[lcamtuf] is not just a calculator superfan, but also a skilled builder. That much is evident in the fabulous design of Calcumator 2000, an electromechanical calculator that uses voltmeter readouts as digits (plus one at the bottom to represent decimal place). There are plenty of high-quality build images, so give it a look!
Meters like the one on the right (numbered 0 to 9) act as digit displays. The meter on the left indicates decimal position.
Calcumator 2000 is a bit of a love letter to a time when display technology hadn’t quite yet produced anything suitable for calculator use. This resulted in calculator designs that are generally unrecognizable compared to the 7-segment display based devices we see today. The Calcumator 2000, in all its electromechanical glory, would have fit right in that era.
The Calcumator 2000 has all the usual buttons one would expect from a simple calculator and drives a total of seven readouts, one of which acts as the decimal point. The idea of using voltmeters as digit displays came from [lcamtuf]’s voltmeter clock, an earlier work with a similar attention to detail in its design and assembly.
We want to take a moment to admire how clean the blue panel is. [lcamtuf] made it by painting one side of an acrylic panel, cutting the letters and design out on a CNC mill, then filling with white paint. The depth of the cuts gives the white elements a nifty multi-layer effect that really complements the design.
Want to see it work? Oh yes, you do. Check out the video, embedded just below.
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.
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!
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.
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.
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 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.
