Building A 7-Segment Shadow Clock

August 10, 2025 by Lewin Day 6 Comments

There are plenty of conventional timepieces out there in the world; we’ve also featured a great many that are aesthetically beautiful while being unreadably esoteric. This neat “shadow clock” from [Smart Solutions for Home] is not conventional, but it’s still a clock you could use every day.

The display is made of four seven-segment digits, which have a subtle appearance. Each segment uses a solenoid to extend it forward out of the display, or to retract it flush with the faceplate. This creates a numerical display in all one color, with the physical protrusion doing the job of making the numbers visible. This is perhaps where the “shadow clock” name comes from, though you notice the protruding segments moreso than the shadows they cast on the faceplate.

Running the show is an ESP32, paired with H-bridges to drive the solenoids that make up the 7-segment displays. The H-bridges are driven via shift registers to reduce the number of GPIO pins needed. Unlike many other ESP32 clock builds, this one uses a DS3231 real-time clock module to keep accurate time, rather than solely relying on Internet-based NTP time servers. Configuring the clock can be done via a web interface. Design files are available online.

If you think you’ve seen this recently, maybe you’re thinkig of this prototype for a very similar display by [indoorgeek]. And that’s not the only way to make shadow clocks either. After all, the term is not enforced or defined by any global horological organization. Maybe that’s a good thing! Video after the break.

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2025 One Hertz Challenge: Estimating Pi With An Arduino Nano R4

August 9, 2025 by Lewin Day 10 Comments

Humanity pretty much has Pi figured out at this point. We’ve calculated it many times over and are confident about what it is down to many, many decimal places. However, if you fancy estimating it with some electronic assistance, you might find this project from [Roni Bandini] interesting.

[Roni] programmed an Arduino Nano R4 to estimate Pi using the Monte Carlo method. For this specific case, it involves drawing a circle inscribed inside a square. Points are then randomly scattered inside the square, and checked to see if they lie inside or outside the circle based on their position and distance of the circle’s outline from the center point of the square. By taking the ratio of the points inside the circle to the total number of points, you get an approximation of the ratio of the square and circle’s areas, which is equal to Pi/4. Thus, multiply the ratio by 4, and you’ve got your approximation of Pi.

[Roni] coded a program to run the Monte Carlo simulation on the Arduino Nano R4, taking advantage of the mathematical benefits of its onboard Floating Point Unit. It generates 100 new samples for the Monte Carlo approximation every second, improving the estimation of pi as it goes. It then displays the result on a 7-segment display, and beeps as it goes. [Roni] readily admits the project is a little too close in appearance to a classic Hollywood bomb.

We’ve seen some other neat Pi-calculating projects before, too.

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3D Printing A Giant Beyblade Arena

August 9, 2025 by Lewin Day 4 Comments

Beyblade spinning tops are pretty easy to find at toy shops, department stores, and even some supermarkets. However, the arenas in which the tops do battle? They’re much harder to come by, and the ones on sale in any given market often leave a lot to be desired. [LeftBurst] got around this problem by printing a grandiose Beyblade arena.

[LeftBurst]’s desire was to score a Beyblade stadium more similar to those featured in the anime, which are much larger than those sold as part of the official toy line. [Buddha] was enlisted to model the massive arena, but it then needed to be printed. Given its size, printing it in one piece wasn’t very practical. Instead, [LeftBurst] decided to print it in segments which would then have to be assembled. Super glue was used to put all the parts together, but there was more left to do. The surface finish and joins between the parts would cause issues for tops trying to move across the surface. Thus ensued a great deal of post-processing with primer, putty, and a power sander.

The final result is a massive stadium that plays well, and is ideal for larger multi-Beyblade battles that are more akin to what you’d see in the anime. If you’re playing at this scale, you might appreciate some upgraded launcher technology, too.

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One File, Six Formats: Just Change The Extension

August 8, 2025 by Lewin Day 39 Comments

Normally, if you change a file’s extension in Windows, it doesn’t do anything positive. It just makes the file open in the wrong programs that can’t decode what’s inside. However, [PortalRunner] has crafted a file that can behave as six different filetypes, simply by swapping out the extension at the end of the filename.

The basic concept is simple enough. [PortalRunner] simply found a bunch of different file formats that could feasibly be crammed in together into a single file without corrupting each other or confusing software that loads these files.

It all comes down to how file formats work. File extensions are mostly meaningless to the content of a file—they’re just a shorthand guide so an operating system can figure out which program should load them. In fact, most files have headers inside that indicate to software what they are and how their content is formatted. For this reason, you can often rename a .PNG file to .JPEG and it will still load—because the operating system will still fire up an image viewer app, and that app will use headers to understand that it’s actually a PNG and not a JPEG at heart, and process it in the proper way.

