A circular metal vessel is shown, with a symmetrical rotor of four vanes standing inside. At the bottom of the vessel are four loudspeakers.

Building An Acoustic Radiometer

November 22, 2025 by 1 Comment

A Crookes radiometer, despite what many explanations claim, does not work because of radiation pressure. When light strikes the vanes inside the near-vacuum chamber, it heats the vanes, which then impart some extra energy to gas molecules bouncing off of them, causing the vanes to be pushed in the opposite direction. On the other hand, however, it is possible to build a radiometer that spins because of radiation pressure differences, but it’s easier to use acoustic radiation than light.

[Ben Krasnow] built two sets of vanes out of laser-cut aluminium with sound-absorbing foam attached to one side, and mounted the vanes around a jewel bearing taken from an analog voltmeter. He positioned the rotor above four speakers in an acoustically well-sealed chamber, then played 130-decibel white noise on the speakers. The aluminium side of the vanes, which reflected more sound, experienced more pressure than the foam side, causing them to spin. [Ben] tested both sets of vanes, which had the foam mounted on opposite sides, and they spun in opposite directions, which suggests that the pressure difference really was causing them to spin, and not some acoustic streaming effect.

The process of creating such loud sounds burned out a number of speakers, so to prevent this, [Ben] monitored the temperature of a speaker coil at varying amounts of power. He realized that the resistance of the coil increased as it heated up, so by measuring its resistance, he could calculate the coil’s temperature and keep it from getting too hot. [Ben] also tested the radiometer’s performance when the chamber contained other gasses, including hydrogen, helium, carbon dioxide, and sulfur hexafluoride, but none worked as well as air did. It’s a bit counterintuitive that none of these widely-varying gasses worked better than air did, but it makes sense when one considers that speakers are designed to efficiently transfer energy to air.

It’s far from an efficient way to convert electrical power into motion, but we’ve also seen several engines powered by acoustic resonance. If you’d like to hear more about the original Crookes radiometers, [Ben]’s also explained those before.

RavynOS: Open Source MacOS With Same BSD Pedigree

November 22, 2025 by 6 Comments

That MacOS (formerly OS X) has BSD roots is a well-known fact, with its predecessor NeXTSTEP and its XNU kernel derived from 4.3BSD. Subsequent releases of OS X/MacOS then proceeded to happily copy more bits from 4.4BSD, FreeBSD and other BSDs.

In that respect the thing that makes MacOS unique compared to other BSDs is its user interface, which is what the open source ravynOS seeks to address. By taking FreeBSD as its core, and crafting a MacOS-like UI on top, it intends to provide the MacOS UI experience without locking the user into the Apple ecosystem.

Although FreeBSD already has the ability to use the same desktop environments as Linux, there are quite a few people who prefer the Apple UX. As noted in the project FAQ, one of the goals is also to become compatible with MacOS applications, while retaining support for FreeBSD applications and Linux via the FreeBSD binary compatibility layer.

If this sounds good to you, then it should be noted that ravynOS is still in pre-release, with the recently released ravynOS “Hyperpop Hyena” 0.6.1 available for download and your perusal. System requirements include UEFI boot, 4+ GB of RAM, x86_x64 CPU and either Intel or AMD graphics. Hardware driver support for the most part is that of current FreeBSD 14.x, which is generally pretty decent on x86 platforms, but your mileage may vary. For testing systems and VMs have a look at the supported device list, and developers are welcome to check out the GitHub page for the source.

Considering our own recent coverage of using FreeBSD as a desktop system, ravynOS provides an interesting counterpoint to simply copying over the desktop experience of Linux, and instead cozying up to its cousin MacOS. If this also means being able to run all MacOS games and applications, it could really propel FreeBSD into the desktop space from an unexpected corner.

Why Do We Love Weird Old Tech?

November 22, 2025 by 21 Comments

One of our newer writers, [Tyler August], recently wrote a love letter to plasma TV technology. Sitting between the ubiquitous LCD and the vanishing CRT, the plasma TV had its moment in the sun, but never became quite as popular as either of the other display techs, for all sorts of reasons. By all means, go read his article if you’re interested in the details. I’ll freely admit that it had me thinking that I needed a plasma TV.

I don’t, of course. But why do I, and probably a bunch of you out there, like old and/or odd tech? Take [Tyler]’s plasma fetish, for instance, or many people’s love for VFD or nixie tube displays. At Supercon, a number of people had hit up Apex Electronics, a local surplus store, and came away with some sweet old LED character displays. And I’ll admit to having two handfuls of these displays in my to-hack-on drawer that I bought surplus a decade ago because they’re so cute.

It’s not nostalgia. [Tyler] never had a plasma growing up, and those LED displays were already obsolete before the gang of folks who had bought them were even born. And it’s not simply that it’s old junk – the objects of our desire were mostly all reasonably fancy tech back in their day. And I think that’s part of the key.

