As futuristic as holographic technology may sound, in a sense it’s actually already in widespread commercial use. Concerts and similar events already use volumetric projection, with a fine mesh (hologram mesh or gauze) acting as the medium on which the image is projected to give the illusion of a 3D image. The widespread availability of this technology has now enabled Germany’s Roncalli circus to reintroduce (virtual) animals to its shows after ceasing the use of live lions and elephants in 1991 and other animals in 2018.
For the sticklers among us, these are of course not true holograms, as they do not use a recorded wavefront, nor do they seek to recreate a wavefront. Rather they employ as mentioned volumetric projection to essentially project in ‘thin air’, giving the illusion of a tangible object being present. By simultaneously projecting multiple views, to an observer standing outside the projection mesh, it would thus appear that there is a physical, three-dimensional object which can be observed. In the case of the Roncalli circus there are 11 projectors lining the circumference of the mesh.
To a circus the benefits of this approach are of course manifold, as not only do they no longer have to carry lots of animals around every time the circus moves to a new location – along with the on-site demands – but they get to experiment with new shows and new visuals that were never before possible. Ironically, this could mean that after 3D fizzled out at movie theaters, circuses and similar venues may be in a position to make it commonplace again for the masses.
You’ve seen it a million times in science fiction movies and TV shows: a moving holographic display. From Princess Leia asking for help to virtual tennis on Total Recall, it is a common enough idea. [Dan Smalley]’s team at BYU has made progress in projecting moving 3D images in thin air. While they might not be movie quality, they are a start, and, after all, you have to start somewhere.
The display traps a small particle in the air with a laser beam and then moves that particle around, leaving behind an illuminated path in the air. You can see the effect in the video below. The full paper explains how a type of ray tracing allows the relatively small optical trap display to appear larger and more fluid. While it does make images seem to appear behind the display’s actual volume, it also requires eye tracking to work since the illusion only works from a certain perspective.
These are not, of course, technically holograms. That’s actually an advantage in some cases because holograms require a tremendous amount of data that increases rapidly as the size of a display scales up. The optical trap display uses a much more manageable data rate.
We are big fans of POV displays, particularly ones that move into 3D. To do so, they need to move even faster than their 2D cousins. [danfoisy] built a volumetric display that doesn’t move LEDs or any other digital display through space, or project light onto a moving surface. All that moves here is a bead of styrofoam and does so at up to 1 meter per second. Having low mass certainly helps when trying to hit the brakes, but we’re getting ahead of ourselves.
[danfoisy] and son built an acoustic levitator kit from [PhysicsGirl] which inspired the youngster’s science fair project on sound. See the video by [PhysicsGirl] for an explanation of levitation in a standing wave. [danfoisy] happened upon a paper in the Journal Nature about a volumetric display that expanded this one-dimensional standing wave into three dimensions. The paper described using a phased array of ultrasonic transducers, each with a 40 kHz waveform.
After reading the paper and determining how to recreate the experiment, [danfoisy] built a 2D simulation and then another in 3D to validate the approach. We are impressed with the level of physics and programming on display, and that the same code carried through to the build.
[danfoisy] didn’t stop with the simulations, designing and building control boards for each 100 x 100 10 x 10 grid of transducers. Each grid is driven by 2 Intel Cyclone FPGAs and all are fed 3D shapes by a Raspberry Pi Zero W. The volume of the display is 100 mm x 100 mm x 145mm and the positioning of the foam ball is accurate down to .01 mm though currently there is considerable distortion in the positioning.
Check out the video after the break to see the process of simulating, designing, and testing the display. There are a number of tips along the way, including how to test for the polarity of the transducers and the use of a Python script to place the grids of transducers and drivers in KiCad.
The trick of a volumetric display is the ability to add a third dimension for positioning pixels. Here [Sean] delivered that ability with a stack up of ten screens to add a depth element. This is not such an easy trick. These small OLED displays are all over the place but they share a common element: a dark background over which the pixels appear. [Sean] has gotten his hands on some transparent OLED panels and with some Duck-Duck-Go-Fu we think it’s probably a Crystalfontz 128×56 display. Why is it we don’t see more of these? Anyone know if it’s possible to remove the backing from other OLED displays to get here. (Let us know in the comments.)
