Big Infinity Mirror Clock Invites You To Gaze Deeply

September 12, 2026 by Donald Papp 10 Comments

[Andy Huot] has a fantastic-looking infinity mirror digital clock that really raises the bar. It uses high quality components, smart use of RGB LED animations, and a clever “stacked diffuser” vertical design to the 7-segment display elements that really enhances the infinity mirror effect. It needs to be seen in action, so check it out.

The end result is expressly portal-like, with the smooth animations of the LEDs really playing into the effect. The size helps, too. It’s 24 inches in diameter, giving it considerable presence.

The stacked diffuser design for each display element really enhances the effect.

A basic infinity mirror design consists of lit elements sandwiched between a reflective back surface and a partially-reflective, partially-transmissive top cover. That same basic principle is used here, but with great care given to ensure nothing so much as a fingerprint spoils the illusion. For example, the top cover is a disk of acrylic with a 90% reflective film affixed to the inside surface. That’s easy enough to DIY with some car tint, but [Andy] found that for the very best results it was worth having high-quality film professionally applied.

We like the use of 3D-printed custom jigs for soldering the segments of RGB LED strips, and holding the pre-measured wires in place with some putty is a great way to keep them in place while working. In case you’re wondering, the mirrored acrylic making up the back wall has holes in it for mounting each segment’s LED strip in a holder, and running the wires to the rear.

The video (embedded below) documents every step of the assembly, and it’s a serious build. While the design files for the 3D-printed parts are not free, there’s certainly enough detail for an enterprising hacker to replicate the design in their own way.

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The Heavy Disco-Ball Satellite Designed To Do… Nothing

September 12, 2026 by Donald Papp 19 Comments

Launched in 1976, LAGEOS-1 (LAser GEOdynamic Satellite) is unusual in that it contains no instrumentation, no electronics, no power supply, and no means of propulsion. It’s spherical, weighs just under 407 kg, and looks a bit like a disco ball. It may not be accurate to say it does nothing, but unlike most satellites its role is entirely passive. It’s also one of the oldest scientific satellites still in service.

The lens-like objects covering the surface of LAGEOS-1 are corner cube retroreflectors, which have the nifty effect of always reflecting incident light right back towards its source.

Ground stations fire short laser pulses at it and measure the time it takes for the light to return, a form of time-of-flight ranging. Since LAGEOS-1’s orbit is highly stable, it provides a reliable reference point for measuring even tiny changes in the Earth itself. The size, shape, rotation, and more of our planet can be measured as a result. LAGEOS data (LAGEOS-2 was launched in 1992) has also been used in tests of general relativity.

Its orbit and construction were deliberately chosen so that atmospheric drag and other disturbances would be minimal. The simple, maintenance-free design combined with an extraordinarily stable orbit means LAGEOS is expected to circle our world for millions of years to come.

LAGEOS-1 also contains a message to the future in the form of two identical plaques prepared by Dr. Carl Sagan just in case there’s anyone around to find it some day. Check out the short 1975 video from NASA, embedded just below.

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How To Fold Curved Lines In Metal Without Fancy Tools

September 11, 2026 by Donald Papp 16 Comments

Folding a sheet of metal in a straight line is one thing, but how does one fold multiple curved lines into a sheet of aluminum without fancy machines? [John] demonstrates how to do exactly that with little more than hand tools and a fair bit of patience. The secret is drilling a lot of small holes along each fold line.

First, a bit of background. [John] wanted to fabricate a curved piece of aluminum as cover that would match the sleek aerodynamic lines of a Belly Tank Lakester. The trick is that there isn’t a single straight line to be found, and the fold lines are all curves. How can one do such folding with only hand tools?

[John] found that fabrication was possible by drilling small holes all along each fold line, then carefully bending as needed. The line of holes weakens the metal, acting like a score line, and allow the required curves to be made cleanly. There’s some finishing work and straightening involved, but the hard part of making the actual folds is taken care of.

One method that didn’t work was cutting a shallow groove in the metal to create something like a pre-scored fold line. [John] tried this and found that while the metal does indeed fold along the weakened line, the aluminum tends to crack in the process. When making a line of holes instead, the metal between each hole bends nicely.

This technique does mean the finished part ends up with small perforations along each fold, but the part is mounted on the bottom of the car and [John] says that he’d have to look quite closely to notice. A little polishing goes a long way, too.

We have covered many ways to bend sheet metal and while machinery exists to do it exceedingly well, great results can be had with little more than simple tools and some patience.

Watch [John] go through the process in the video embedded below, or skip to 7:55 if you just want to see the end result.

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Custom AMOLED Wearable Makes Great Icebreaker

September 10, 2026 by Donald Papp 12 Comments

Nifty little AMOLED screens are easy to get nowadays, and [Sophie D] demonstrates they are both thin and light enough to be worn with OpenChoker, a design for a choker necklace that was a hit at DEF CON.

The choker consists of an AMOLED touchscreen flanked by short RGB LED strips. Behind the display is the PCB which contains an RP2350 and micro SD card slot for external storage, and at the rear of the choker is an 18650 cell to power it all. The display plays an eye-catching animation that gets generated on the fly while the LEDs sparkle away.