[PortalRunner] found a way to merge the headers of various formats, creating a file that could be many different types. The single file contains data for a PNG image, an MP4 video, a PDF document, a ZIP archive, a Powerpoint presentation, and an HTML webpage. The data chunks for each format are lumped into one big file, with the combined headers at the very top. The hijinx required to pull this off put some limitations on what the file can contain, and the files won’t work with all software… but it’s still one file that has six formats inside.

This doesn’t work for every format. You can’t really combine GIF or PNG for example, as each format requires a different initial set of characters that have to be at the very beginning of the file. Other formats aren’t so persnickety, though, and you can combine their headers in a way that mostly works if you do it just right.

If you love diving into the binary specifics of how file formats work, this is a great project to dive into. We’ve seen similarly mind-bending antics from [PortalRunner] before, like when they turned Portal 2 into a webserver. Video after the break.

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Tearing Down A Mysteriously Cheap $5 Fiber Optic To Cable TV Adapter

August 8, 2025 by Lewin Day 26 Comments

In his regular browsing on AliExpress, [Ben Jeffrey] came across something he didn’t understand—a $5 fiber optic to RF cable TV adapter. It was excessively cheap, and even more mysteriously, this thing didn’t even need power. He had to know how it worked, so he bought one and got down to tinkering with it.

[Ben] needed some hardware to test the device with, so he spent $77 on a RF-to-fiber converter and a cheap composite-to-RF modulator so he could test the $5 fiber-to-RF part. A grand expenditure to explore a $5 device, but a necessary sacrifice for the investigation. Once [Ben] hooked up a fiber optic signal to the converter, he was amazed to see it doing its job properly. It was converting the incoming video stream to RF, and it could readily be tuned in on a TV, where the video appeared clean and true.

It was disassembly that showed how simple these devices really are. Because they’re one-way converters, they simply need to convert a changing light signal into an RF signal. Inside the adapter is a photodiode which picks up the incoming light, and with the aid of a few passives, the current it generates from that light becomes the RF signal fed into the TV. There’s no need for a separate power source—the photodiode effectively works like a solar panel, getting the power from the incoming light itself. The part is ultimately cheap for one reason—there just isn’t that much to it!

It’s a neat look at something you might suspect is complex, but is actually very simple. We’ve explored other weird TV tech before, too, like the way Rediffusion used telephone lines to deliver video content. Video after the break.

2025 One Hertz Challenge: The Real-Time Clock The VIC-20 Never Had

August 8, 2025 by Lewin Day 6 Comments

Like many early microcomputers, the Commodore VIC-20 did not come with an interna real-time clock built into the system. [David Hunter] has seen fit to rectify that with an add-on module as his entry to the 2025 One Hertz Challenge.

[David]’s project was inspired by a product that Hayes produced in the 1980s, which provided a serial-port based real-time clock solution for computers that lacked one on board. The heart of the project is an Arduino Uno, which itself uses a Dallas DS3231 RTC module to keep accurate time. [David] then drew from an IEC driver developed by [Lars Pontoppidan] for the MM2IEC project. This enables the Arduino to report the time to the VIC-20 via its IEC port.

The project is a neat way to provide a real-time clock source to programs written in Commodore BASIC. It’s also perfectly compatible with the IEC bus, so it can be daisy chained along with printers and disk drives without issue. [David] hasn’t tested it with a Commodore 64, but he suspects it should work just as well on that platform, too.

If you’ve ever wanted to build something clock-based for the VIC-20 but didn’t know how, this is a great piece of hardware to solve that problem. Meanwhile, you might find joy in reading about real-time clock hacks for other systems like the Raspberry Pi. Meanwhile, if you’re working on your own nifty timekeeping projects, don’t hesitate to let us know!

Talking Robot Uses Typewriter Tech For Mouth

August 8, 2025 by Lewin Day 15 Comments

Many decades ago, IBM engineers developed the typeball. This semi-spherical hunk of metal would become the heart of the Selectric typewriter line. [James Brown] has now leveraged that very concept to create a pivoting mouth mechanism for a robot that appears to talk.

What you’re looking at is a plastic ball with lots of different mouth shapes on it. By pivoting the ball to different angles inside the head of a robot, it’s possible to display different mouth shapes on the face. By swapping mouth shapes rapidly in concert with recorded speech, it’s possible to make the robot appear to be speaking. We don’t get a great look at the mechanism that operates the ball, but Selectric typeball operation is well documented elsewhere if you seek to recreate the idea yourself.

The real benefit of this mechanism is speed. It might not look as fluid as some robots with manually-articulated flexible mouths, but the rapid mouth transitions really help sell the effect because they match the pace of speech. [James] demonstrated the finished product on Mastodon, and it looks great in action.

This isn’t the first time we’ve featured [James Brown]’s work. You may recall he got DOOM running on a tiny LEGO brick a few years back.

Thanks to [J. Peterson] for the tip!