that would fit inside the empty battery compartment, and planned to tap into the calculator’s existing USB port for charging. A custom PCB provides charging control and boosts the nominal 3.7-volt output of the battery to the 5-ish volts the calculator wants to see. The PCB design is quite clever; it spans across the battery compartment, with its output feeding directly into the spring contacts normally used for the AAs. A 3D-printed insert keeps the LiPo and the PCB in place inside the battery compartment.

Almost no modifications to the calculator are needed, other than a couple of bodge wires to connect the battery pack to the calculator’s USB port. The downside is that the calculator’s battery status indicator won’t work anymore since the controller will just shut the 5-volt output down when the LiPo is discharged. It seems like there might be a simple fix for that, but implementing it on such a small PCB could be quite a challenge, in which case a calculator with a little more room to work with might be nice. Continue reading “Calculator Battery Mod Lets You Go The Distance” →

Creating A New Keyboard Flex For An Old Calculator

August 12, 2025 by 20 Comments

[Menadue] had a vintage Compucorp 326 calculator with an aging problem. Specifically, the flex cable that connects the button pad had turned corroded over time. However, thanks to the modern PCB industrial complex, replacing the obscure part was relatively straightforward!

The basic idea was simple enough: measure the original flex cable, and recreate it with the flat-flex PCB options available at many modern PCB houses that cater to small orders and hobbyists. [Menadue] had some headaches, having slightly misjudged the pitch of the individual edge-connector contacts. However, he figured that if lined up just right, it was close enough to still work. With the new flex installed, the calculator sprung into life…only several keys weren’t working. Making a new version with the correct pitch made all the difference, however, and the calculator was restored to full functionality.

It goes to show that as long as your design skills are up to scratch, you can replace damaged flex-cables in old hardware with brand new replacements. There’s a ton of other cool stuff you can do with flex PCBs, too.

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8 Bit Mechanical Computer Built From Knex

July 20, 2025 by 24 Comments

Long before electricity was a common household utility, humanity had been building machines to do many tasks that we’d now just strap a motor or set of batteries onto and think nothing of it. Transportation, manufacturing, agriculture, and essentially everything had non-electric analogs, and perhaps surprisingly, there were mechanical computers as well. Electronics-based computers are far superior in essentially every way, but the aesthetics of a mechanical computer are still unmatched, like this 8-bit machine built from K’nex.

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An image of a light grey graphing calculator with a dark grey screen and key surround. The text on the monochrome LCD screen shows "Input: ENEB Result 1: BEEN Confidence 1: 14% [##] Result 2: Good Confidence 2: 12% [#] Press ENTER key..."

A Neural Net For A Graphing Calculator?

July 17, 2025 by 3 Comments

Machine learning and neural nets can be pretty handy, and people continue to push the envelope of what they can do both in high end server farms as well as slower systems. At the extreme end of the spectrum is [ExploratoryStudios]’s Hermes Optimus Neural Net for a TI-84 Plus Silver Edition.

This neural net is setup as an autocorrect system that can take four character inputs and match them to a library of twelve words. That’s not a lot, but we’re talking about a device with 24 kB of RAM, so the little machine is doing its best. Perhaps more interesting than any practical output is the puzzle solving involved in getting this to work within the memory constraints.

The neural net “employs a feedforward neural network with a precisely calibrated 4-60-12 architecture and sigmoid activation functions.” This leads to an approximate 85% accuracy being able to identify and correct the given target words. We appreciate the readout of the net’s confidence as well which is something that seems to have gone out the window with many newer “AI” systems.

We’ve seen another TI-84 neural net for handwriting recognition, but is the current crop of AI still headed in the wrong direction?

Continue reading “A Neural Net For A Graphing Calculator?” →

Repairing Vintage Sony Luggable Calculators

June 10, 2025 by 1 Comment

You might wonder why you’d repair a calculator when you can pick up a new one for a buck. [Tech Tangents] though has some old Sony calculators that used Nixie tubes, including one from the 1960s. Two of his recent finds of Sony SOBAX calculators need repair, and we think you’ll agree that restoring these historical calculators is well worth the effort. Does your calculator have a carrying handle? We didn’t think so. Check out the video below to see what that looks like.

The devices don’t even use modern ICs. Inside, there are modules of discrete parts encapsulated in epoxy. There isn’t even RAM inside, but there is a delay line memory, although it is marked “unrepairable.”

There is some interesting history about this line of calculators, and the video covers that. Apparently, the whole line of early calculators grew out of an engineer’s personal project to use transistors that were scrapped because they didn’t meet the specifications for whatever application that used them.

The handle isn’t just cosmetic. You could get an external battery pack if you really wanted a very heavy — about 14 pounds (6.3 kilograms) — and large portable calculator. We are sure the $1,000 retail price tag didn’t include a battery.

These machines are beautiful, and it is fun to see the construction of these old devices. You might think our favorite calculator is based on Star Trek. As much as we do like that, we still think the HP-41C might be the best calculator ever made, even in emulation.

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Soviet Calculator Teardown Reveals Similarities And Differences

June 6, 2025 by 12 Comments

Tearing down hardware from different parts of the world can be revealing, showing unique parts, techniques, and tricks employed by engineers living in a very different world from our own. To that end, [msylvain59] has been kind enough to give us a look inside the Elektronika MK-26—a calculator built in the former Soviet Union.

There’s lots of interesting stuff to see from the get-go. The oddball button pad is covered in Cyrillic symbols, quite alien to those of us more accustomed to the Latin character set. It’s also constructed somewhat unlike more familiar models from Western-aligned companies like Casio or Commodore. It also rattles when shaken, which doesn’t inspire confidence. Inside, it’s got old-school brown PCBs without the usual green solder mask, a chunky IC in a weird package, and display is via a power-hungry VFD.

It doesn’t look so totally alien inside; much of the construction is pretty typical of the mid-1970s, wherever you went around the world. The most striking differences are more in the graphics and visual design than anything else.

Ultimately, there are reasons why manufacturers around the world tend to converge on similar techniques. Generally, it’s because it’s more economical or easier to do things a certain way. And yet, we still see regional variances because conditions, technologies, and parts availability varies around the world. This teardown highlights that quite clearly.

If you’re just getting a taste for Soviet hardware teardowns, you’ll love this video diving inside a real Soyuz clock.

Continue reading “Soviet Calculator Teardown Reveals Similarities And Differences” →

Trekulator: A Reproduction Of The 1977 Star Trek Themed Calculator

April 21, 2025 by 9 Comments

A recent project over on Hackaday.io from [Michael Gardi] is Trekulator – Where No Maker Has Gone Before.

This is a fun build and [Michael] has done a very good job of emulating the original device. [Michael] used the Hackaday.io logging feature to log his progress. Starting in September 2024 he modeled the case, got his original hardware working, got the 7-segment display working, added support for sound, got the keypad working and mounted it, added the TFT display and mounted it, wired up the breadboard implementation, designed and implemented the PCBs, added some finishing touches, installed improved keys, and added a power socket back in March.

Continue reading “Trekulator: A Reproduction Of The 1977 Star Trek Themed Calculator” →