My theory is that, as time and tech progresses, we see these truly amazing new developments become commonplace, and get forgotten by virtue of their ever-presence. For a while, having a glowing character display in your car stereo would have been truly futuristic, and then when the VFD went mainstream, it kind of faded into our ambient technological background noise. But now that we all have high-res entertainment consoles in our cars, which are frankly basically just a cheap tablet computer (see what I did there?), the VFD becomes an object of wonder again because it’s rare.

Which is not to say that LCD displays are anything short of amazing. Count up the rows and columns of pixels, and multiply by three for RGB, and that’s how many nanoscale ITO traces there are on the screen of even the cheapest display these days. But we take it for granted because we are surrounded by cheap screens.

I think we like older, odder tech because we see it more easily for the wonder that it is because it’s no longer commonplace. But that doesn’t mean that our current “boring” tech is any less impressive. Maybe the moral of the story is to try to approach and appreciate what we’ve got now with new eyes. Pretend you’re coming in from the future and finding this “old” gear. Maybe try to figure out how it must have worked.

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A small, colorful synth built for a 3-year-old. It has five pots, four sliders, and a tiny screen.

Baby’s First Synth Was Daddy’s First Project

November 22, 2025 by 3 Comments

We absolutely adore inspired labor-of-love tales such as this one. [Alastair] wanted to build a synth for his daughter’s third birthday in spite of having no prior hardware knowledge. It became the perfect excuse to learn about CAD, microcontrollers, PCB design, and of course, 3D printing.

So, why a synth for a toddler? Aside from plain old ‘why not?’, the story goes that she received a Montessori busy-type board which she seemed to enjoy, and it reminded [Alastair] of the control surface of a synth. He wondered how hard it could be to build something similar that made sound and didn’t require constant button presses.

[Alastair] began his journey by dusting off a 15-year-old Arduino Inventors Kit. The initial goal was to get potentiometer readings and map them to 12 discrete values, and then emit MIDI messages. This was easy enough, and it was time to move to a synth module and an Elegoo Nano.

The full adventure is definitely worth the read. Be sure to check out the pink version in action after the break. You really don’t wanna miss the lil’ panda bear. Trust us.

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It’s Hard To Make A (Good) Oscillator

November 22, 2025 by 12 Comments

There’s more to making an oscillator than meets the eye, and [lcamtuf] is here with a good primer on the subject. It starts with the old joke that if you need an oscillator it’s best to try to make an amplifier instead, but of course the real point here is to learn how to make not just a mere oscillator, but a good oscillator.

He does this by taking the oscillator back to first principles and explaining positive feedback on an amplifier, before introducing the Schmitt trigger, an RC circuit to induce a delay, and then phase shift. These oscillators are not complex circuits by any means, so understanding their principles should allow you to unlock the secrets of oscillation in a less haphazard way than just plugging in values and hoping.

Oscillation is a subject we’ve taken a deep dive into ourselves here at Hackaday, should you wish to learn any more. Meanshile [lcamtuf] is someone we’ve heard from here before, with a comparative review of inexpensive printed circuit board manufacturers.

Microsoft Open Sources Zork I, II And III

November 21, 2025 by 13 Comments

The history of the game Zork is a long and winding one, starting with MUDs and kin on university mainframes – where students entertained themselves in between their studies – and ending with the game being ported to home computers. These being pathetically undersized compared to even a PDP-10 meant that Zork got put to the axe, producing Zork I through III. Originally distributed by Infocom, eventually the process of Microsoft gobbling up game distributors and studios alike meant that Microsoft came to hold the license to these games. Games which are now open source as explained on the Microsoft Open Source blog.

Although the source had found its way onto the Internet previously, it’s now officially distributed under the MIT license, along with accompanying developer documentation. The source code for the three games can be found on GitHub, in separate repositories for Zork I, Zork II and Zork III.

We previously covered Zork’s journey from large systems to home computers, which was helped immensely by the Z-machine platform that the game’s code was ported to. Sadly the original games’s MDL code was a bit much for 8-bit home computers. Regardless of whether you prefer the original PDP-10 or the Z-machine version on a home computer system, both versions are now open sourced, which is a marvelous thing indeed.

How To Use That Slide Rule

November 21, 2025 by 16 Comments

You have that slide rule in the back of the closet. Maybe it was from your college days. Maybe it was your Dad’s. Honestly. Do you know how to use it? Really? All the scales? That’s what we thought. [Amen Zwa, Esq.] not only tells you how slide rules came about, but also how to use many of the common scales. You can also see his collection and notes on being a casual slide rule collector and even a few maintenance tips.

The idea behind these computing devices is devilishly simple. It is well known that you can reduce a multiplication operation to addition if you have a table of logarithms. You simply take the log of both operands and add them. Then you do a reverse lookup in the table to get the answer.

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