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English: This is an image of a clock I designed, built and photographed entirely myself which uses Charlieplexing (though I did not know I was only reproducing someone else's display method, I thought I was inventing it for the first time) - Note that there are 90 LEDs used exactly (you must count the LED in the center twice as it is a bicolor LED, green for AM and red for PM), which are controlled by 10 I/O pins of a PIC16C54 microcontroller, and that is the fundamental limit to the number of LEDs that can be controlled by that number of pins through Charlieplexing. Also note there are 2 input switches and an additional output to a speaker for the alarm, so the entire device uses 13 I/O pins, the total amount possessed by the PIC16C54, so it would in fact be impossible to add a single additional LED to this clock without sacrificing an input or the speaker output or requiring additional chips such as D flip-flops to demultiplex. As of this writing, this particular clock hangs on the office wall of Clayton Price, head of undergraduate administration for the Computer Science department of the Missouri University of Science and Technology. The writing to the right of the word "set" which is on the threshold of legibility at this resolution reads "Clock if other button is not pressed" followed by "alarm if other button is pressed".
|Date||22 October 2003|
Clock information as well as kit is available from medexamtools.com
Creative Commons Attribution 3.0 Unported
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