You’ve likely seen an X-cube, a dichoric prism used to split light into its constituent colours–you know, those fun little cubes you get when tearing apart a broken projector. Have you considered that the X-cube need not be a cube for its entire existence? [Matt] at “Matt’s Corner of Gem Cutting” on YouTube absolutely did, which is why he ground one into a 216-facet disco ball.

That’s the hack, really. He took something many of us have played with at our desks thinking “I should do something cool with this” and… did something cool with it that most of us lack the tools and especially skills to even consider. It’s not especially practical, but it is especially pretty. Art, in other words.

The shape he’s using is known specifically to gemologists as “Santa’s Little Helper II” though we’d probably describe it as a kind of isosphere. Faceting the cube is just a matter of grinding down the facets to create the isosphere, then polishing them to brilliance with increasingly finer grit. This is done one hemisphere at a time, so the other hemisphere can be safely held in place with the now-classic cyanoacrylate and baking soda composite. Yes, jewelers use that trick, too.

We were slightly worried when [Matt] dumped his finished disco ball in acetone to clean off the cyanoacrylate– we haven’t the foggiest idea what optical-quality glue is used to hold the four prisms of an X-cube together and were a little worried acetone might soften the joints. That turned out not to be an issue, and [Matt] now has the most eye-catching sun-catcher we think we’ve ever seen.

We actually have seen suncatchers before, though admittedly it’s not a very popular tag around here. The closest build to this one was a so-called “hypercrystal” that combined an infinitiy mirror with a crystaline shape and dicloric tape for an effect as trippy as it sounds.

We also featured a deep-dive a while back if you want to know how these colourful, hard-to-pronounce coatings work.

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If you wanted to build a robot that chased light, you might start thinking about Raspberry Pis, cameras, and off-the-shelf computer vision systems. However, it needn’t be so complex. [Ed] of [Death and the Penguin] demonstrates this ably with a simple robot that finds the light the old-fashioned way.

The build is not dissimilar from many line-following and line chasing robots that graced the pages of electronics magazines 50 years ago or more. The basic circuit relies on a pair of light-dependent resistors (LDR), which are wrapped in cardboard tubes to effectively make their response highly directional. An op-amp is used to compare the resistance of each LDR. It then crudely steers the robot towards the brighter light between turning one motor hard on or the other, operating in a skid-steer style arrangement.

[Ed] then proceeded to improve the design further with the addition of a 555 timer IC. It’s set up to enable PWM-like control, allowing one motor to run at a lower speed than the other depending on the ratio between the light sensors. This provides much smoother steering than the hard-on, hard-off control of the simpler circuit. [Ed] notes that this is about the point where he would typically reach for a microcontroller if he hoped to add any additional sophistication.

In an era where microcontrollers seem to be the solution to everything, it’s nice to remember that sometimes you can complete a project without using a processor or any code at all. Video after the break.

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In a recent video [QWZ Labs] demonstrates an interesting technique to use 3D printing to make creating custom PCBs rather straightforward even if all you have is a 3D printer and a roll of copper tape.

The PCB itself is designed as usual in KiCad or equivalent EDA program, after which it is exported as a 3D model. This model is then loaded into a CAD program – here Autodesk Fusion – which is used to extrude the traces by 0.6 mm before passing the resulting model to the 3D printer’s slicer.

By extruding the traces, you can subsequently put copper tape onto the printed PCB and use a cutting tool of your choice to trace these raised lines. After removing the rest of the copper foil, you are left with copper traces that you can poke holes in for the components and subsequently solder onto.

As far as compromises go, these are obviously single-sided boards, but you could probably extend this technique to make double-sided ones if you’re feeling adventurous. In the EDA you want to use fairly thick, 2 mm trace width with plenty of clearance to make your copper cutting easy, while in the slicer you have to check that the traces get printed properly. Using the Arachne wall generator option for example helps to fill in unpleasant voids, and the through-holes ought to be about 1 mm at least lest the slicer decides that you really want to drill them out later by hand instead.

While soldering is pretty easy on copper tape like this, desoldering would be more challenging, especially with hot air. In the video PLA was used for the PCB, which of course is rather flexible and both softens and melts easily when exposed to heat, neither of which make it look very good compared to FR4 or even FR1 PCB materials. Of course, you are free to experiment with whatever FDM, SLA or even SLS materials you fancy that would work better for the board in question.

