Mysterious Files PH

Ultrasonic levitation is by now a familiar trick: one or more ultrasonic transducers create a standing wave, and small objects can be held in the nodes of this standing wave. With a sufficiently large array of transducers, it’s even possible to control the movement of the object. This isn’t the only form of ultrasonic levitation, however, as [Steve Mould] demonstrated with his ultrasonic air hockey table.

This less familiar form of levitation was discovered by [Bob Collins] while working on torpedo guidance systems: when he tried to place a glass lens on an ultrasonic transducer it immediately slid off. He found during further experimentation that an ultrasonic transducer would levitate over any sufficiently flat and smooth surface. It works by trapping a very thin layer of air between the transducer and the smooth surface. When the transducer moves sharply toward the surface, it compresses a layer of air in between, and forces some air out, and the reverse happens while pulling back. However, during the downstroke, the gap through which air can escape is narrower than during the upstroke, and there is more surface-induced drag, meaning that the inflow and outflow of air through a narrow gap isn’t completely equal. At a certain distance, inflow and outflow balance, and the transducer floats on a thin layer of air.

In [Steve]’s air hockey arena, the floor oscillates and the pucks levitate over this. Driving it using just one transducer didn’t work, since the floor formed standing waves, and the pucks would get stuck on node lines. Instead, he used two transducers, one at each end of the arena, and drove them out of phase with each other. This created a standing wave and minimized dead spots.

The arena was a bit small (having to be played using toothpicks), but it seemed to work well. If you prefer your air hockey a bit more human-scaled, we’ve seen a table build before. We’ve also seen ultrasonic levitation before, ranging from simple electronics kits to the driving force behind a full volumetric display or photography station.

Springs are great, but making them out of plastic tends to come with some downsides, for fairly obvious reasons. Creating a compliant mechanism that can be 3D printed and yet which doesn’t permanently deform or wear out after a few uses is therefore a bit of a struggle. The complaint toggle mechanism that [neotoy] designed is said to have addressed those issues, with the model available on Printables for anyone to give a shake.

The model in question is a toggle, which is the commonly seen plastic or metal device that clamps down on e.g. rope or cord and requires you to push on it to have it release said clamping force. Normally these use a metal spring inside, but this version is fully 3D printable and thus forms a practical way to test this particular compliant mechanism with a variety of materials.

The internal spring is a printed spiral spring, with the example in the video printed in PETG. You can of course also print it in other materials for different durability and springiness properties. As noted in the video, PLA makes for a very poor spring material, so you probably want to skip that one.

We covered compliant mechanisms in the past for purposes like blasters, including some that you can only see under a microscope.

When building a project to operate on battery power for long periods of time, having a microcontroller with a reliable and extremely low-power sleep mode is critical. When processing power isn’t needed, it should be able to wait around using almost no energy until an interrupt triggers it. Once triggered, the CPU performs its tasks and then puts itself right back to sleep, making sure the battery lasts as long as possible. Unfortunately, not every microcontroller has sleep capabilities or has an acceptably low level of power use for maximizing battery life. For these systems, a tool like this power manager might come in handy.

The small PCB, called the powerTimer, essentially acts as a middleman for power delivery to another microcontroller. On the PCB is an RV3028-C7 real-time clock, which uses a mere 45 nA of current and can interact with the second microcontroller through a timer or alarm. When commanded, the powerTimer uses an SR latch as its main control circuit, allowing single button presses to change the power state for the second microcontroller. Once the powerTimer powers up the second microcontroller, that microcontroller can communicate back to the powerTimer with a “DONE” signal, and once this signal is received, the powerTimer will cut power and wait for the next interrupt to occur.

The project’s creator, [Juan], had this idea for an ESP32 with a camera module.  While it does have a sleep mode, the ESP32 wasn’t nearly low-power enough to get the battery life that he wanted. With a modular system like this, it can be used in many other applications as well. PowerTimer is one of the entries in our 2026 Green Powered Challenge.

