Celebrating Pi Day With A Ghostly Calculator

For the last few years, [Cristiano Monteiro] has marked March 14th by building a device to calculate Pi. This year, he’s combined an RP2040 development board and a beam-splitting prism to create an otherworldly numerical display inspired by the classic Pepper’s Ghost illusion.

The build is straightforward thanks to the Cookie board from Melopero Electronics, which pairs the RP2040 with a 5×5 matrix of addressable RGB LEDs. Since [Cristiano] only needed 4×5 LED “pixels” to display the digits 0 through 9, this left him with an unused vertical column on the right side of the array. Looking to add a visually interesting progress indicator for when the RP2040 is really wracking its silicon brain for the next digit of Pi, he used it to show a red Larson scanner in honor of Battlestar Galactica.

With the MicroPython code written to calculate Pi and display each digit on the array, all it took to complete the illusion was the addition of a glass prism, held directly over the LED array thanks to a 3D-printed mounting plate. When the observer looks through the prism, they’ll see the reflection of the display seemingly floating in mid-air, superimposed over whatever’s behind the glass. It’s a bit like how the Heads Up Display (HUD) works on a fighter jet (or sufficiently fancy car).

Compared to his 2023 entry, which used common seven-segment LED displays to show off its fresh-baked digits of Pi, we think this new build definitely pulls ahead in terms of visual flair. However, if we had to pick just one of [Cristiano]’s devices to grace our desk, it would still have to be his portable GPS time server.

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Moon moving from inside a large glass sphere into screens of two vintage television sets

Blending Pepper’s Ghost, Synths, And Vintage TVs

We were recently tipped off to the work of [Joshua Ellingson], and digging in, we found an extensive collection of art and ongoing experiments, with synthesizers deforming and driving old black-and-white clips played on vintage television sets, objects jumping from screens into the real world and back, and cathode ray tube oscilloscopes drawing graphics in the air (loud sound!) (nitter). It’s recommended that you check out the short showcase videos we embedded below before you continue reading, because transcribing these visuals into words won’t do them justice.

In case you’re not up for a video, however, we shall try transcribing them anyway. Animals, shapes and figures appear in the real world, bound by glass spheres and containers, using the technique known as Pepper’s Ghost. A variety of screens used for creating that illusion – sometimes it’s a tablet, and sometimes it’s an old television set rested upside down on top of a glass aquarium. Vintage television sets are involved quite often in [Ellingson]’s experiments, typically found playing movie scenes and clips from their appropriate eras, or even used as one of the locations that a Pepper’s Ghost-enchanted object could move into — firmly a part of the same imaginary world turned real.

It’s not always that things move from a TV screen into their glass boundary, gaining an extra dimension in the process, but when it happens, the synchronization is impeccable. All of that is backed by — and usually controlled by — Moog synthesizer sounds, knob turns driving video distortions or aspects of an object movement. Not all of his clips have synthesizers, old TVs, or Pepper’s Ghost illusion in them, but every experiment of his contains at least two out of these three, working in unison to create impressions. And as much as the art value is undeniable, [Ellingson] also adds a whole lot of hacker value for us to take away!

[Ellingson] understands what goes into building optical illusions like Pepper’s Ghost — using a variety of different glassware, from Erlenmeyer flasks to teapots, producing a consistent and ongoing stream of new ideas with unique spins on them. His aim is to share and create beyond what his art can achieve, which is why he encourages us to try it out ourselves — with this one minute video of a quick Pepper’s Ghost build, using nothing but a generic tablet, an emptied-out plastic snow globe and a piece of cheap transparency film used for school projectors. If you want to go beyond, he’s made an extensive tutorial on illusions of the kind he does, their simplicities and complexities, and all the different ways you can build one.

We all benefit when an artist finds a technology and starts playing with it, closing the divide between technology and art – and by extension, the divide between technology and nature. Sometimes, it’s flowing light art installations where you are a boulder in route of plankton’s movement, other times, it’s through-hole component-packed printed circuit birds that sing not unlike the non-printed-circuit ones, or manipulation of CRT displays with function generator-driven coils to offset the beam and turn the image into a pattern of lines.

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Oscilloscope And Microscope Augmented With Ghosts

Augmented reality saw a huge boom a few years ago, where an image of the real world has some virtual element layer displayed on top of it. To get this effect to work, however, you don’t need a suite of software and smart devices. [elad] was able to augment a microscope with the output from an oscilloscope, allowing him to see waveforms while working on small printed circuit boards with the microscope.

