Persistence Of Vision Death Star

Death Stars were destroyed twice in the Star Wars movies and yet one still lives on in this 168 LED persistence of vision globe made by an MEng group at the University of Leeds in the UK. While Death Stars are in high demand, they mounted it on an axis tilted 23.4° (the same as the Earth) so that they can show the Earth overlaid with weather information, the ISS position, or a world clock.

More details are available on their system overview page but briefly: rotating inside and mounted on the axis is a Raspberry Pi sending either video or still images through its HDMI port to a custom made FPGA-based HDMI decoder board.  That board then controls 14 LED driver boards mounted on a well-balanced aluminum ring. All that requires 75W which is passed through a four-phase commutator. Rotation speed is 300 RPM with a frame rate of 10 FPS and as you can see in the videos below, it works quite well.

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Bending the Light

Ruled Hyperboloid CC Prof. William McCallum
Ruled Hyperboloid CC Prof. William McCallum

Everyone knows you can’t visibly bend light over short distances in free air. Or can you? [Jack Pearse] has figured out a way to do it though, or at least make it appear that way. He does it by combining a trick of math and a trick of the eye. The secret is the hyperboloid, a geometric construct described by a quadratic equation. [Jack’s] creation is more specifically a hyperboloid in one sheet. This type of structure allows straight lines to create a an overall curved surface.  Hyperboloids have been used by architects and in construction for years, often in tall structures like water towers.

If a bunch of straight steel beams can form a curved shape, lasers should be able to pull off the same effect. By employing persistence of vision, [Jack] was able to create his hyperboloid with only 10 small lasers. The lasers are mounted on the rim of a bicycle wheel and carefully aimed. The wheel is spun up with using an electric bicycle motor. [Jack] kept things safe by building a centrifugal switch. The switch powers up all the lasers in when the tire is spinning. This ensures no one can be hit by a static beam.

Once the wheel is spinning, all you need is a bit of smoke or haze in the room. The spinning lasers combine to form the hyperboloid shape. You can see the project in action in the video after the break.

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Wooing A Lady Into Persisting with Persistence… of Vision

As the story goes, years ago [Matt Evans] was wooing the beautiful and talented [Jen]. There were many suitors vying for her hand; he would have to set himself apart. The trouble was, how to convince her that persisting in the relationship was the best and only course? What did he have to offer? Of course many of us know the answer; having wooed our own significant others with the same thing. Incredible and unrepentant nerdiness.

So! He toiled late into the night, his eyes burning with love and from the fumes of solder smoke. For her he would put his wizardry to work. At the wave of a hand would write songs of adoration in the air with nothing but light. The runes of power, all typed out in the proper order, would be held by a ATiny. A CR2032 coin cell provided the magic pixies which would march to its commands, delivering their spark to the LEDs in the right order.

He etched the board, wrote the code, and soldered the components. He encased it in his finest box of crystal clear plastic and black static foam, a gift of the samples department of the Maxim corporation.

Presumably the full moon was high in the air when he presented the box. He took it out and waved it with a flair. Poetry floated there in front of her eyes. It read, “Jen is cool!”. A few years later, they were married.

Blinktronicator’s POV Sends Our Eyebrows Rocketing Skyward

You think you’ve seen everything that there is to see regarding blinking LEDs and then a simple little trick proves you wrong. Our friend [Zach Fredin], aka [Zakqwy], added a pander mode to his blinky board which shows the Hackaday Jolly Wrencher in a Persistence of Vision mode. We love pandering, and obviously you just need to start the mode and wave the board back and forth. But in thinking the obvious you’d be wrong.

Badass deadbug soldering to “fix” a mirrored shift register footprint

In the video after the break [Zach] demonstrates all the features of the blinktronicator and it’s recently finalized firmware. The tiny little board is a USB dongle featuring two buttons and an arc of sixteen LEDs in a rainbow of colors. When we say tiny, we mean it. Those LEDs are 0402 components and the board was small enough (and interesting enough) to receive an honorable mention in the Square Inch Project.

You would think that soldering all those LEDs by hand would be the trick, but [Zach] pulled off a much more difficult feat. Look closely at the image here (or click to embiggen). The two shift register footprints on the prototype were mirrored. He deadbug soldered each of them using — get this — the individual strands from some 28 AWG stranded wire. You sir, get the hardcore hand soldering badge and then some.

Okay, we’ll stop beating around the bush. The ATtiny45 on this board isn’t connected to the USB data lines, they’re only for power. That means, at its heart this is purely a blinking LED project, albeit one that uses the huge range of colors of the PICOLED family of parts. [Zach] did well with just two user inputs, but it’s the very simple POV party trick that really sucked us in. Instead of waving the board around, [Zach] uses a metal offset spatula as a mirror. Moving it back and forth unfolds the carefully timed flashes to draw your message in the air. Such a simple concept, but so satisfying to see it applied in a slightly different way.

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Disk Hack Creates Persistence of Vision

[Adam Antok] was compelled to create this repurposed hard drive persistence of vision hack after seeing a toy of the same nature.

hdd-display-schematicHe used the frame, disk and motor from a drive and added LEDs under the spinning disk as the light source. The disk has 8 small holes drilled equidistant around the disk, and spiraling slightly toward the center. As the holes pass by the LEDS they are flashed by the ATtiny2313 processor to create images. To determine the position of the platters a Hall effect sensor is monitored by the 2313 to detect a magnet on the underside of the disk. There is room to display ten characters at one time. Each cursor position can scroll through the character set by rotating an encoder. For all the precision needed to coordinate the LEDs with the spinning holes the electronics and software code are amazingly simple. That’s a really nice job, [Adam]!

