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Charlieplexing is a technique for driving a multiplexed display in which relatively few I/O pins on a microcontroller are used to drive an array of LEDs. The method uses the tri-state logic capabilities of microcontrollers in order to gain efficiency over traditional multiplexing. Although it is more efficient in its use of I/O, there are issues that cause it to be more complicated to design and render it impractical for larger displays. These issues include duty cycle, current requirements and the forward voltages of the LEDs. == Origination == Charlieplexing was proposed in early 1995 by Charlie Allen at Maxim Integrated.〔(maximintegrated.com )〕 The method, however, was known and utilized by various parties much earlier in the 1980s, and has been described in detail as early as in 1979 in a patent by Christopher W. Malinowski, Heinz Rinderle, and Martin Siegle of Department of Research and Development, AEG-Telefunken, Heilbronn, Germany for what they called a "three-state signaling system".〔http://www.google.com/patents/US4319227〕〔http://patentimages.storage.googleapis.com/pdfs/US4319227.pdf〕 ==Traditional multiplexing== Display multiplexing is very different from multiplexing used in data transmission, although it has the same basic principles. In display multiplexing, the data lines of the displays are connected in parallel to a common bus on the microcontroller. Then, the displays are turned on and addressed individually. This allows use of fewer I/O pins than it would normally take to drive the same number of displays directly. When using Charlieplexing, ''n'' drive pins can drive ''n'' digits with ''n'' − 1 segments. When simplified, it equates to ''n'' pins being able to drive ''n''2 − n segments or LEDs. Traditional multiplexing takes many more pins to drive the same number of LEDs; 2''n'' pins must be used to drive ''n''2 LEDs (though a 1-of-''n'' decoder chip can be used to reduce the number of microcontroller I/O pins to ). If the number of LEDs is known, then the previous equation can be worked backwards to determine the number of pins required. That is, ''L'' LEDs can be driven by pins. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Charlieplexing」の詳細全文を読む スポンサード リンク
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