[Shreeyash] asks an interesting question: how many registers does your CPU have? The answer is probably more than you think. The reason? Modern CPUs — at least many of them — execute instructions out of sequence so they can perform multiple instructions per clock cycle. To do this, they may need to execute instructions that change registers that other instructions are still reading. In addition, you might be writing a result speculatively — a branch might make it where your result won’t wind up in the target register. The answer to both of these problems is register renaming.

The ARM CPU he looks at has many physical registers you can’t see. These get mapped to the registers you use on the fly. So when you read a register in software, you are really getting an underlying physical register. Which one? Depends on when you read it.

The RAT, or Register Alias Table, keeps track of the mapping between physical registers and the register names you use. Not only does this allow the CPU to run operations out of order, but it also lets results sit in unnamed physical registers until the time is right for it to become the real register. As a byproduct, moving one register to another becomes fast since you can just copy the alias of one physical register to another logical register.

Not clear? Try reading the post. There are other ways to get the same result (e.g., reservation stations), but the technique goes way back to mainframe computers. While it didn’t appear right away in microprocessors, modern ones often execute out of order and have to have some scheme to address this problem.

If you build your own CPUs with FPGAs, it is possible to do the same trick. There are also RISC-V variants that can do it.

It’s been three weeks since the Artemis II crew returned to Earth, and while the mission might be over for Reid Wiseman, Victor Glover, Christina Hammock Koch, and Jeremy Hansen, the work is only just beginning for engineers back at NASA. In a blog post earlier this week, the space agency went over the preliminary post-mission assessments of the spacecraft and its ground support equipment, and detailed some of the work that’s currently taking place as preparations begin for Artemis III.

During Artemis I, higher than expected damage was noted on both the Orion’s heat shield and the Space Launch System (SLS) launch pad. But according to NASA, the changes implemented after that first mission seem to have prevented similar issues this time around. The post also explains that reusable components of the Orion spacecraft, such as the avionics and the crew seats, are already in the process of being removed from Integrity so they can be installed in the next capsule on the production line.

While watching the live stream of the Artemis mission is the closest most of us will ever get to experiencing spaceflight, that doesn’t mean you can’t explore the solar system from the comfort of your own home — or more specifically, your browser. [Sani Huttunen] has created an incredible web-based solar system simulator that lets you explore our celestial neighborhood throughout different periods of time. You can tour the moons of Jupiter, see how the planets aligned on the date of your birth, and even check in on the Voyager probes. There are some very valid reasons to be skeptical about software moving to the web, but we’ve got to admit, this is a very slick demonstration of just how far modern browsers have come.

Speaking of how far things have come, are you ready for a car without a rear window? Polestar certainly hopes so, as their latest model does away with such quaint concepts. The glass panel in the roof ends right around the back headrests, and while the rear of the vehicle does open up for storage, the hatch is completely solid. In place of the traditional mirror, there’s a “high resolution” 1480 x 320 display that shows the feed from a rear-mounted camera.

No, that’s not a typo. At a time when smartphones are shipping with 2K displays, should the driver want to see what’s going on behind their $70,000+ USD electric vehicle, they’re limited to seeing it at a vertical resolution below that of VGA. We’d make a joke about Polestar offering up a “Rearview+” upgrade down the line that would give the driver a higher resolution view, but honestly, it’s getting a little too close to reality to be funny.

If that last one has you wishing for a reminder of simpler times, how about some new software for using the iconic Wii Remote as an input device? The Wii and its revolutionary controllers may be turning 20 later this year, but that hasn’t stopped the dedicated fans. This new wrapper provides accelerometer calibration, infrared tracking, and the ability to remap the Wii Remote’s buttons and create key combos. If you do something cool with it, we’d love to hear about it.

Finally, on the other end of the input spectrum, some details leaked out this weekend about Valve’s upcoming Steam controller — namely, the fact that it will cost players $99 at release. As reported by VICE, a hands-on review of the controller by TechyTalk was accidentally published early on YouTube, providing the public with pricing info ahead of an official announcement.