Persistence of vision hacks are to hackers like flames are to moths. One really nice thing about [Adam’s] project is that you can interact with it while it’s running. Check it out after the break.

For a novel take on POV, check out this slow swinging pendulum clock.

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Hacklet 32 – LED Persistence of Vision Displays

Blinking LEDs are good. Moving, spinning things are good too. Put them both together and you get a Persistence of Vision (POV) display. Hackers have been building these displays for years. This week’s Hacklet focuses on some of the best LED POV displays on!

povtypeWe start with [EduardoZola] and POV as you type, write on the air. [Eduardo] used an Arduino Nano, a pair of 433 MHz radios, some blue LEDs and a motor to create a simple spinning display. A hall effect sensor keeps everything in sync. The entire display is powered by a 500 mAh LiPo battery. The awesome thing about this display is the interactive aspect. The transmitter module connects to a laptop via an on-board USB to serial converter. Typing into any serial terminal sends the text directly to the POV display, where the letters appear to hang in the air.


deathringNext up is [boolean] with Silent Orchestra POV aka “Death Ring”. [boolean] didn’t want to just create a POV ring, he wanted a huge 5 foot diameter display for his local Burning Man decompression. Death Ring is an aluminum ring spun by a 3HP motor. A hall effect sensor keeps everything synced up, and keeps Death Ring’s 3 horsepower motor in check. Light is provided by a PixelPusher and WS2812 RGB strips. The system is designed to be interactive, controlled with a Leap Motion controller or a Microsoft Kinect. An MPU-6050 keeps acceleration in check while processing maps video to the LED strip. An Arduino Yun allows the entire system to be controlled via WiFi. [boolean] and his team have taken Death Ring through several revisions. Judging by the quality of their aluminum welding though, they’re on the right track to an awesome end result! power user [Davedarko] has been working on a POV display of a different sort. His Locomatrix is an 8×8 LED matrix which moves in and out on the Z axis. [Dave] originally created Locomatrix as his entry in the 2014 Hackaday Prize. We have to admit this is the first time we’ve seen this sort of display, but the idea is sound. In fact, [Bruce Land] posted in the comments to let [Dave] know that he’d seen a similar technique used with a CRT display back in 1964. We’re betting Dave’s 3D printed gears and LED matrix display will be more robust than a CRT tube slamming two and fro at several hundred pulses per minute!

CPOVFinally, we have Hackaday’s own [Mike Szczys] with CPOV – a Crappy Persistence of Vision display . CPOV is a proof of concept made from upcycled parts which [Mike] threw together in a couple of hours. He grabbed the motor from an old cassette deck, some plywood, perfboard, and of course LEDs to build his display. The processor is an ATtiny2313 running Adafruit’s MiniPOV 3 firmware. The system display doesn’t have a sync input, so [Mike] uses a novel form of Human-in-the-loop PWM control to keep the motor speed in check. CPOV is proof that isn’t just for polished projects, but for proof of concepts, fails, and just plain research. Even if your project isn’t perfect, documenting it will help you learn from it. It might even inspire someone else to move forward and continue where you left off!

Want more POV goodness? Check out our new POV display list!

Our LEDs are going dim, so that’s about all the time we have for this Hacklet. As always, see you next week. Same hack time, same hack channel, bringing you the best of!

Arduino Tetris on a Multiplexed LED Matrix

[Alex] needed a project for his microcomputer circuits class. He wanted something that would challenge him on both the electronics side of things, as well as the programming side. He ended up designing an 8 by 16 grid of LED’s that was turned into a game of Tetris.

He arranged all 128 LED’s into the grid on a piece of perfboard. All of the anodes were bent over and connected together into rows of 8 LED’s. The cathodes were bent perpendicularly and forms columns of 16 LED’s. This way, if power is applied to one row and a single column is grounded, one LED will light up at the intersection. This method only works reliably to light up a single LED at a time. With that in mind, [Alex] needed to have a very high “refresh rate” for his display. He only ever lights up one LED at a time, but he scans through the 128 LED’s so fast that persistence of vision prevents you from noticing. To the human eye, it looks like multiple LED’s are lit up simultaneously.

[Alex] planned to use an Arduino to control this display, but it doesn’t have enough outputs on its own to control all of those lights. He ended up using multiple 74138 decoder/multiplexer IC’s to control the LED’s. Since the columns have inverted outputs, he couldn’t just hook them straight up to the LED’s. Instead he had to run the signals through a set of PNP transistors to flip the logic. This setup allowed [Alex] to control all 128 LED’s with just seven bits, but it was too slow for him.

His solution was to control the multiplexers with counter IC’s. The Arduino can just increment the counter up to the appropriate LED. The Arduino then controls the state of the LED using the active high enable line from the column multiplexer chip.

[Alex] wanted more than just a static image to show off on his new display, so he programmed in a version of Tetris. The controller is just a piece of perfboard with four push buttons. He had to work out all of the programming to ensure the game ran smoothly while properly updating the screen and simultaneously reading the controller for new input. All of this ran on the Arduino.

Can’t get enough Tetris hacks? Try these on for size.