ElectroMechanical Billboard Display

See link for details of a "flip clock" digit-display unit.

The starting-point Idea here is, instead of displaying a square with a digit on it, we display a square with a color on it, such as yellow or black or blue or white.... Depending on just how many "flaps" can be mounted on the mechanical wheel at the heart of the device, we could have quite an assortment of colors available. (Also see the "Rolodex" link.)

Note that in many clock mechanisms it is typical for digits to be connected to each other by gears, so that one full rotation of one digit-wheel causes one incremental partial rotation of the next wheel. We don't want that here. Instead we want each of these color-display units to have a "stepper motor" (see link) built into it. One electrical pulse through the unit's control-wires causes one incrementation, and displays the next color in the available sequence.

We now take many thousands of these display units and mount them next to each other as closely as possible, covering the surface of a billboard with them. This is the part that makes this Idea half-baked. Consider a largish billboard 10 meters long by 5 meters high, and suppose each "pixel" unit fits in 1 square centimeter. That's 500,000 pixel units to buy!

Note that these pixels are significantly larger than the pixels of an ordinary printed billboard image. However, because more colors are available for each pixel here, it is less important for the eye to be able to merge neighboring pixels to see a combined color. It means that the larger pixels of this billboard can still produce a good-quality large image.

We connect all their control wires to a computer. Something known as "multiplexing" (see link) makes this task less formidable than you might at first think. Note that if a factory makes 1-square-meter modular panels, each containing 10000 pixel units and an appropriate demultiplexer, the task of assembling the overall billboard becomes somewhat easier.

Those panels will likely be fairly heavy, so perhaps a smaller size (say 32 pixels square or 1024 per panel) might be better. Binary counting also makes demultiplexing more logical, even if it means the overall large billboard won't be an exact number of whole meters tall or wide. There are always trade-offs!

The computer is programmed to know which color is being displayed by each pixel unit in the billboard. The computer also knows the sequence of colors that will be displayed as the mechanical flaps are flipped by the stepper motor. Therefore it can figure how many stepper pulses are needed to change any pixel in this overall "display device" from one particular color to another.

Remember, this is a billboard, a device for displaying one image for a significant time. It is not intended for fast-motion video. But thanks to its computer control and the flexibility of its pixel units, the displayed image can be easily and fairly quickly changed, for the next static image (making it good competition for an ordinary billboard). And, of course, the computer can simply be turned off in-between image-changes, saving electricity, whenever an advertiser pays for a long-term display.