Although obviously not a one-size-fits-all solution for custom PCBs, it definitely looks a lot easier than suffering through the much-maligned prototype perfboards that do not fit half the components and make routing traces hell. Now all we need is the ability to use e.g. targeted vapor-deposition of copper to make fully 3D printed PCBs and this method becomes even easier.

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This week Jonathan chats with Toke Hoiland-Jorgensen about CAKE_MQ, the newest Kernel innovation to combat Bufferbloat! What was the realization that made CAKE parallelization? When can we expect it in the wild? And what’s new in the rest of the kernel world? Watch to find out!

• Blog: blog.tohojo.dk/feed/
• Github: github.com/tohojo
• Mastodon: @

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Did you know you can watch the live recording of the show right on our YouTube Channel? Have someone you’d like us to interview? Let us know, or have the guest contact us! Take a look at the schedule here.

play.libsyn.com/embed/episode/…

Direct Download in DRM-free MP3.

If you’d rather read along, here’s the transcript for this week’s episode.

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Theme music: “Newer Wave” Kevin MacLeod (incompetech.com)

Licensed under Creative Commons: By Attribution 4.0 License

hackaday.com/2026/01/28/floss-…

If you’re an old-schooler, you might still go to the local bar and pay for a beer with cash. You could even try and pay with a cheque, though the pen-and-paper method has mostly fallen out of favor these days. But if you’re a little more modern, you might use a tap-to-pay feature on a credit or debit card.

In Taiwan, though, there’s another unique way to pay. The island nation has a whole ecosystem of bespoke payment cards, and you can even get one that looks like a floppy disk!

It’s Not About The Money, Money, Money

A regular adult iPASS card. Like many mass transit smartcards, it’s based on MIFARE contactless technology. Credit: iPASS
Like so many other countries with highly-developed public transport systems, Taiwan implemented a smartcard ticketing system many years ago. Back in December 2007, it launched iPASS (一卡通), initially for use by riders on the Kaohsiung Metro system which opened in March 2008. The cards were launched using MIFARE technology, as seen in a wide range of contactless smart card systems in other public transport networks around the world.

The system was only ever supposed to be used to pay fares on public transport using the pre-paid balance on the card. Come 2014, however, management of the cards was passed to the iPASS Corporation. The new organization quickly established the card’s use as a widespread form of payment at a huge variety of stores across Taiwan. The earliest adopters were OK MART, SUNFAR 3C, and a handful of malls and department stores. Soon enough, partnerships with FamilyMart and Hi-Life convenience stores followed, and the use of the card quickly spread from there.
iPASS can be used across much of the public transport in Taiwan, and the cards are also compatible with smartphone wallets. Credit: iPASS
As iPASS cards continued to gain in popularity, companies started lining up to produce co-branded cards. Many came with special deals at select retailers. For example, NPC issued an iPASS card that offered cheaper prices on gasoline at affiliated gas stations. Furthermore, no longer did your iPASS have to be a rigid, rectangular plastic card. You can buy a normal one if you like, but you can also get an iPASS built into prayer beads, laced into a leather bracelet, or even baked into a faux floppy disk. The latter specifically notes that it’s not a real disk, of course; it only has iPASS functionality and will not work if you put it in a floppy drive. It is, however, a startlingly good recreation, with the proper holes cut out for write protect and density and a real metal sheath. On the translucent yellow version, you can even see what appears to be the fabric inside that would be used to protect the spinning magnetic platter.
Novelty iPass cards are common. Some are merely fun prints or designs, while others go far outside the usual smartcard format—like this novelty floppy disk. Credit: iPASS
Other novelty iPASS “cards” include a keychain-sized Taiwan Railways train and a Japanese shinkansen. Where a regular iPASS card costs NT$100 or so, a novelty version like the floppy disk or train costs more like NT$500-$600. That might sound like a lot, but in the latter case, you’re only talking about $15 USD or so. If so desired, though, you don’t need to carry a card or keychain, or floppy disk at all. It’s possible to use an iPASS with contactless smartphone and smartwatch wallets like Google Wallet and Garmin Pay.