The build relies on a simplified version of the Pepper’s Ghost illusion. This works by separating two images with a semi-transparent material such as glass, placed at an angle. When looking through the material, the two images appear to blend together. [elad] was able to build a box that attaches to the microscope with a projection of the oscilloscope image augmented on the view of the microscope.

This looks like it would be incredibly useful for PCBs, especially when dealing with small SMD components. The project is split across two entries, the second of which is here. In one demonstration the oscilloscope image is replaced with a visual of a computer monitor, so it could be used for a lot more applications than just the oscilloscope, too. There aren’t a lot of details on the project page though, but with an understanding of Pepper’s Ghost this should be easily repeatable. If you need more examples, there are plenty of other builds that use this technique.

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Productivity, Unfinished Projects, And Letting Go

Most of us have been there, some projects just don’t get finished. Everyone shelves an in-progress build from time to time, and some hackers drop almost every project for fully finishing it. Why does it happen? What can we do about it? Or does it even matter? My own most memorable one is the wine glass rack I was making for my sister’s birthday, still sitting incomplete on a shelf eleven years later.

The answer may lie in what you consider to be a “done” project. Is it a fully completed build with every possible feature implemented and polished? With that rubric you could be counting all of your completed projects on one hand. What are you really getting out of your personal projects? It’s an interesting topic to consider as pivoting your mindset can end up boosting your productivity. So let’s dig in!

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Inexpensive Display Jumps To Life

If you’ve ever been to a local fair or amusement park, chances are you’ve seen an illusion known as Pepper’s Ghost. To perform the illusion, essentially all that’s needed is a thin sheet of plastic or one-way mirror and a light source. Get it right, and you’ll have apparitions popping up in all kinds of interesting places. With just the right software, though, one of those places could be in your own 3D display.

Using just a tablet and a sheet of plastic rolled into a cone, a three-person team was able to create a 3D display using the Pepper’s Ghost illusion. Using special software that the team developed, an image is altered so that when it reflects off of the plastic cone the image appears as a 3D rendering of the original picture. The rendering is perspective-correct and offers a novel way to interact with a 3D model without needing expensive equipment or special glasses.

If you do have some fancy equipment sitting around, like a computer monitor and some plexiglass, similar 3D displays have been made which utilize similar effects. Right now the team that developed this one haven’t made their code open yet, but have promised to release it soon so that others can build their own displays.

Thanks to [bmsleight] for the tip!

Say Hello To This Cortana Hologram

Halo’s Cortana enters the real world with this internet appliance. [Jarem Archer] has built an amazing “holographic” home for Cortana of Halo and Windows fame. The display isn’t really a hologram, it uses the age-old Pepper’s ghost illusion. A monitor reflects onto 3 angled half mirrored panels. This creates a convincing 3D effect. Cortana herself is a 3D model. [Jarem’s] wife provided gave Cortana her moves by walking in front of dual Kinect depth-sensing cameras. This motion capture performance drives the 3D Cortana model on the screen.

The brain behind this hack is the standard Windows 10 Cortana voice assistant. Saying “Hey Cortana” wakes the device up. To make the whole experience more interactive, [Jarem] added a face detection camera to the front of the device. When a face is detected, the Cortana model turns toward the user. Even if several people are watching the device, it would seem as if Cortana was “talking to” one person in the audience.

The cherry on top of this hack is the enclosure. [Jarem] 3D printed a black plastic stage. An Arduino drives RGB LEDs whenever Cortana is activated. The LEDs project a blue glue that works well with the Pepper’s ghost illusion. The result is a project that looks like something Microsoft might have cooked up in one of their research labs.

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3D Display Controlled With The Leap Motion

3d-display-controlled-with-leap-motion

Touch screens are nice — we still can’t live without a keyboard but they suffice when on the go. But it is becoming obvious that the end goal with user interface techniques is to completely remove the need to touch a piece of hardware in order to interact with it. One avenue for this goal is the use of voice commands via software like Siri, but another is the use of 3D processing hardware like Kinect or Leap Motion. This project uses the latter to control the image shown on the 3D display.

[Robbie Tilton] generated a 3D image using Three.js, a JavaScript 3D library. The images are made to appear as if floating in air using a pyramid of acrylic which reflects the light toward the viewer’s eyes without blocking out ambient light in the room. In the past we’ve referred to this as a volumetric display. But [Robbie] points out that this actually uses the illusion called Pepper’s Ghost. It’s not really volumetric because the depth is merely an illusion. Moving your point of view won’t change your perspective unless you go around the corner to the next piece of acrylic. But it’s still a nice effect. See for yourself in the demo after the jump.

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