The best part is that the status can been seen on both sides of the door so you don’t forget to keep it updated. Or maybe it’s the super-low part count. There’s no BLE, LoRa, or Wi-Fi, just two sets of red and green LEDs, a three-way switch, and a power source. Well, and current-limiting resistors of course.
[Bob] already had all the components on hand, including the nifty enclosure, which is another great thing about this build. Like [Bob] says, you could house the control side of this circuit in just about anything you’ve got lying around.
For as many of them as we’ve seen, we still love a good persistence of vision display project. There’s something fascinating about the combination of movement and light creating the illusion of solid surfaces, and there’s always fun to be had in electromechanical aspects of a POV build. This high-resolution spherical POV display pushes all those buttons, and more.
Called “Flicker” for obvious reasons by its creator [Dan Foisy], this POV display started with a pretty clear set of goals in terms of resolution and image quality, plus the need to support animated images, all in a spherical form factor. These goals dictated the final form of the display — a PCB disc spinning vertically. The shaft has the usual slip rings for power distribution and encoders for position feedback. The PCB, though, is where the interesting stuff is.
[Dan] chose to use an FPGA to slice and dice the images, which are fed from a Raspberry Pi’s HDMI port, to the LED drivers. And the LEDs themselves are pretty slick — he found parts with 1.6 mm lead spacing, making them a perfect fit for mounting on the rim of the PCB rather than on either side. A KiCAD script automated the process of laying out the 256 LEDs and their supporting components as evenly as possible, to avoid imbalance issues.
The video below shows Flicker in action — there are a few problem pixels, but on the whole, the display is pretty stunning. We’ve seen a few other spherical POV displays before, but none that look as good as this one does.
Don’t you hate getting up in the middle of the night to use the bathroom? The worst part is not being able to see what you’re doing, but if you turn on a light, you’ll lose your night vision. Nightlights are supposed to be the best solution, but are usually too bright for 3 AM excursions and can end up leaking light into the bedroom. What the bathroom needs is a purpose-built nightlight that uses red light so you don’t lose your night vision.
This simple, wall-mounted night light is just the thing. All it takes is two AA batteries, a resistor, a red LED, and an SPST push button. [Vchaney] even made their own battery contacts. The genius part of this build is in the adjustable LED, which is fitted into a ball that moves around in a socket so you can aim it wherever you need to see. All the files are available if you want to print one for yourself.
[Jan Mrázek] is no stranger at all to home-grown improvements with his Elegoo Mars SLA 3D printer, and there is a lot going on in his experimental multi-LED upgrade which even involved casting his own lens array. In the end it did speed up his prints by a factor of three to four, though he cooked an LCD to failure in the process. Still, it was a fun project done during a COVID-19 lockdown; as usual there is a lot to learn from [Jan]’s experiences but the mod is not something he necessarily recommends people do for themselves.
[Jan] started by wondering whether better print quality and performance could be obtained by improving the printer’s UV light source. The stock printer uses a single large UV LED nestled into a reflector, but [Jan] decided to try making a more precise source of UV, aiming to make the UV rays as parallel as possible.
Custom LED array molded in clear epoxy.
To do this, he took a two-pronged approach. One was to replace the single large UV LED with a 4×7 array of emitters plus heat sink and fans. The other was to make a matching array of custom lenses to get the UV rays as parallel as possible.
Casting one’s own lens array out of clear epoxy was a lot of work and had mixed results, but again, it was a lockdown project and the usual “is-this-really-worth-it” rules were relaxed. In short, casting a single custom lens out of clear epoxy worked shockingly well, but when [Jan] scaled it up to casting a whole 4×7 array of them, results were mixed. Mold deformation and artifacts caused by the areas between individual lenses robbed the end result of much of its promise.
More success was had with the array of UV emitters, which enabled faster curing thanks to higher power, but the heat needs to be managed. The stock emitter of the printer is about 30 W, and [Jan] was running his new array at 240 W. This meant a blazing fast one second exposure time per layer, but the heat generated by the new lighting was higher than anticipated. After only ten hours the LCD failed, probably at least in part due to the heat. [Jan] halved the power of the array down to 120 W and added an extra fan, which appears to have done the trick. Exposure time is two to three seconds per layer, and it’s up to 150 hours of printing without problems.
Again, it’s not a process [Jan] necessarily recommends to others (and he definitely recommends buying lenses if at all possible instead of casting them) but as usual there is a lot to learn from his frank sharing of results, both good and bad. We’ve seen 3D-printed lenses as well as adding WiFi connectivity to one of these hobbyist printers, and it’s great to see the spirit of hacking alive and well when it comes to these devices.
