Casio Calculator Gets New Keyboard

February 1, 2025 by Al Williams 5 Comments

What do you do with a circa 1985 Casio FX-451 calculator with a bad keyboard? Well, if you are [Poking Technology], you transplant the inside of the calculator to a new custom keyboard. There are two videos that cover the process in detail, which you can watch below.

The calculator has a unique design. It looks like a simple calculator in a wallet. But the wallet opens to reveal an extended keyboard with all the scientific features onboard. Unsurprisingly, the membrane keys didn’t survive over four decades. Disassembling the unit was a challenge. Soldering wires to the keyboard lines was further complicated by the fact that some of the lines are on the back of the PCB and pass through to the top under the main IC.

The new keyboard is quite a bit larger than the original, making this more of a desk calculator, but that also means you can use high-quality keys. We’d love to see a 3D printed case to wrap it all up, but the bare PCB look has its charms, too.

If you can’t understand how [Poking] can love a calculator so much, you probably never owned an HP-41C, either. Of course, our retro calculator dreams also include Star Trek.

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A Mechanical Calculator For The Modern Age

December 26, 2024 by Jenny List 16 Comments

There was a brief period through the 1960s into the 1970s when the last word in electronics was the calculator. New models sold for hundreds of dollars, and owning one made you very special indeed. Then the price of the integrated circuit at their heart fell to the point at which anyone could afford one, and a new generation of microcomputers stole their novelty for ever. But these machines were by no means the first calculators, and [What Will Makes] shows us in detail the workings of a mechanical calculator.

His machine is beautifully made with gears hand-cut from plywood, and follows a decimal design in which the rotation of a gear with ten teeth represents the numbers 0 to 9. We’re taken through the mechanical processes behind addition, subtraction, multiplication, and division, showing us such intricacies as the carry lever or a sliding display mechanism to implement a decimal equivalent of a bitwise shift multiplication.

We have to admit to be particularly impressed by the quality of the work, more so because these gears are hand made. To get such a complex assembly to work smoothly requires close attention to tolerance, easy with a laser cutter but difficult by hand. We heartily recommend watching the video, which we’ve placed below the break.

Meanwhile if you’d like more mechanical calculators, take a look at one of the final generation of commercial models.

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close up of a TI-84 Plus CE running custom software

Going Digital: Teaching A TI-84 Handwriting Recognition

December 24, 2024 by Heidi Ulrich 4 Comments

You wouldn’t typically associate graphing calculators with artificial intelligence, but hacker [KermMartian] recently made it happen. The innovative project involved running a neural network directly on a TI-84 Plus CE to recognize handwritten digits. By using the MNIST dataset, a well-known collection of handwritten numbers, the calculator could identify digits in just 18 seconds. If you want to learn how, check out his full video on it here.

The project began with a proof of concept: running a convolutional neural network (CNN) on the calculator’s limited hardware, a TI-84 Plus CE with only 256 KB of memory and a 48 MHz processor. Despite these constraints, the neural network could train and make predictions. The key to success: optimizing the code, leveraging the calculator’s C programming tools, and offloading the heavy lifting to a computer for training. Once trained, the network could be transferred to the calculator for real-time inference. Not only did it run the digits from MNIST, but it also accepted input from a USB mouse, letting [KermMartian] draw digits directly on the screen.

While the calculator’s limited resources mean it can’t train the network in real-time, this project is a proof that, with enough ingenuity, even a small device can be used for something as complex as AI. It’s not just about power; it’s about resourcefulness. If you’re into unconventional projects, this is one for the books.

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Retro Calculator Build Proves The Space Age Isn’t What It Used To Be

November 14, 2024 by Dan Maloney 19 Comments

The common wisdom these days is that even if we wanted to get back to the Moon the way we did in the 1960s, we’d never be able to do it. Most of the blame for that usually falls on the loss of institutional knowledge thanks to skilled minds and hands that have been stilled by the passage of time, but the real kicker would be finding replacements for all the parts that we used back then that just aren’t made anymore. A similar problem exists for those seeking to recreate the circuits that graced the pages of the many magazines that catered to electronics hobbyists back in the day.

Take this “Space Age Decimal Computer” reproduction that [Bob Alexander] undertook. Smitten with the circuit after seeing our story about a 1966 article detailing its construction, he decided to roll one of his own. That proved to be far harder than he thought it would be. The original circuit, really little more than an adding machine using a rotary telephone dial as an input device, used neon lamp ring buffers for counting, The trouble is, while NE-2 neon lamps are still made, they aren’t made very precisely. That makes it difficult to build a working ring buffer, which relies on precise on and off voltages. That was even a problem back then; the author suggested buying 100 lamps and carefully characterizing them after aging them in to get the 60 lamps needed.

