Wheel Position SensorAs described earlier, raw wide angle and stereo photos must be processed in order to remove their characteristic distortions. Bulgy-looking wide angle photos need to be transformed into a wide rectangular shape, while raw stereo pairs need to be merged into 3D anaglyphs. During processing, the Bigshot software must distinguish between the types of photos being processed so that it applies the appropriate transformations. The wheel position sensor, a pair of mechanical switches located behind the polyoptic wheel, makes distinguishing between the types of photos possible. Its switches get turned on or off depending on the wheel's current setting (its rotated position).
Figure 7 shows a position sensor for a wheel that has four optical modules, which are labeled 0 to 3. The module that is currently being used is highlighted in red. Rotating the wheel causes different triggers (dark gray bumps) to fall in place underneath the switches (empty red circles), activating the switches. The position of the wheel (that is, the module being used) is determined by the switch that is activated. Bigshot's electronics label each photo that is taken with its corresponding type (normal, wide angle, or stereo) by seeing which switch was active when the photo was taken. The design in Figure 7 is not very efficient, however. It uses four switches to read the wheel's position when only two switches are required, as Figure 8 shows:
The difference with Figure 8's design is that a combination of switches are read to find the wheel's position rather than a single switch. When a switch is activated, it is represented by the number 1, and when it is not activated, it is represented by the number 0. By reading all of the switches, the electronics are ultimately reading a combination of 1's and 0's, known as a binary sequence [1]. The placement of the triggers assigns each optical module with a unique combination that acts as the passcode for that module. By comparing the combination of 1's and 0's that are read from the switches with the passcodes for each of the optical modules, Bigshot's electronics can determine the module that is currently being used. Note that Figure 8 uses just two switches to identify four optical modules. In general, a wheel position sensor can identify up to 2N modules using just N switches. For example, the wheel position sensor in Figure 9 can identify 16 different modules using only four switches.
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