Rayleigh scattering is emulated by passing the light through a glass chamber filled with soapy water – taking advantage of the Tyndall effect.
The great distance between the Sun and the Earth means that the sun’s rays are essentially parallel from our local vantage point. Replicating this, and the soothing nature of a blue sky, were [Matt]’s primary goals with the project. To achieve this, an old satellite dish was pressed into service as a parabolic reflector, coated with mirror-finish vinyl strips. A 500W white LED with a good color rendering index was fitted at the focal point, outfitted with a water cooling system to shed heat. With a point source at its focal point, the parabolic reflector bounces the light such that it the rays are parallel, giving the sense that the light source is coming from an effectivelyl infinite distance away. To then achieve the blue sky effect, the light was then passed through a glass chamber filled with soapy water, which scatters the light using the Tyndall effect. This mimics the Rayleigh scattering in Earth’s atmosphere.
The final result is amazing, with [Matt] shooting footage that appears to be filmed in genuine daylight – despite being shot at night or on rainy days. He also features a cutdown build that can be achieved in a far cheaper and compact form, using Fresnel lenses and blue film. We’ve featured [Matt]’s daylight experiments before, though we’re amazed at the new level reached. Video after the break.
For the vast majority of us, computer memory is a somewhat abstract idea. Whether you’re declaring a variable in Python or setting a register in Verilog, the data goes — somewhere — and the rest really isn’t your problem. You may have deliberately chosen the exact address to write to, but its not like you can glance at a stick of RAM and see the data. And you almost certainly can’t rewrite it by hand. (If you can do either of those things, let us know.)
These limitations must have bothered [Andy Geppert], because he set out to bring computer memory into the tangible (or at least, visible) world with his interactive memory badge Core 64. [Andy] has gone through a few different iterations, but essentially Core 64 is an 8×8 grid of woven core memory, which stores each bit via magnetic polarization, with a field of LEDs behind it that allow you to visualize what’s stored. The real beauty of this setup is that it it can be used to display 64 pixel graphics. Better yet — a bit can be rewritten by introducing a magnetic field at the wire junction. In other words, throw a magnet on a stick into the mix and you have yourself a tiny drawing tablet!
The incandescent light bulb was one of the first early applications of electricity, and it’s hard to underestimate its importance. But before the electric light, people didn’t live in darkness — they thought of ways to redirect sunlight to brighten up interior spaces. This was made possible through the understanding of the basic principles of optics and the work of skilled glassmakers who constructed prism tiles, deck prisms, and vault lights. These century-old techniques are still being applied today for the diffusion of LEDs or for increasing the brightness of LCD displays.
Semantics First!
People in optics are a bit sloppy when it comes to the definition of a prism. While many of them are certainly not geometric prisms, Wikipedia defines it as a transparent optical element with flat, polished surfaces of which at least one is angled. As can be seen in the pictures below some of the prisms here do not even stick to this definition. Browsing the catalog of your favorite optics supplier you will find a large variety of prisms used to reflect, invert, rotate, disperse, steer, and collimate light. It is important to point out that we are not so much interested in dispersive prisms that split a beam of white light into its spectrum of colors, although they make great album covers. The important property of prisms in this article is their ability to redirect light through refraction and reflection.
A Safe Way to Bring Light Under Deck
A collection of deck lights used to direct sunlight below deck in ships. Credit: glassian.org
One of the most important uses of prism lighting was on board ships. Open flames could have disastrous consequences aboard a wooden ship, so deck prisms were installed as a means to direct sunlight into the areas below decks. One of the first patents for deck lights “THE GREAT AND DURABLE INCREASE OF LIGHT BY EXTRAORDINARY GLASSES AND LAMPS” was filed by Edward Wyndus as early as 1684. Deck prisms had typical sizes of 10 to 15 centimeters. The flat top was installed flush with the deck and the sunlight was refracted and directed downward from the prism point. Because of the reversibility of light paths (“If I can see you, you can see me”) deck prisms also helped to spot fires under deck. Continue reading “Prism Lighting – The Art Of Steering Daylight”→
All this ongoing forced togetherness is great, but sometimes you just need to be able to pretend you’re alone so you can get some work done. So, how do you keep family members out of your home office? Our own [Bob Baddeley]’s free/busy indicator is about as simple as it gets.
tangible (or at least, visible) world with his 
