Persistence of vision (or POV) is the phenomenon by which the eye, seeing a rapidly moving objects, stitches together the object’s position at different times into a single cohesive image. This phenomenon is leveraged by CRT displays, which use raster scanning to draw individual pixels in each horizontal scanline before returning to the beginning of the next one. In contrast, our spherical display displays scanlines vertically. We have built a spherical display that creates a picture by rapidly alternating the colors displayed by each of a column of LED pixels. Each column of vertical pixels displays simultaneously. The physical location of the light source is then moved by a short distance before the subsequent vertical scanline is displayed.
Our system consisted of a 60-pixel LED strip mounted on an acrylic ring, which was lined with a 60-pixel LED strip running an array of LED pixels. Its bottom is mounted to a 6V DC motor with an encoder which uses a Hall-effect sensor to accurately determine its position. The motor’s rotational velocity is set to 500 rpm. A 6-wire slip ring from Adafruit allowed us to connect the LED power, clock, and data lines from a stationary frame to the rotating acrylic ring. (Since 6 wires are available, 2 wires each are used for power and ground lines.)
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