In the end, [Bob] settled for modifying the circuit while making the build look as close as possible to the original. He managed to track down the exact model of enclosure used in the original. The front panel is populated with a rotary dial just like the original, and the same neon lamps are used too, but as indicators rather than in ring buffers. Behind the scenes, [Bob] relied on 7400-series counters and decoders to make it all work — kudos for sticking with 1970s tech and not taking the easy way out with an Arduino.

The video below goes into more detail on the build and the somewhat kludgy operation of the machine, with a few excellent [Tom Lehrer] references and a nice Cybertruck dunk to boot.

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Solve: An ESP32-Based Equation Solving Calculator

October 15, 2024 by Dave Rowntree 10 Comments

We’re suckers for good-looking old-school calculators, so this interesting numerical equation-solving calculator by [Peter Balch] caught our attention. Based around the ESP32-WROOM-32 module and an LCD, the build is quite straightforward from an electronics point of view, with the main work being on the software side of things.

A custom keyboard was constructed on Veroboard using a handful of tactile switches arranged in a charlieplexing array to minimize the number of IO pins consumed. For the display, an off-the-shelf 240×320 ILI9341-based module hooked up by SPI was used. A single lithium cell was used for the power supply, connected to a USB

You don’t need much to make a usable keyboard.

charger module, but you could just as easily substitute a 3 x AA battery box. The case was designed in DesignSpark mechanical and 3D printed. It’s unclear what keyboard version they settled on; there are options for one with keycaps and one without. Regardless, a 3D-printed frame sits atop the keyboard circuit, with the graphics printed on photo paper and a protective coversheet on top. Continue reading “Solve: An ESP32-Based Equation Solving Calculator” →

A black OLED screen with a happy face displayed upon it is situated at the top of a squarish calculator with a 5x6 grid of white calculator keys. It floats above a graphing calculator, Nintendo Switch, aigo numpad, and an Arduino Mega on a white table. A handful of differently-colored kalih choc switches are in various places around the table.

Mechanical Switch Sci-Calc Is Also A Macropad

October 4, 2024 by Navarre Bartz 6 Comments

Smartphones have replaced a desktop calculator for most folks these days, but sometimes that tactility is just what you need to get the mathematical juices flowing. Why not spruce up the scientific calculator of yore with the wonders of modern microcontrollers?

While you won’t be able to use Sci-Calc on a standardized test, this classy calculator will let you do some pretty cool things while clacking on its mechanical choc switches. Is it a calculator? Obviously. Is it an Arduboy-compatible device that can play simple games like your TI-84? Yes. Is it also a macropad and ESP32 dev board? Why not? If that isn’t enough, it’s also takes both standard and RPN inputs.

[Shao Duan] has really made this device clean and the menu system that rewrites main.bin based on the program selection is very clever. Escape writes main.bin back into the ROM from the SD card so you can select another application. A few classic games have already been ported, and the process looks fairly straightforward for any of your own favorites.

If you’re hankering for more mathy inputs, checkout the Mathboard or the MCM/70 from 1974.

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Internet Connected TI-84 To Cut Your Academic Career Short

September 29, 2024 by Danie Conradie 22 Comments

In an educational project with ethically questionable applications, [ChromaLock] has converted the ubiquitous TI-84 calculator into the ultimate cheating device.

The foundation of this hack lies in the TI-84’s link protocol, which has been a mainstay in calculator mods for years. [ChromaLock] uses this interface to connect to a tiny WiFi-enabled XIAO ESP32-C3 module hidden in the calculator. It’s mounted on a custom PCB with a simple MOSFET-based level shifting circuit, and slots neatly into a space on the calculator rear cover. The connecting wires are soldered directly to the pads of the 2.5 mm jack, and to the battery connections for power.

But what does this mod do? It connects your calculator to the internet and gives you a launcher with several applets. These allow you to view images badly pixelated images on the TI-84’s screen, text-chat with an accomplice, install more apps or notes, or hit up ChatGPT for some potentially hallucinated answers. Inputting long sections of text on the calculator’s keypad is a time-consuming process, so [ChromaLock] teased a camera integration, which will probably make use of newer LLMs image input capabilities. The ESP32 doesn’t handle all the heavy lifting, and needs to connect to an external server for more complex interfaces.

To prevent pre-installed programs from being used for cheating on TI-84s, examiners will often wipe the memory or put it into test mode. This mod can circumvent both. Pre-installed programs are not required on the calculator to interface with the hardware module, and installing the launcher is done by sending two variables containing a password and download command to the ESP32 module. The response from the module will also automatically break the calculator out of test mode.

We cannot help but admire [ChromaLock]’s ingenuity and polished implementation, and hopefully our readers are more interested in technical details than academic self-sabotage. For those who need even more capability in their calculator, we’d suggest checking out the NumWorks. Continue reading “Internet Connected TI-84 To Cut Your Academic Career Short” →