Quote Originally Posted by Melanie View Post
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There is a SECOND AND VERY BIG ADVANTAGE to this technique... if you want to display '1' or '8888' the current consumption will be the same (that for ONE segment - say 10mA). Go display '8888' on a quad 7-segment display using the usual amateurish sloppy techniques of switching all the segments ON that you want at the same time and tell me how much current you pull... (7 segments, multipled by the number of digits, multiplied by say 10mA for each segment...). 7 x 4 x 10mA = 280mA... I've had so many laughs at some of the schematics and coding that I've seen for 7-segment displays...
Hi Melanie,

I think your calculations are a bit off. The multiplexed 4-digit display you mention above would only have one digit lighted at a time and so if you were driving each segment at 10-ma while displaying "8888" you would only be drawing 70-ma total current (70-ma while displaying digit 1, 70-ma while displaying digit 2, and so on) and not the 280-ma you mentioned.

You seem to be ignoring "duty cycle" in your explanations. While the "one-at-a-time" method you mention would provide 10-ma total current draw the average current per LED in a 4-digit (28-segment) display would be only 1/28th of 10-ma or approximately 0.357-ma. By comparison, driving each segment of a multiplexed display at 10-ma at a 1/4th duty cycle would provide 2.5-ma average current per LED. Now as you've pointed out, painting "8888" on a 4-digit multiplexed display would cost 70-ma compared to 10-ma with the "one-at-a-time" method but you forgot to mention that the average current per LED is seven times higher which translates into a much brighter display.

Suggesting that a "one-segment-at-a-time" method or design is better than a multiplexed design based solely on the total current used is silly but it did provide me and several associates with a few giggles.

Kind regards, Mike