At first blush, this might seem like a lot of money to pay for a game controller, but it’s actually within striking distance of the sticker price on the standard controllers on the Xbox and PlayStation consoles. Perhaps more critically, it’s around half the price of the official “premium” controller offerings available for the aforementioned systems. Is it really any wonder that we’ve got cars without rearview mirrors when folks are putting down 200 bucks for a fancy PlayStation controller?

See something interesting that you think would be a good fit for our weekly Links column? Drop us a line, we’d love to hear about it.

For those first venturing into sailing, it can be overwhelming since the experience is thick with jargon and skills that don’t often show up in life ashore. With endless choices, including monohulls versus catamarans, fiberglass versus wood, fractional versus masthead rigs, and sloops versus ketches, a new sailor risks doing something like single-handing a staysail schooner when they should have started on a Bermuda-rigged dinghy without a spinnaker. Luckily, there are some shortcuts to picking up the hobby, like the venerable Sunfish or Hobie ships. It’s also possible to build a simple sailing vessel completely out of materials from a local hardware store, as [Cumberland Rover] has been demonstrating.

[Cumberland Rover] has a number of homemade vessels under his belt, from various kayaks and rowboats. His latest project is a 12-foot rowboat, which has the option to add a mast and sail. The hull is made from two 1×12 pieces of lumber, bent around a frame and secured. Plywood makes the bottom, and a few seats finish out the build. He’s also using standard hardware to fasten everything together, which helps with maintenance. It came in handy when he recently added some height to the bow of the boat to improve seaworthiness.

For sailing, the mast is made out of two pieces of 2x lumber glued together and then worked into a more cylindrical shape. It’s unstayed, reducing complexity, and although he broke one in extremely high winds, it is more than strong enough for most of his sailing. The ship is gaff-rigged, with a square sail hoisted up the mast by a wooden spar. All of these design choices make it quick and easy to set the sail up when the wind is good or pack it away fast when it’s time to row.

Although there are paid plans available on his website, the methods used in the video show how simple it can be to get into rowing or sailing with a minimal cost. You’ll still want to learn the basics of sailing before taking one of these out into open water. DIY speedboats are also possible and accessible as well, but there’s the added complexity of a motor here to think about, as well as registration requirements that often accompany powered craft.

If you take a video of a spinning wheel, you’ll probably notice that the spokes appear to turn more slowly than the wheel is actually rotating, and sometimes in the wrong direction. This is caused by a near match in the frame rate of the camera and the rate of rotation of the wheel – each time the camera captures a frame, the wheel has rotated a spoke into nearly the same position as in the last frame. If you time the exposures carefully, as [Excessive Overkill] did in his latest video, this effect can seemingly freeze moving objects, such as a fan or saw blade.

Most cameras only allow relatively coarse, fixed adjustments to frame rate, making it difficult to synchronize the shutter to an object’s motion. To get around this, [Excessive Overkill] used an industrial camera (previously used in this aimbot), which has fine frame rate control and external triggering. He connected the external trigger to a laser sensor, which detects a piece of retroreflective tape every time it passes by (for example, on one blade of a fan). When the laser sensor sends a signal, it also triggers a powerful LED flash. The flash is so powerful that dark materials create a hum when exposed to it, as pulses quickly heat the material, but each pulse is also so brief that the flash board doesn’t require any cooling.

Even to the naked eye, these stroboscopic pulses make rotating objects seem to stand still – an effect which made [Excessive Overkill] extra cautious when working around a lathe. When using a suitably long exposure time to avoid rolling-shutter distortion, the effect worked even using a normal camera without frame-rate matching. [Excessive Overkill] took videos of debris flying away from a seemingly motionless bandsaw, milling machine, chop saw, and jigsaw, though it was harder to freeze the rotation of a weed trimmer and a drone.

We’ve seen this effect used to freeze motion a few times before, both for art and for entertainment. If you’d like to recreate it, check out this high-speed LED flash.

Thanks to [Keith Olson] for the tip!