Persistence of Vision (POV) is a curious part of the human visual system. It’s the effect by which the perception of an image lingers after light has stopped entering the eye. It’s why a spinning propeller appears as a disc, and why a burning sparkler appears to leave a trail in the air. It’s also commonly used as a display technology, where a series of flashing LEDs can be used to create messages that appear to float in the air. POV displays are a popular microcontroller project, and today, we’ll explore the basic techniques and skills required in such builds.
This thing right here might be the coolest desk toy since Newton’s Cradle. It’s [Stephen Co]’s latest installment in a line of mesmerizing, zodiac-themed art lamps that started with the water-dancing Aquarius. All at once, it demonstrates standing waves, persistence of vision, and the stroboscopic effect. And the best part? You can stick your finger in it.
This intriguing lamp is designed to illustrate Pisces, that mythological pair of fish bound by string that represent Aphrodite and her son Eros’ escape from the clutches of Typhon. Here’s what is happening: two 5V DC motors, one running in reverse, are rotating a string at high speeds. The strobing LEDs turn the string into an array of optical illusions depending on the strobing rate, which is controlled with a potentiometer. A second pot sweeps through eleven preset patterns that vary the colors and visual effect. And of course, poking the string will cause interesting interruptions.
The stroboscopic effect hinges on the choice of LED. Those old standby 2812s don’t have a high enough max refresh rate, so [Stephen] sprung for APA102Cs, aka DotStars. Everything is controlled with an Arduino Nano clone. [Stephen] has an active Kickstarter campaign going for Pisces, and one of the rewards is the code and STL files. On the IO page for Pisces, [Stephen] walks us through the cost vs. consumer pricing breakdown.
Senior college projects are the culmination of years of theoretical learning finally put into practice. For many students they are their first experience of doing some proper, real world engineering. [Melangeaddict] chose to take on a persistence of vision display for his final project, and learned plenty along the way.
The display consists of a row of 48 RGB LEDs mounted on an arm capable of rotating a full 360 degrees, with a simple paper diffuser. This arm is spun up by a belt drive from an electric motor at significant rotational speed, so getting close to this machine is quite inadvisable. Thanks to quality bearings and a careful build, rotating resistance is minimal. An infrared LED is mounted on the frame, and the light picked up by a photodiode on the rotating arm, allowing the images to remain fixed in space without drifting over time. Images can be loaded to the display wirelessly over a Bluetooth interface, which was quite advanced for a DIY project in 2011.
We’re a fan of the 360 degree approach to POV displays, and with the right rotational speed and fast data rates, it would be possible to get some seriously high resolution out of the device. Just be careful not to stick your hands in the mechanism.
Persistence of vision is a fun feature of the human visual system, which allows us to blink a bunch of spinning LEDs at the right time to spell out messages that appear to hang in the air. [TN_Inventor] took a stab at his own POV build, using an old desk fan as a base.
The initial build relied on a rotor made of MDF and some very old-school LEDs. The rotor was heavy and unbalanced, causing issues for the motor, and the dim LEDs weren’t visible in normal daytime conditions. Like any good maker, [TN_Inventor] persevered and iterated the design.
The next revision instead relied on protoboard itself for the rotor, greatly reducing the weight and making it easier to balance. The problem of getting power to a rotating mechanism was sidestepped entirely, with a small lipo battery being mounted on the rotor itself. High-brightness white LEDs were employed, making the effect much more visible. This was helped further thanks to the use of transistors to run the LEDs directly from battery voltage, rather than obeying the current limits of the Arduino Nano’s output pins.
The build presents well, with the final POV board being built into the chassis of an old desk fan. Rather than use the original motor, instead a smaller 12 volt geared device was used, powered separately from the main board. The familiar form factor of the desk fan is a great way to finish the project off, and gives it an interesting industrial aesthetic.
POV builds can go a long way – we’ve even seen volumetric displays built in this way. Video after the break. Continue reading “Persistence Of Vision On An Old Fan”
By taking advantage of persistence in human vision, we can use modest bits of hardware to create an illusion of a far larger display. We’ve featured many POV projects here, but they are almost always an exploration in two dimensions. [Jamal-Ra-Davis] extends that into the third dimension with his Volumetric POV Display.
Having already built a 6x6x6 LED cube, [Jamal] wanted to make it bigger, but was not a fan of the amount of work it would take to grow the size of a three-dimensional array. To sidestep the exponential increase in effort required, he switched to using persistence of vision by spinning the light source and thereby multiplying its effect.
The current version has six arms stacked vertically, each of which presents eight individually addressable APA102 LEDs. When spinning, those 48 LEDs create a 3D display with an effective resolution of 60x8x6.
We saw an earlier iteration of this project a little over a year ago at Bay Area Maker Faire 2018. (A demo video from that evening can be found below.) It was set aside for a while but has now returned to active development as an entry to Hackaday Prize 2019. [Jamal-Ra-Davis] would like to evolve his prototype into something that can be sold as a kit, and all information has been made public so others can build upon this work.
[Bithead] wanted to make a prop replica of an Electrostaff from Star Wars, but wasn’t sure how best to create the “crackling arcs of energy” effect at the business ends. After a few false starts, he decided to leverage the persistence of vision effect by spinning LEDs in more than one axis to create helical arcs of light and it seems that this method has some potential.
Many multi-axis persistence of vision devices use a component called a slip ring in order to maintain electrical connections across rotating parts, but [Bithead] had a simpler plan: 3D print a frame and give each axis its own battery. No centralized power source means a quicker prototype without any specialized parts, and therefore a faster proof of concept to test the idea.
[Bithead] already has improvements planned for a new version, but you can see the current prototype in action in the short video embedded after the break.
The 2019 Hackaday Prize, which was announced last week, is very much on everyone’s mind, so much so that we’ve already gotten a great response with a lot of really promising early entries. As much as we love that, the Prize isn’t the only show in town, and we’d be remiss to not call attention to our other ongoing contest: The Flexible PCB Contest.
The idea of the Flexible PCB Contest is simple: design something that needs a flexible PCB. That’s it. Whether it’s a wearable, a sensor, or a mechanism that needs to transmit power and control between two or more moving elements, if a flexible PCB solves a problem, we want to know about it.
We’ve teamed up with Digi-Key for this contest, and 60 winners will receive free fabrication of three copies of their flexible PCB design, manufactured through the expertise of OSH Park. And here’s the beauty part: all you need is an idea! No prototype is necessary. Just come up with an idea and let us know about it. Maybe you have a full schematic, or just a simple Fritzing project. Heck, even a block diagram will do. Whatever your idea is for a flexible PCB project, we want to see it.
To get the creative juices going, here’s a look at a few of the current entries
The Flexible PCB Contest goes through May 29, so you’ve got plenty of time to get an idea together.