[Sophie] shares a number of interesting takeaways from designing and building this device. One is that the bulk of the PCB design work was interfacing to the display, since no existing footprint or reference design could be found. So if you find yourself with a Hello Lighting HL020E21-02 2.14″ touchscreen display you’re hankering to use in your own project, do yourself a favor and check out [Sophie]’s board design instead of starting from scratch.

Battery life was more than enough for a device like this. A single 18650 cell powered the choker effortlessly for a 16-hour stretch and still the cell measured a robust 3.7 V. While a light-up choker used indoors isn’t a great candidate for wearable solar power, it’s encouraging that there’s no need for a tethered battery pack.

Another tip to consider relates to the screen’s touch sensitivity. In short, the capacitive touch screen responded perfectly when plugged into a development computer, but when mounted and isolated on the choker it responded so poorly as to be useless. It didn’t keep the rest of the choker from doing its job, but it might be worth keeping in mind as something to watch out for with a device like this.

There’s one final mystery [Sophie] ran into: with only one day to spare, glue used to affix some wires ended up melting away the wire insulation, revealing bare copper. We’re not sure what happened there, but if nothing else it’s a reminder that Murphy’s Law is always ready to strike when one is on a deadline.

The Different Ways To Look At Negative Resistance

September 8, 2026 by Donald Papp 21 Comments

[lcamtuf] has an in-depth look at the concept of negative resistance that goes somewhat further than one might expect. Normally, as voltage across a resistance increases so too does the current. Negative resistance is the concept of current decreasing as voltage increases. But beyond the raw concept, there are a few other ways to look at this idea.

The usual way to think about it is negative differential resistance (NDR). Not everything has a linear relationship between voltage and current, and for a device to exhibit NDR means that in certain ranges the I–V curve actually slopes downward; increasing one of voltage or current decreases the other. This kind of thing occurs in neon lamps. Once they are glowing, increasing current can result in decreasing voltage.

True negative resistance, that of a literal -100 Ω resistor, does not exist. Not in the sense of a passive component, anyway. Such a device would supply power into a circuit rather than dissipating it, and would therefore require an external power source to do so. If that’s not a deal breaker, then it’s actually fairly simple to build one. [lcamtuf] provides a design for a device that uses an op-amp to exhibit ideal constant negative resistance. Naturally it only does so within its operating range; going beyond risks letting out the magic smoke.

Is making a literal negative resistor of practical use? Perhaps only in very specialized situations. But it is worth having a basic understanding if for no other reason than it rears its head in unusual places: the strange tunnel diode comes to mind.

Are Desktop PC-ABS Prints Outperformed By Industrial FDM? Not Really

September 8, 2026 by Donald Papp 18 Comments

[Igor] of [My Tech Fun] set out to discover what differences, if any, can be found between parts printed in PC-ABS filament on an industrial 3D printer, and those from prosumer-grade machines and filament. His video is full of his usual attention to detail as he compares a test suite of parts printed at home in Polymaker PC-ABS with those from a Stratasys Fortus 450mc using proprietary PC-ABS filament.

PC-ABS is a filament that strives to deliver the benefits of both polycarbonate and ABS. It’s durable and has fantastic impact resistance, but it costs a bit more than either PC or ABS and requires a heated chamber.

[Igor] has previously compared industrial ABS with comsumer ABS, but what made him curious about PC-ABS in particular was the large difference in print temperatures between Polymaker PC-ABS, and Stratasys’s own proprietary PC-ABS.

[Igor] prints Polymaker filament at 280º C in a 60-65º C chamber, whereas the Stratasys filament prints at 325º C with a chamber temperature of 95º C. That’s quite a difference. The industrial printer has over double the print time, to boot. Would test objects printed from the industrial filament, on an industrial machine, be noticeably different from those printed at home?

To find out, [Igor] orders a test suite of parts from a company with a Stratasys Fortus 450mc (who was also kind enough to take a short video of the machine in action) and prints his own on both a Prusa Core One L, and a Bambu Labs H2D. He then proceeds to compare them in a variety of ways while testing them to destruction.

What’s the bottom line? The industrial prints have better dimensional accuracy, but the home prints have the edge in appearance. When it comes to performance the differences are mostly minor, and not always in the industrial system’s favor. Broadly speaking, PC-ABS from the home workshop compares very favorably from an expensive industrial system and proprietary filament, at a fraction of the price. See it for yourself in the video, embedded just below.

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Voicebox FX Is A Blueprint For CircuitPython I2S Audio

September 5, 2026 by Donald Papp 1 Comment

[Adafruit]’s Voicebox FX gadget is a fun, well-documented project that serves another useful purpose: being a fantastic reference design for audio on CircuitPython, with I²S audio components. Be sure to check it out if you have a project that involves any of that and could use a few pointers, or if you just want to jog a few ideas loose.

I²S (Inter-IC Sound) is a protocol aimed squarely at moving audio data between components as digital signals. Our own [Jenny List] can tell you everything you need to know about I²S. It’s a relatively simple interface that is not at all fussy about actually being used for audio, and that has led to it being put to some unusual uses.

The Voicebox FX uses an I²S microphone, an I²S amplifier, and an RP2350 microcontroller to record and play sound as well as offer a variety of effects controlled by physical inputs. It’s all wrapped up in a slick 3D printed case, and while it’s a fantastic reference design, it looks like a fun toy in its own right.

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