Building A Glowing Demon Core Lamp

The so-called Demon Core was a cursed object, a 6.2 kilogram mass of plutonium intended to be installed in a nuclear weapon. Instead, slapdash experimental techniques saw it feature in several tragic nuclear accidents and cause multiple fatalities. Now, you can build yourself a lamp themed after this evil dense sphere.

A later recreation of the infamous “Slotin Accident” that occurred with the Demon Core. Credit: Public Domain, Los Alamos National Laboratory

Creator [skelly] has designed the lamp to replicate the Slotin incident, where the spherical Demon Core was placed inside two half-spheres of beryllium which acted as neutron reflectors to allow it to approach criticality. Thus, the core is printed as a small sphere which is thin enough to let light escape, mimicking the release of radiation that doomed Louis Slotin. The outer spheres are then printed in silvery PLA to replicate the beryllium half-spheres. It’s all assembled atop a stand mimicking those used in the Los Alamos National Laboratory in the 1940s.

To mimic the Core’s deadly blue glow, the build uses cheap LED modules sourced from Dollar Tree lights. With the addition of a current limiting resistor, they can easily be run off USB power in a safe manner.

The Demon Core has become a meme in recent times, perhaps as a new generation believes themselves smart enough not to tinker with 6.2 kilograms of plutonium and a screwdriver. That’s not to say there aren’t still dangerous nuclear experiments going on, even the DIY kind. Be careful out there!

Share Screen To RGB Panel With Pi Pico W

RGB LEDs are great for adding a bit of color to your life, and it’s even more satisfying to use a matrix of them as a graphic display. [bitluni] built an RGB LED display with Pi Pico to which you can share a pixelated version of your PC’s screen.

[bitluni] wanted to gain some experience with MicroPython on the Raspbery Pi Pico W, and had previously used WebSockets to transmit display data over WiFi. Unfortunately, the available MicroPython WebSockets implementation didn’t leave enough RAM for the rest of the code. Instead, he set up a simple HTTP server on the Pico that receives the pixel data as a POST request. This makes for a slow refresh rate but still looks great, especially with the 3D printed rear-projection frame.

To send display data from the computer, [bitluni] uses a simple locally hosted HTML page that takes the Pico’s IP address, and prompts you to select the display or window you want to share. It uses JavaScript to grab the display data, generate the required low-res pixel values, and send the POST request.

This looks like a fun weekend project to add to your lab or home and only costs about $20 in parts. It’s basically a scaled-down version of his giant ping pong ball wall display.

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A clock displaying a micro QR code

LED Clock Uses Micro QR Codes To Show The Time

As you probably know, we love our clocks here at Hackaday. Odd display technologies are always interesting to see, as are unusual encoding techniques such as binary, ternary or higher-radix number systems. Still, clocks are typically meant to be human-readable, even if their encoding might be a little eccentric.

[Kitchi] however built an LED-based clock that is not human-readable, at least not without quite a bit of training. This is because it displays the time by generating a QR code, which only becomes readable to most humans through the use of a smartphone app. Of course, this negates the need for a clock since your smartphone will already have one anyway — but whoever said a clock needs to be useful?

To be fair, the display could conceivably be read by a determined human, since the QR format used is the tiny Micro QR M2 version that measures only 13×13 pixels. It’s capable of storing ten decimal digits, just enough to hold the date and time in mmddhhmmss format. The fixed part of the QR code is made of paper, while the variable part is formed through a grid of 90 white LEDs. The LEDs are mounted on a piece of prototype board along with a PIC 16F1504 microcontroller, two TM1637 LED drivers and a DS1307 real-time clock with battery backup.

If decoding QR codes is not your thing, or you simply haven’t got your smartphone on you, then the QR clock can also be set to a more human-readable format by adding a jumper. The time will then scroll across the LED screen in ordinary decimal format.

The video in the link is in Japanese, with no automatic translation available, but the build process is clearly shown and should be understandable even if you can’t follow the cheerful robotic narrator. We’ve seen a couple of QR-code based clocks before, some with an LCD screen and some with retro styling, but all of those use the larger standard QR code which definitely no human can decode visually. Or can you? Let us know in the comments!

Thanks for the tip, [J. Peterson]!

Circuit-less PCB Featured As Faceplate For A Digital Clock

If there’s no circuitry on a printed circuit board, does it cease being a “PCB” and perhaps instead become just a “PB”?

Call them what you will, the fact that PCBs have become so cheap and easy to design and fabricate lends them to more creative uses than just acting as the wiring for a project. In this case, [Jeremy Cook] put one to work as the faceplate for his “742 Clock,” a name that plays on the fact that his seven-segment display is 42 mm tall, plus it’s “24/7” backward.

