Ask Hackaday: Do We Need A 21st Century Calculator?

May 14, 2026 by Al Williams 80 Comments

The HP-41C analog on my phone gives the right answer.

Three resistors in parallel: 4.7 k,Ω 22 kΩ, and 3.3 kΩ. Quick! What’s the equivalent value? You can estimate it, of course, but if you want the actual 1.8 kΩ (approximately) answer, you probably reached for some kind of calculating aid. I have two slide rules on my desk, and plenty more a few steps away, but I don’t use them much, honestly. I have a very old HP-41C — arguably the best calculator ever made — but I am usually afraid to use it as it is almost 50 years old and difficult to repair. I also have an HP-28S on my desk, a replica HP-41C, and a few others in desk drawers. There are also dozens of calculators on my desktop computer, my phone –including the official HP Prime app — and the web browser.

I often see newer calculators from HP, like the Prime G2, or “new” HP-like calculators like the ones from SwissMicros, and think I should pick one up. Well, technically, HP licensed their calculators to Moravia, so even a “real” HP calculator isn’t from HP anymore. But, in the end, I always realize that my need for a physical calculator is so diminished that I can’t justify buying anything new, and I can barely even spring for a $10 one at the thrift store unless it is a real collectible.

Mind you, I’m not talking about RPN versus algebraic. I could say the same thing for TI, Casio, or Sharp calculators. I just don’t know why I need one anymore, even though I still, for some strange reason, want them.

The Prime seems impressive, if I could ever find time to finish reading the manual.

For the record, I did use an HP-41C to check the resistor math, but it was in the form of an app on my phone, not a real calculator. On the same computer I’m writing this on, I have HP-41C emulators, the Prime emulator, and a bunch of other calculators. Yet I still pick up my phone and use the familiar key layout of the HP-41C. I don’t know why. The replica 41C, unfortunately, has a landscape-oriented keyboard, so while I like it, it doesn’t satisfy my finger’s muscle memory.

Which leads to this Ask Hackaday. Do you use a calculator? Why? If you don’t, do you use a fake calculator on your phone or computer? Or do you just send your math to Google or Wolfram? I suspect some of the answer will be generational. I was in high school before calculators started showing up in schools, but they took over quickly.

There is something satisfying about having a purpose-built device to do your math. No long boot sequence. No switching apps. No messages coming in while you are typing in numbers. For the ultimate convenience, you could wear it on your wrist. The Apollo mission that docked with a Russian spacecraft carried an HP-65, and nine early Space Shuttle missions used an HP-41C. But even astronauts now don’t have a standard-issue calculator. Pilots sometimes use electronic E6Bs, but many still use the mechanical version.

Of course, I do collect slide rules, so maybe I just need to accept that calculators are yet another tech relic to collect. But someone is still buying them. I’d like to be one of them.

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Build The CPU, Then Build The Calculator

May 13, 2026 by Jenny List 21 Comments

It’s possible that among Hackaday readers are the largest community of people who have designed their own CPU in the world. We have featured many here, but it’s possible that not so many of them have gone on to power an everyday project. Step forward [Baltazar Studios] then, with a scientific calculator sporting a self-designed CPU on an FPGA.

The calculator itself is nice enough, with a smart 3D printed case, an OLED display which almost evokes a VFD, and very well made buttons. But it’s the CPU which is of most interest, because while it follows a conventional Harvard architecture with a 12-bit instruction set, it works with 4-bit nibbles. This choice follows one used by HP in their calculator designs, seemingly because it can be optimised for the binary coded decimal which the calculator uses.

With calculators being yet another app on our spartphones or comnputers, there seems to be less use of calculators outside of education in 2026. But if you are a calculator user there’s nothing like a calculator you made yourself, and with a CPU of your own design it has few equals. We like this project almost as much as we like the Flapulator!

A 3D-printed, split-flap display-having calculator with a Raspberry Pi Pico inside.

By Our Calculations, You’ll Love The Flapulator

April 14, 2026 by Kristina Panos 5 Comments

Oh sure, you’ve got calculators. There’s that phone program of course, and the one that comes with your OS, and the TI-86 and possibly RPN numbers you’ve had since high school.

But what you don’t have is a Flapulator, at least not until you build one. Possibly the be-all, end-all of physical calculating devices, the Flapulator does its calculating live on a split-flap display. It’s kind of slow and the accuracy is questionable, but the tactility is oh, so good.

This baby boasts a 6-digit display, where the decimal point and negative sign each require one digit. Inside is a Raspberry Pi Pico, which can calculate for around 4 hours on a full charge. But the coolest part (aside from the split-flap display, naturally) has got to be the 24-key, hand-wired mechanical keyboard. There’s also a couple of LEDs that light up to keep track of the current mathematical operation.

The story behind this one is kind of interesting. [Applepie1928] found out that one of their favorite mathematician-comedian-pi-lovers who is known for signing calculators was coming to town. With four weeks to whip something up, this was, amazingly, the result. Check it out in action after the break.

Need something that’s a whole other kind of fancy? Here’s an open-source graphing calculator.

