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Viewer assembly and operation
Google Cardboard headsets are built out of simple, low-cost components. The headset specifications were designed by Google, which made the list of parts, schematics, and assembly instructions freely available on their website, allowing people to assemble Cardboard themselves from readily available parts. Pre-manufactured viewers were only available from third-party vendors until February 2016, when Google began selling their own through the Google Store.The parts that make up a Cardboard viewer are a piece of cardboard cut into a precise shape, 45 mm focal length lenses, magnets or capacitive tape, a hook and loop fastener (such as Velcro), a rubber band, and an optional near field communication (NFC) tag. Google provides extra recommendations for large scale manufacturing, and pre-assembled kits based on these plans are available for less than US$5 from multiple vendors, who have also created a number of Cardboard variations.
Once the kit is assembled, a smartphone is inserted in the back of the device and held in place by the selected fastening device. A Google Cardboard–compatible app splits the smartphone display image into two, one for each eye, while also applying barrel distortion to each image to counter pincushion distortion from the lenses. The result is a stereoscopic (3D) image with a wide field of view.
The first version of Cardboard could fit phones with screens up to 5.7 inches (140 mm), and used magnets as input buttons, which required a compass sensor in the phone. An updated design released at Google I/O 2015 works with phones up to 6 inches (150 mm), and replaces the magnet switch with a conductive lever that triggers a touch event on the phone's screen for better compatibility across devices.
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