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MAKE subscriber Florin points out this thorough rundown on 7-segment display usage, even covering the basics of multiplexing with the common component –

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Since the digits share the same data bus, each digit will have the same number displayed, like the wheel on the picture, to change the number the “data guy” rotates the wheel. So how can we display 1234 you might ask, well wee need another guy, the selector, which will leave only one digit to be seen, all the others are shut off, by synchronizing the “data guy” and the “selector guy ” so they operate at the same time, when the wheel is at the 1111 position, the selector opens the first window, when at 2222 it opens the second and so on. By changing the data and selecting the digits at many times per second the human eye will see a steady image with 1234, the display refresh rate should be above 50 times in 1 second, otherwise the image may flicker.

Whether you consider yourself a “data” or “selector guy” (or gal), the tutorial seems handy way to get acquainted with such concepts.