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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LiDAR Matrix Sensor Sees In 3D

May 14, 2026 by Al Williams 6 Comments

[Mellow_Labs] picked up a few LiDAR matrix sensors and found them very exciting. While a normal time-of-flight sensor can accurately determine a range, the matrix sensor is like an array of 64 sensors that can build a 2D map of distances from 2 cm to 3.5 m. [Mellow] wanted to add the sensor to his robot to help it see what was in front of it. You can see how it worked out in the video below.

The robot in question is Zippy, a 3D printed tank-like robot with an ESP32. By default, the robot requires control inputs, but using the sensor will enable autonomous operation. For good or ill, the sensor mounted to Zippy was seeing the floor with about half of the rows. That means about 50% of the data went to waste. However, we think having a robot be able to see the floor in front of it might be a good thing.

[Mellow] used an LLM to write most of the code, so there were a number of iterations required to get things working. This required decimating even more of the data from the sensor. Still, pretty impressive.

Want to learn more about ToF sensors? Or if you want to focus on the practical, there’s code you can borrow.

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How Did Apollo Separate?

May 13, 2026 by Al Williams 23 Comments

If you’ve watched a Saturn V launch, you’ve probably seen how a large rocket will often jettison a stage on the way up. There are several reasons for this — there is no reason to haul an empty fuel container, for example. However, you can probably imagine how the separation works. You release something — probably explosive bolts — and gravity pulls the old stage away from you as you climb on the next stage’s engines. But what about on the way back? The command module drops the service module before reentry. [Apollo11Space] has a video explaining just how complicated that was to pull off. You can watch it below.

The main problem? The service module has almost everything you need: oxygen, a big engine, fuel, and electrical generation capability. If you’ve ever seen a real command module, they are tiny. Somehow, you need to get the command module prepared to be on its own for the amount of time it takes to land, and get the service module safely away.

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Measure The Earth’s Rotation Victorian Style

May 13, 2026 by Al Williams 8 Comments

You’ve probably seen a Foucault pendulum in a museum. This Victorian-era science demonstration is named after physicist Léon Foucault and shows how the Earth rotates compared to a pendulum moving in a fixed plane. [RyanCreates] shows you how you can make your own, and it is surprisingly simple.

All you need is a heavy weight like a small mushroom anchor, fishing line, and a swivel — all things you can pick up at any sporting goods store. You’ll need a way to suspend it all, such as an eye hook in the ceiling.

In addition to the mechanical parts, the build calls for a camera to record the results and a lighter or other source of flame. The reason? To release the pendulum, you burn a thread that prevents it from swinging. This allows for a clean release with no sideways force.

The amount of your rotation depends on your latitude. At 33 degrees north, for example, you can expect 360*sin(33)/24 or 8.17 degrees per hour of rotation. [Ryan] measured a somewhat larger number, which was probably due to an error source, especially since he is measuring the angle using captured camera frames in Photoshop. That has to introduce some error, and small pendulums like this are incredibly sensitive to errors.

If you try it and find the source of the error, we’re sure [Ryan] would love to hear from you. Museum pieces are typically much larger, have ultra-low-friction pivots, and use electromagnets to keep the pendulum moving since, after all, even a Foucault pendulum can’t run forever.

The Truth About The Hindenburg

May 12, 2026 by Al Williams 27 Comments

The Hindenburg disaster recently marked its 89th anniversary, and [The History Guy] marked the event with a video that dispels many of the myths surrounding the airship. Example: the disaster did not actually occur on the airship’s maiden voyage. That isn’t true. The ship was on its 63rd voyage. However, it was the first flight of the 1937 season.

The giant ship burned because of the hydrogen gas inside, but the cause of the fire remains debatable and was likely not solely due to hydrogen. In fact, from a technical standpoint, the ship didn’t explode. It only burned.

Some of the myths are just from sloppy reporting or the tendency of people to misunderstand things. Others are a blurring in the common consciousness of the Hindenburg and the Titanic.

It is easy to think of the necessity for safe engineering when you are building, say, a bomb or a spacecraft. But anything capable of wreaking havoc requires careful design and testing. However, ships like the Hindenburg had made many trips without incident. Sure, the Hindenburg was a spectacle, but even the fatality rate was fairly low. Many of those who died jumped to the ground — they might have survived if they had waited a minute.

There are many myths around [Herb Morrison]’s famous “Oh the humanity!” report. We’ve noted before that it was played back at the wrong speed for decades. Airships have a stranger history than you might imagine.

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The History Of Altec Lansing

May 12, 2026 by Al Williams 21 Comments

If you bought computer audio hardware a few decades ago, you may remember coming across products from Altec Lansing. That you probably haven’t thought of that name in some time doesn’t surprise us, the company has not fared well in recent years and has changed hands multiple times. [The Last Shift] tells the company’s history in a video you can watch below.

James Lansing started Lansing Manufacturing, offering high-end speakers for the fledgling “talkie” movie industry. It had some success, but the depression put them on shaky footing. Meanwhile, a company named All Technical Service Company, or Altec, was a large organization that serviced Western Electric movie theater equipment. Flush with cash, they merged with Lansing Manufacturing to form Altec Lansing. With a large infrastructure and Lansing’s engineering, they became a significant supplier to the military during World War II.

After the war, the company produced a landmark theater speaker system that became the gold standard in theater audio. However, Lansing didn’t like the big company environment and left to found a company that bore his full name, James B. Lansing, which you may know as JBL.

Altec Lansing continued to grow. However, a series of mergers and sales starting in 1969 caused the Altec Lansing company to decline. By the 1990s, Altec Lansing was making cheap PC speakers. A far cry from the gold-standard massive speakers made by the company during its heyday.

We love the history of technology and the people that drove them. Bing Crosby, for example. Or the lesser-known heroes like Edwin Armstrong.

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The Walls Don’t Have Ears, But Fiber Optic Does

May 11, 2026 by Al Williams 12 Comments

You normally think of fiber optic as something used in network cables. However, scientists employ dedicated fibers to detect earthquakes. In simple terms, they fire a laser down the fiber and watch reflections caused by imperfections. When vibrations hit the cable, it changes the defects, which show up in the return pattern. However, with the right techniques, those vibrations could just as easily be from people speaking near the cable.

If you are alarmed, there’s good news and bad news. The good news is that the technique seems to be limited to coils of fiber that are not buried, and you have to be within about 5 meters of the fiber. The bad news is that there is plenty of dark cable all over the place. Besides, if researchers can do this successfully, you would imagine three-letter agencies around the world could do it even better.

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