The rest of the built is fairly straight-forward with a Feather M4 board driving the ten screens via SPI, and an MPU-6050 IMU for motion input. The form factor lends an aesthetic of an augmented reality device and the production approach for the video puts this in a Bladerunner or Johnny Mnemonic universe. Kudos for expanding the awesome of the build with an implied backstory!
Volumetric 3D displays that allow the viewing of full 3D images without special glasses are not unknown in our community, usually taking the form of either a 3D LED matrix or a spinning rotor either with an image projected onto it or holding an LED array. They are impressive projects, but they are often limited in what they can display. Pretty patterns and simple 3D models are all very well, but they are hardly 3D television. Thus we’re quite impressed with [Evlmnkey]’s bachelor’s degree project, which combines motion capture and a volumetric display for a genuine volumetric 3D closed-circuit television system.
Finding the details takes a bit of dredging through the Reddit thread, but the display is an off-the-shelf Adafruit single-sided LED matrix driven by an ESP32, all mounted on a motor with a pair of slip rings for power. Data is fed to the ESP via WiFi, with the PC responsible for grabbing the image sending it as uncompressed frames. There’s little detail on the 3D capture, but since he mentions a Kinect library we suspect that may be the source.
This is perhaps not the highest resolution TV you’ll ever have seen, indeed we’d liken it to the flickering 30 lines of 1930s mechanical TV, but it’s still a functioning volumetric 3D live CCTV system. If you’re interested by 3D displays, you might like to see our examination of the subject.
We’ve seen 3D image projection tried in a variety of different ways, but this is a new one to us. This volumetric display by Interact Lab of the University of Sussex creates a 3D image by projecting light onto a tiny foam ball, which zips around in the air fast enough to create a persistence of vision effect. (Video, embedded below.) How is this achieved? With a large array of ultrasonic transducers, performing what researchers call ‘acoustic trapping’.
This is the same principle behind acoustic levitation devices which demonstrate how lightweight objects (like tiny polystyrene foam balls) can be made to defy gravity. But this 3D display is capable of not only moving the object in 3D space, but doing so at a high enough speed and with enough control to produce a persistence of vision effect. The abstract for their (as yet unreleased) paper claims the trapped ball can be moved at speeds of up to several meters per second.
It has a few other tricks up its sleeve, too. The array is capable of simultaneously creating sounds as well as providing a limited form of tactile feedback by letting a user touch areas of high and low air pressure created by the transducers. These areas can’t be the same ones being occupied by the speeding ball, of course, but it’s a neat trick. Check out the video below for a demonstration. Continue reading “Behold A 3D Display, Thanks To A Speeding Foam Ball”→
If you are a fan of sci-fi shows you’ll be used to volumetric 3D displays as something that’s going to be really awesome at some distant point in the future. It’s been about forty years since a virtual 3D [Princess Leia] was projected to Star Wars fans from [R2D2]’s not-quite-a-belly-button, while in the real world it’s still a technology with some way to go. We’ve seen LED cubes, spinning arrays, and lasers projected onto spinning disks, but nothing yet to give us that Wow! signaling that the technology has truly arrived.
We are starting to see these displays move from the high-end research lab into the realm of hackers and makers though, and the project we have for you here is a fantastic example. [Balduin Dettling] has created a spinning LED display using multiple sticks of addressable LEDs mounted on a rotor, and driven by a Teensy 3.1. What makes this all the more remarkable is that he’s a secondary school student at a Gymnasium school in Germany (think British grammar school or American prep school).
There are 480 LEDs in his display, and he addresses them through TLC5927 shift registers. Synchronisation is provided by a Hall-effect sensor and magnet to detect the start of each rotation, and the Teensy adjusts its pixel rate based on that timing. He’s provided extremely comprehensive documentation with code and construction details in the GitHub repository, including a whitepaper in English worth digging into. He also posted the two videos we’ve given you below the break.
What were you building in High School? Did it involve circuit design, mechanical fabrication, firmware, and documentation? This is an impressive set of skills for such a young hacker, and the type of education we like to see available to those interested in a career in engineering.