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The TV-B-Gone is an open source project by Adafruit and Mich Altman that stores all of the TV On/Off codes for virtually every brand of TV in the world. In short terms, it is a device that turns off TVs.
For more information on what it is, see the Wiki and Ladyada's site.

"Tired of all those LCD TVs everywhere?
Want a break from advertisements while you're trying to eat?
Want to zap screens from across the street?
The new Universal TV-B-Gone kit is what you need! This ultra-high-power version of the popular TV-B-Gone is fun to make and even more fun to use. "
Source: http://www.ladyada.net/make/tvbgone/index.html

Here is Ladyada's awesome TV-B-Gone website.
http://www.ladyada.net/make/tvbgone/index.html
It has great documentation on the build plus the schematic, firmware, and PCB in the Eagle format.

This is Adafruit's TV-B-Gone kit fully assembled.

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