iPASS Cards are typically sold empty with no value, and must have money transferred to the card prior to use. Notably, the money stored on the cards is backed by the Union Bank of Taiwan. This provides a certain level of peace of mind. Even if it wasn’t there, though, there isn’t so much to lose if things do go wrong—as any individual card is limited to storing a maximum of NT$10,000 (~$320 USD).
You can use a little train as your iPASS card if you’re willing to spend just a little more money. Credit: PCHOME.TW
Similar Taiwanese pre-paid payment cards exist, too. EasyCard has been around since 2002, initially established by the Taipei Smart Card Corporation for use on the Taipei Metro. It similarly offers novelty versions of its cards, and these days, it can be used on most public transport in Taiwan and at a range of convenience stores. Like the iPASS, it’s limited to storing up to NT$10,000, with balances backed by the Cathay United Bank. 7-Eleven has also joined the fray with its iCash cards, which are available in some very cute novelty styles. However, where there are tens of millions of users across EasyCard and iPASS, iCash has not had the same level of market penetration.
As Easycard demonstrates, you can put a contactless payment chip in just about anything. Credit: PCHOME.TW
Generally, most of us get by using payment cards linked directly to our main banking accounts. However, if you happen to find yourself in Taiwan, you might find the iPASS to be a very useful tool indeed. You can load it once with a bunch of money, and then run around on buses and trains while buying yourself snacks and beverages all over town. Plus, if you buy the floppy disk one, you’ll have an awesome souvenir to bring back with you, and you can entertain all your payment-card-obsessed friends with tales of your adventures. All in all, the banking heavyweights of the world would do well to learn from the whimsical example of the iPASS Corporation.

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We know that while the cost per byte of persistent storage has dropped hugely over the years, it’s still a pain to fork out for a new disk drive. This must be why [MadAvidCoder] has taken a different approach to storage, placing files as multiple encoded pieces of metadata in Wikipedia edits.

The project takes a file, compresses it, and spits out small innocuous strings. These are placed in the comments for Wikipedia edits — which they are at pains to stress — were all legitimate edits in the test cases. The strings can then be retrieved at will and reconstituted, for later use. The test files are a small bitmap of a banana, and a short audio file.

It’s an interesting technique, though fortunately one that’s unlikely to be practical beyond a little amusement at the encyclopedia’s expense. We probably all have our favorite examples of low quality Wikipedia content, so perhaps it’s fortunate that these are hidden in the edit history rather than the pages themselves. Meanwhile we’re reminded of the equally impractical PingFS, using network pings as a file system medium.

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While it has become a word, laser used to be an acronym: “light amplification by stimulated emission of radiation”. But there is an even older technology called a maser, which is the same acronym but with light switched out for microwaves. If you’ve never heard of masers, you might be tempted to dismiss them as early proto-lasers that are obsolete. But you’d be wrong! Masers keep showing up in places you’d never expect: radio telescopes, atomic clocks, deep-space tracking, and even some bleeding-edge quantum experiments. And depending on how a few materials and microwave engineering problems shake out, masers might be headed for a second golden age.

Simplistically, the maser is — in one sense — a “lower frequency laser.” Just like a laser, stimulated emission is what makes it work. You prepare a bunch of atoms or molecules in an excited energy state (a population inversion), and then a passing photon of the right frequency triggers them to drop to a lower state while emitting a second photon that matches the first with the same frequency, phase, and direction. Do that in a resonant cavity and you’ve got gain, coherence, and a remarkably clean signal.

The Same but Different

Townes with his original maser (public domain).
However, there are many engineering challenges to building a maser. For one thing, cavities are bigger than required for lasers. Sources of noise and the mitigations are different, too.

The maser grew out of radar research in the early 1950s. Charles Townes and others at Columbia University used ammonia in a cavity to produce a 24 GHz maser, completing it in 1953. For his work, he would share the 1964 Nobel Prize for physics with two Soviet physicists, Nikolay Basov and Alexander Prokhorov, who had also built a maser.

Eclipsed but Useful

By 1960, the laser appeared, and the maser was nearly forgotten. After all, a visible-light laser is something anyone can immediately appreciate, and it has many spectacular applications.

At the time, the naming of maser vs laser was somewhat controversial. Townes wanted to recast the “M” in maser to mean “molecular,” and pushed to call lasers “optical masers.” But competitors wanted unique names for each type of emission, so lasers for light, grasers for gamma rays, xasers for X-rays, and so on. In the end, only maser and laser stuck.

Masers have uses beyond fancy physics experiments. Trying to detect signals that are just above the noise floor? Try a cryogenic maser amplifier. That’s one way the NASA Deep Space Network pulls in signals. (PDF) You cool a ruby, or other material, to just a bit of 4 °K and use the output of the resulting maser to pull out signals without adding much noise. This works well for radio astronomy, too.

