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The little disposable battery testers that you see on batteries or battery packages are a great example of combined technologies -- several existing technologies have been combined in a completely new way! Battery testers depend on two special types of ink: thermochromic and conductive inks. Thermochromic ink changes color depending on its temperature. Conductive ink can conduct electricity. By applying layers of these special inks along with a layer of normal ink using a fairly normal printing press, it is possible to create an extremely inexpensive printed design that changes depending on the amount of electricity it receives.

več na: http://electronics.howstuffworks.com/ev...

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