I would like to wish my readers a Happy New Year and may all your wishes come true. As you may have experienced, during the holidays, hobbyists get some free time and they like spending it building stuff. In this case the author, Infernoz, build this 8 LED POV display, which seems like a fun way of wishing a happy new year. The device is based on the Attiny26 from ATMEL and from the video we can see it works quite nice, but unfortunately I was unable to locate any source code posted on the project page, but this is not that bad as you can find POV source code from others projects(POV1POV2POV3) if you’re interested in building one.
A persistence of vision (POV) display is a device that creates an apparently still image using rotating LEDs with great speed. The human eye is not able to distinguish every image individually, so the picture formed appears as a solid image. The POV phenomenon is not a new discovery and a lot of POV display projects have been made. However, this one right here has two different attributes that differentiate it from other POV displays: it is located on a fan placed on a ceiling and it’s silent.
This project uses a fan with 5 propeller blades and every blade has 32 LEDs mounted on it (that means a total of 160). These LEDs are connected to an Atmel microcontroller on an Arduino board. The POV display also uses 74HC595 8-bit serial-in, parallel-out shift registers that convert serial-in data into parallel-out data. The microcontroller generates the sequence in which the LEDs are lit, thus creating the image.
The location of the display makes it pretty cool and the fact that it’s attached to this kind of fan makes the whole device completely silent, which is quite different from most POV displays out there that are rather noisy. Having a thing like this blinking in your living room might seem like a good idea if you want to impress a guest audience, but other than that I can’t find a reason for actually using it.
When POVs first appeared in advertising panels i used to wonder how are the characters diplayed. Seemed like magic. Later on i found out its because of our eyes’ inertia. Where you needed a large number of LEDs to display a message, now you just need to spin a few LEDs. The rotation speed must be fast enough to display at least 10 frames per second, complex graphics may require a higher value between 15 and 30 fps, movies usually have between 24 and 30 fps.
This project will show you with great details how to build such a device. It is not an easy build, it takes a fair amount of tweaking to get it to work but the results can be spectacular. The developers of this project decided on a modular design, putting an emphasis on interactivity. In the end they came up with a very customizable POV that can display images you upload wirelessly and that you can manage in real time.
The microcontroller used is the Atmega644, leds are driven with the MAX6971 IC and Xbee modules provide the wireless serial communication between the POV and the PC from which you upload the image. A GUI written in Java makes this task easy for you.
The LEDs are place on a different PCB than the rest of electronics, this way it can be easily upgraded to a 3D version. The motor part needs some attention because you will have to carefully balance the LED board, you will deal with a lot of vibrations and the speed of rotation can be quite dangerous. Also there will be some tweaking involved when you will build the brushing system to power up the LEDs.
The motor has a separate power supply so that the main PCB won’t pick up noise. A HALL sensor is used to count the rotations and give the position of the LED board. When real time management of the display is not desired, the POV can use the picture stored in its EEPROM.
In order to power it, you will need a 9v power adapter that can deliver at least 1.1A for the electronics boards. Since the motor is powered from different source, you will need to meet your motor’s requirments. The one used in the project had its own 5V/2.5A power supply.
The cost for building this project is a little higher than 50$ and you can further reduce that if you already have some of the needed parts . All schematics and code are found in the project, below you can see the POV in action.
In one of my previous post I presented a simpe handheld POV device, it was a little bulky not really suited for a true handheld device. If you are interested of building a similar gadget this is the thing you need, small enough to be mounted under your wrist watch and has a mercury switch to synchronize the display to the movement.
The entire project is open hardware, even the gerber files are available, very nice indeed. Although the pcb’s will be hard to replicate because of the small size and smd components, but not impossible.
My choice would be to redesign the pcb for an ankle mounted POV, that way the pcb could get bigger, there will be room for larger batteries, and if you make two of them you can use it instead of ankle weights when jogging or at fitness trainings.
The term POV is for Persistance of Vision, I don’t want to bore you with definitions or explications, just look at the next picture:
The project is very simple, first of all because this type of display is the easiest to build, and because the author made it only for three letters, this way everybody can understand the basic principles and extend the functionalities.
The source code should be optimized and added some position sensing to synchronize the image. The schematic isn’t available but form the source code is easy to reverse engineer, since each led is driven from one micro controller pin.
If you add an accelerometer then you can stabilize the image even when rotating by hand, off course the overall weight must be reduced. With some wireless link you could even refresh the image dynamically.