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Build This Open-Source Graphics Calculator

March 23, 2026 by Zoe Skyforest 28 Comments

Graphics calculators are one of those strange technological cul-de-sacs. They rely on outdated technology and should not be nearly as expensive as they are, but market effects somehow keep prices well over $100 to this day. Given that fact, you might like to check out an open-source solution instead.

NumOS comes to us from [El-EnderJ]. It’s a scientific and graphic calculator system built to run on the ESP32-S3 with an ILI9341 screen. It’s intended to rival calculators like the Casio fx-991EX ClassWiz and the TI-84 Plus CE in terms of functionality. To that end, it has a full computer algebra system and a custom math engine to do all the heavy lifting a graphic calculator is expected to do, like symbolic differentiation and integration. It also has a Natural V.P.A.M-like display—if you’re unfamiliar with Casio’s terminology, it basically means things like fractions and integrals are rendered as you’d write them on paper rather than in uglier simplified symbology.

If you’ve ever wanted a graphics calculator that you could really tinker with down to the nuts and bolts, this is probably a great place to start. With that said, don’t expect your local school or university to let you take this thing into an exam hall. They’re pretty strict on that kind of thing these days.

We’ve seen some neat hacks on graphics calculators before, like this TI-83 running CircuitPython. If you’re doing your own magic with these mathematical machines, don’t hesitate to notify the tips line.

How HP Calculators Communicate Over Infrared

January 27, 2026 by Zoe Skyforest 11 Comments

For most people, calculators are cheap and simple devices used for little more than addition and the odd multiplication job. However, when you get into scientific and graphical calculators, the feature sets get a lot more interesting. For example, [Ready? Z80] has this excellent explainer on how HP’s older calculators handle infrared communications.

The video focuses on the HP 27S Scientific Calculator, which [Ready? Z80] found in an op-shop for just $5. Introduced in 1988, the HP-27S had the ability to dump screen data over an infrared link to a thermal printer to produce paper records of mundane high-school calculations or important engineering math. In the video, [Ready? Z80] explains the communication method with the aid of Hewlett-Packard’s own journal publication from October 1987, which lays out of the details of “the REDEYE Protocol.” Edgy stuff.

It’s pretty straightforward to understand, with the calculator sending out bursts of data in six to eight pulses at a time, modulated onto a 32.768 KHz square wave as is the norm. [Ready? Z80] then goes a step further, whipping up custom hardware to receive the signal and display the resulting data on a serial terminal. This is achieved with a TEC-1G single-board computer, based on the Z80 CPU, because that’s how [Ready? Z80] does things.

We’ve seen other great stuff from this channel before, too. For example, if you’ve ever wanted to multitask on the Z80, it’s entirely possible with the right techniques.

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BASIC On A Calculator Again

January 19, 2026 by Al Williams 7 Comments

We are always amused that we can run emulations or virtual copies of yesterday’s computers on our modern computers. In fact, there is so much power at your command now that you can run, say, a DOS emulator on a Windows virtual machine under Linux, even though the resulting DOS prompt would probably still perform better than an old 4.77 MHz PC. Remember when you could get calculators that ran BASIC? Well, [Calculator Clique] shows off BASIC running on a decidedly modern HP Prime calculator. The trick? It’s running under Python. Check it out in the video below.

Think about it. The HP Prime has an ARM processor inside. In addition to its normal programming system, it has Micropython as an option. So that’s one interpreter. Then PyBasic has a nice classic Basic interpreter that runs on Python. We’ve even ported it to one or two of the Hackaday Superconference badges.

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Graphing Calculator Gets USB-C Upgrade

January 7, 2026 by Bryan Cockfield 17 Comments

Unlike Texas Instruments, whose graphing calculators have famously not made technological improvements in decades despite keeping the same price tag, HP has made a few more modern graphing calculators in the last few years. One of which is the HP Prime which boasts hardware from the mid-2010s including an ARM processor, a color screen, and rechargeable lithium battery. But despite this updated hardware it’s still using micro-USB for data and charging. [David] wanted to fix that by giving this calculator a USB-C port.

The first steps were disassembling the calculator case and removing the micro-USB port. The PCB is glued to the LCD screen which isn’t ideal, but he was able to work on it with everything attached. The parts are small enough to need a microscope, and with a hot air station he was quickly able to remove the USB port. His replacements from a generic online retailer were able to be soldered without much effort, but there was one major complication. The new USB-C ports didn’t account for the “On The Go” mode supported by micro-USB and were shorting a pin to ground which put the calculator into “host” mode instead of acting as a device. But using the microscope and cutting a trace on the PCB disabled this mode permanently and got the calculator working properly.

As far as modernizing calculators go, it seems like the HP Prime checks a lot of boxes, with the major downside that the LCD screen and more powerful processor means that the battery needs to be charged more often than the old TI calculators. Rather than carry a dongle around everywhere, [David] found this to be a much more efficient change to his trusty HP. If you’re still stuck using TI calculators, though, there are a few ways to modernize those as well like this build which adds a lithium battery or this one which ports a few Game Boy games to the platform.