Need an accurate time base? Over the long term, a cesium clock is the way to go. But over a short period, a hydrogen maser clock will offer less noise and drift. This is also important to radio astronomy for building systems to use very long baseline interferometry. The NASA network also uses masers as a frequency standard.

All Natural

While we didn’t have our own masers until 1953, nature forms them in space. Water, hydroxyl, and silicon monoxide molecules in space can form natural masers. Scientists can use these astrophysical masers to map regions of space and measure velocities using Doppler shifts.

Harold Weaver found these in 1965 and, as you might expect, they operate without cavities, but still emit microwaves and are an important source of data for scientists studying space.

Future

While traditional masers are difficult to build, modern material science may be setting the stage for a maser comeback. For example, using nitrogen-vacancy centers in diamonds rather than rubies can lead to masers that don’t require cryogenic cooling. A room-temperature maser could open up applications in much the same way that laser diodes made things possible that would not have been practical with high-voltage tubes and special gases.

Masers can produce signals that may be useful in quantum computing, too. So while you might think of the maser as a historical oddity, it is still around and still has an important job to do.

In a world where lasers are so cheap that they are a dollar-store cat toy, we’d love to see a cheap “maser on a chip” that works at room temperature might even put the maser in reach of us hackers. We hope we get there.

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Home automation with high usefulness and low annoyance tends to rely on reliable person sensing, and [francescopace]’s ESPectre shows one way to do that cheaply and easily by leveraging hardware that’s already present on a common dev board.

ESPectre is an ESP32-based open source motion detector that detects movement without any cameras or microphones. It works similarly to millimeter-wave (mmWave) radar motion detectors in the sense that when a person moves, wireless signals are altered slightly as a result. ESPectre can detect this disturbance by watching and analyzing the Wi-Fi channel state information (CSI) and doing some very smart math and filtering. It’s cheap, easy to deploy and use, and even integrates with Home Assistant.

Combining a sensor like this with something else like a passive infrared (PIR) motion sensor is one way to get really robust results. But keep in mind that PIR only senses what it can see, whereas ESPectre works on WiFi, which can penetrate walls.

Since ESPectre supports low-cost ESP32 variants and is so simple to get up and running, it might be worth your time to give it a trial run. There’s even a browser-based ghost-dodging game [francescopace] put online that uses an ESPectre board plugged in over USB, which seems like a fun way to get a feel for what it can do.

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If your travels take you near Mountain View, California, you can have the pleasure of visiting the Computer History Museum. You can see everything from a PDP-1 to an Altair 8800 to a modern PC there. If you aren’t travelling, the museum has launched a digital portal that expands your ability to enjoy its collection remotely.

CEO Marc Etkind said, “OpenCHM is designed to inspire discovery, spark curiosity, and make the stories of the digital age more accessible to everyone, everywhere. We’re unlocking the collection for new audiences to explore.”

The portal features advanced search tools along with browsable curated collections and stories. There’s also an album feature so you can create and share your own custom collections. If you are a developer, the portal also allows access via an API.

As an example, we checked out the vintage marketing collection. Inside were a 1955 brochure for a Bendix computer you could lease for under $1,000 a month, and a 1969 brochure for the high-performance Hitachi HITEC 10. It had 4K words of 16-bit memory and a clock just a bit more than 700 kHz, among others.

If you are on the other side of the Atlantic, you might want to check out a very large museum there. There’s also a fine museum in the UK.

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Decades ago, shows like Star Trek, The Jetsons, and Lost in Space promised us a future full of helpful computers and robot assistants. Unfortunately, we haven’t quite gotten our general-purpose helper to do all of our tasks with a simple voice command yet. But if some sweat equity is applied, we can get machines to do specific tasks for us under some situations. [Max Maker] built this remote-controlled lawnmower which at least minimizes the physical labor he needs to do to cut his grass.

The first step in the project was to remove the human interface parts of the push mower and start working on a frame for the various control mechanisms. This includes adding an actuator to raise and lower the mower deck on the fly. Driving the new rear wheels are two wheelchair motors, which allow it to use differential steering, with a set of casters up front for maximum maneuverability. An Arduino Mega sits in a custom enclosure to control everything and receive the RC signals, alongside the mower’s batteries and the motor controllers for the drive wheels.

After some issues with programming, [Max] has an effective remote controlled mower that he can use to mulch leaves or cut grass without getting out of his chair. It would also make an excellent platform if he decides to fully automate it in the future, which is a project that has been done fairly effectively in the past even at much larger scales.

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