In addition to the actual circuit board that holds the Wemos ESP32 module and the LEDs, a circuit-less board was designed with gaps in the solder mask to act as light pipes. Sandwiched between the boards is a 3D printed mask, to control the light and direct it only through the light pipes. [Jeremy] went through a couple of iterations of diffuser and mask designs, finally coming up with a combination that works well and looks good. He mentions a possible redesign of the faceplate board to include a copper backplane for better opacity, which we think is a good idea. We’d also like to see how different substrates work; would boards of different thickness or using FR-4 with different glass transition temperatures work better? Check out the video below and see what you think.

We’re seeing more and more PCBs turn up as structural elements, from enclosures to control panels and even tools, and we approve of this trend. But what we really approve of is what [Jeremy] did here by making this clock just a dumb display that gets network time over NTP. Would that all three digital clocks in our kitchen did the same thing — maybe then they wouldn’t each be an infuriating minute out of sync with the others.

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DIY LED Bulb Lacks Correct Lugs, So M3 Bolts To The Rescue

[Damo] has an interesting LED bulb project with a neat twist: he converted some outdoor lighting to 12 V LED lighting with some self-designed bulb replacements and decided to reuse the existing GU10 sockets and wiring. That meant putting GU10 lugs onto his custom PCBs, but he ran into a snag.

These GU10 bulb lugs are tough to buy in small quantities. Luckily, M3 socket head bolts are a near-perfect match.

Those distinctive lugs that twist into GU10 sockets? [Damo] simply couldn’t find anywhere offering to sell them in small quantities. So he did what any enterprising hacker would do and found a substitute that was both accessible and economical: M3 bolts. Apparently, socket-headed M3 bolts are pretty much identical in size to GU10 lugs. Who’d have thought?

[Damo]’s retrofit worked great, and thanks to M3 bolts he was able to re-use the existing weatherproof wiring and sockets in his yard. His design files are here on GitHub.

We do love using things for other than their intended purpose, but as [Damo] points out, GU10 sockets are normally connected to mains power. So if you decide to use his design (or use GU10 sockets for your own purposes), be aware that you’ll have hardware that looks interchangeable with other (mains-connected) sockets, but isn’t. Be mindful of that, and take appropriate precautions. Avoiding electrical oopsies is always worth putting effort into, after all.

You Can Build A Giant 7-Segment Display Of Your Very Own

Sometimes you need to display a number nice and large, making it easily readable at a good distance. [Lewis] has just the thing for that: a big expandable 7-segment display.

The build is modular, allowing it to be extended from 2 to 10 digits and beyond. The digits themselves are made of 3D-printed parts assembled onto acrylic. These can then be ganged up in a wooden frame for displaying larger numbers with more digits. Individual elements are lit by addressable LEDs, and the project can be built using an Arduino Nano or an ESP8266 for control. The latter opens up possibilities for controlling the screen over WiFi, which could prove useful.

[Lewis] has built his own version for a local swim club, where it will be used as a laptimer. Other applications could be as a scoreboard in various sports, or to confuse your neighbours by displaying random numbers in your front yard.

We’ve seen a similar build from [Ivan Miranda] that served well as a workshop clock, too. Video after the break.

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Washington, DC Finally Gets Its Own PCB Metro Map

There was a time, not so long ago, when folks who wanted to make their own custom PCBs would have found themselves in the market for a bucket of acid and a second-hand laser printer. These days, all you have to do is click a few buttons in your EDA program of choice and send the files off for fabrication. It’s easy, cheap, and nobody ends up with chemical burns.

This has obviously had a transformative effect on the electronics hobby — when you can place traces on a PCB like an artist using a brush, it’s only a matter of time before you get projects like [Logan Arkema]’s DCTransistor. This open source board uses carefully arranged RGB LEDs to recreate the Washington Metropolitan Area Transit Authority (WMATA) metro map, and thanks to an ESP8266 connected to their API, can display the positions of trains in real-time.

If you’re getting a sense of déjà vu here, it’s not just in your head. We’ve seen similar maps created for other major metropolitan areas, and [Logan] certainly isn’t trying to take credit for the idea. In fact, he was a bit surprised to find that nobody had ever made one for the DC area — so he decided to take on the challenge himself. He reasoned it would be a good way to hone his PCB design skills and become more comfortable with embedded development. We’d say the end result proves his theory correct, and makes one more city that can boast about its IoT cartography.

Looking to hang a DCTransistor on your own wall? [Logan] says he’ll be dropping the board design files and schematics into the project’s GitHub repository soon, and he also plans on selling pre-made boards in the near future.

We covered this London “tube” map back in 2020, and were impressed by the attention to detail that went into similar displays for Tokyo, Singapore, and the San Francisco Bay Area a year later. Perhaps it’s time to map out your own hometown in LEDs?