Ingenious POV Business Card Waves Into Action with NeoPixels and a Simple Ball-Tilt Sensor
Microchip ATtiny85 measures the movement cadence to display POV messages on this business card.
Persistence of vision, or POV, creates the illusion of a two-dimensional image from a one-dimensional display element. A popular POV method is an array of LEDs attached to a movement arm. Asa Weiss, a mechanical engineer, took that concept and designed a POV business card that displays messages using NeoPixels and an eight-bit microcontroller when the person holding it shakes it back and forth.
Weiss created the POV Business Card several years ago. A recent contest brought it back into the light (or dark!). The initial version used discrete white LEDs connected to a Microchip ATtiny2313 8-bit microcontroller. However, this chip came in a relatively large 14-pin DIP package. The discrete LEDs meant Weiss had to solder them by hand to the microcontroller's pins individually.
The POV Business Card does not use a printed circuit board. Instead, it is a piece of acrylic with laser-engraved details. The engraving also provides a handy ruler for on-the-go measurements! A second revision replaced the white LEDs with a strip of RGB NeoPixels. A microcontroller drives these LEDs with a single pin using a serial-like protocol. Moving to the NeoPixels meant fewer pins needed, so Weiss replaced the microcontroller with a Microchip ATtiny85. These microcontrollers also come in a DIP package but are only eight pins.
A simple ball-tilt sensor provides the real magic behind the POV Business Card. As the user shakes the card back and forth, the sensor generates a signal that the microcontroller uses to determine the shake cadence and direction. This movement data allows the ATtiny85 to time the NeoPixels to generate a persistence-of-vision display. For example, it can show a name or graphic!
Check out this POV Business Card project write-up for more information about the design.