A mix of useful and useless information here. Many thanks to those who spent their time to come up with the former and address the actual question. The latter apparently came from people who have hard time controlling their temper.
Some remarks here:
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Nobody is arguing with the fact that the device is referred to as "multiplexed display". Why some people are trying to present it here as if it is a matter of debate is puzzling me. My post #3 contains a clear and concise explanation how the term "mutiplexing" got into the name of this device. If there is something that I haven't made sufficiently clear there - feel free to ask.
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References to how "hardware people" call it are interesting, but add little to the discussion. We are all aware of many remarkable peculiarities in the genesis of everyday technical terminology, ranging from ingenious to ridiculous. (I surely hope they don't use the term "multiplexing" to refer to the image-forming principle in a CRT display...) