Laser Projector Built From An Old Hard Drive

May 12, 2023 by Bryan Cockfield 41 Comments

Spinning hard drives are being phased out of most consumer-grade computers in favor of faster technology like solid-state drives and their various interfaces. But there’s still millions of them in circulation that will eventually get pulled from service — so what do we do with them? If you’ve got one that would otherwise be going in the garbage, they can be turned into some other interesting devices like this laser text projector.

Even the slowest drives spin at around 5000 RPM, which is perfect for this type of application. The device works by mounting twelve mirrors, each at a slightly different angle, on a drum which is spun by the drive’s motor. Bouncing a laser off of the spinning drum results in a projection of twelve horizontal lines. By rapidly switching the laser on and off depending on which mirror it’s pointing at, the length of each line can be controlled.

Thanks to persistence of vision, that allows you to show text on the surface that the laser is projected on. At speeds this high, it took [Ben] of Ben Makes Everything quite a few iterations to get it to a usable space. From sensors that were too slow to lasers not bright enough to 3D prints that were not accurate enough, he goes through the design of his build and the process in excellent detail.

After solving all of the problems including building his own constant-current laser power supply, and burning up a few laser diodes in the process, [Ben] has a laser projector capable of displaying readable text at a great distance which is also portable, running on a 12 V power supply. There are some possible areas of improvement that he notes as well, such as an unbalanced 3D printed part causing a bit of a wobble and the Arduino controller not being fast enough for more text. But it’s an impressive project nonetheless, similar to a two-mirror version we saw some time ago but with the ability to display text as well.

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A New Spin On 360 Degree Displays

July 21, 2021 by Michael Shaub 20 Comments

Back in 2018, [Salah] created a prototype display that seems to defy logic using little more than a Pringles can and a fast motor. While not volumetric, this hack does show the same 2D image from any vantage point in 360 degrees around it.

How can cardboard create this effect? Somewhat like a zoetrope uses slits to create a shutter effect, this display uses a thin slit to limit the view of the image within to one narrow vertical slice at a time. When moving fast enough, Persistence of Vision kicks in to assemble these slices into a complete image. What we think is so cool about this hack is that the effect is the same from any angle and by multiple viewers simultaneously.

The project page and video demonstration after the break are light on details, though the idea is so simple as to not require additional explanation. We assume the bright LED seen in the video below was added to overcome the relatively dim appearance of the image when viewed through the narrow slit and isn’t strictly required.

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3D Zoetrope Uses Illusion To Double The Frames

July 3, 2021 by Kristina Panos 10 Comments

Although film and animation have come quite a long way, there’s still something magical about that grandaddy of them all, the zoetrope. Thanks to persistence of vision, our eyes are fooled into seeing movement where there is none, only carefully laid-out still pictures strobing under the right lighting.

After four months of research, CAD, prototyping, and programming, [Harrison McIntyre] has built a 3D zoetrope that brings a gif to glorious physical life (video, embedded below). All the image pieces are printed and move under a fancy backlight that [Harrison] borrowed from work. It works essentially the same as a 2D zoetrope, as long as you get the spacing juuuuust right. 360° divided by 20 frames comes out to 18° per frame. So a motor spins the disk around, and every 18°, the light pulses for one millisecond and then turns off until the next frame is in position.

The really interesting thing is that there are actually more than 20 frames at play here. If you follow a single character through the loop, it takes 46 frames to complete the animation thanks to something 3D zoetrope pioneer [Kevin Holmes] dubbed ‘animation multiplexing‘, which in [Harrison]’s example, is easily explained as a relay race in which all runners run their section at the same time, creating the illusion of constant motion.

There’s more than one way to use a 3D printer to create a zoetrope, and we doubt we would have ever thought of this one that squashes four dimensions into three.

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Wiggling Screen And DLP Power This Volumetric POV Display

July 1, 2021 by Dan Maloney 25 Comments

It seems like the world is ready for a true 3D display. We’ve seen them in sci-fi for decades now, with the ability to view a scene from any angle and inspect it up close. They’ve remained elusive, but that might just be changing thanks to this open-source persistence-of-vision volumetric display.

If the VVD, as it has been named by its creator [Madaeon], looks somewhat familiar, perhaps it’s because editor-in-chief [Mike Szczys] ran into it back in 2019 at Maker Faire Rome. It looks like it has progressed quite a bit since then, but the basic idea is still the same. A thin, flexible membrane, which is stretched across a frame, is attached to articulated arms. The membrane can move up and down rapidly, fast enough that a 1,000-fps high-speed camera is needed to see it move. That allows you to see the magic in action; a digital light processor (DLP) module projects slices of a 3D image onto the sheet, sending the correct image out for each vertical position of the membrane. Carefully coordinating the images creates the POV illusion of a solid image floating in space, which can be observed from any angle, requires no special glasses, and can even be viewed by groups.

With displays like this, we’re used to issuing the caveat that “it no doubt looks better in person”, but we have to say in the GIFs and videos included the VVD looks pretty darn good. We think this is a natural for inclusion in the 2021 Hackaday Prize, and we’re pleased to see that it made it to the semi-finals of the “Rethink Displays” round.

Big Spinning Disk Makes A Small Color Video Display

June 23, 2021 by Donald Papp 6 Comments

Believe it or not, the Mickey Mouse clip used for this demonstration is actually in the public domain.

The earliest televisions used a spinning disk technology called the Nipkow disk, which is exactly what [Science ‘n’ Stuff] recreated with their Arduino-based mechanical color television (video link, also embedded below.) The device reads video and audio from an SD card, and displays the video using a precisely-timed RGB LED visible through a perforated spinning disk. The persistence of vision effect results in a video that is small, relative to the size of the disk, but perfectly watchable. A twist is that the video is in color!

A Nipkow disk is a fairly simple and electromechanical device that relies on timing; something a modern microcontroller and RGB LED is perfectly capable of delivering. In this device, the holes in the disk create 32 vertical scanlines with 96 “pixels” making up each of those lines. Spinning disk technology was always limited to being monochromatic, but in this implementation, each “pixel” is given its own unique color by adjusting the RGB LED accordingly.

The first video shows off the device and demonstrates it working; note that it may look like there are multiple little screens, but the center one can be thought of as the “true” display with the others essentially being artifacts due to light leakage. If you’re interested in the nuts and bolts of exactly how a Nipkow disk works, then the second video is what you’ll be more interested in, because it goes through all the details of exactly how everything functions.

Another neat thing about Nipkow disks is that image acquisition is really not much more complex than image display.

[via Arduino Blog]

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This POV Clock Combines A Nixie With A Pendulum

May 7, 2021 by Dan Maloney 6 Comments

Talk about your mixed timekeeping metaphors: there are clocks, and pendulum clocks, and there are Nixie clocks, and persistence of vision clocks. But this is a Nixie pendulum POV clock, and we think it’s pretty cool.

We first spied this on Twitter and were subsequently pleased to learn that [Jayzon Oeve] has posted a more detailed build log over on Hackaday.io. Rather than a moving array of dots to create the characters to display, this uses a single IN-12b Nixie tube at the end of a pendulum. The pendulum is kept moving by a small nudge created by a pulse through a fixed hard drive voice coil acting on a magnet affixed to the bottom of the pendulum — we’ve seen a similar approach used before.

Pretty much all of the electronics are mounted on the pendulum arm, including a Nano, an RTC, and an accelerometer to figure out where in the swing the bob is and when to flash a number on the display. There’s a video below that shows it at work both at full speed and in slow-motion; as always with POV clocks, these things probably look better in person than on video. And while swinging Nixies around like that seems a little dicey, we like the way this turned out.

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Motor-Driven Movement Modernizes POV Toy

February 24, 2021 by Kristina Panos 1 Comment

Just as we are driven today to watch gifs that get better with every loop, people 100+ years ago entertained themselves with various persistence of vision toys that used the power of optical illusions to make still images come to life. [jollifactory] recently recreated one of the first POV devices — the phenakistoscope — into a toy for our times.

The original phenakistoscopes were simple, but the effect they achieved was utterly amazing. Essentially a picture disk with a handle, the user would hold the handle with one hand and spin the disk with the other while looking in a mirror through slits in the disk. Unlike the phenakistoscopes of yore that could only be viewed by one person at a time, this one allows for group watching.

Here’s how it works: an Arduino Nano spins a BLDC motor from an old CD-ROM drive, and two strips of strobing LEDs provide the shutter effect needed to make the pictures look like a moving image.The motor speed is both variable and reversible so the animations can run in both directions.

To make the disks themselves, [jollifactory] printed some original phenakistiscopic artwork and adhered each one to a CD that conveniently snaps onto the motor spindle. Not all of the artwork looks good with a big hole in the middle, so [jollifactory] created a reusable base disk with an anti-slip mat on top to spin those.

If you just want to watch the thing in action, check out the first video below that is all demonstration. There be strobing lights ahead, so consider yourself warned. The second and third videos show [jollifactory] soldering up the custom PCB and building the acrylic stand.

There are plenty of modern ways to build old-fashioned POV toys, from all-digital to all-printable.

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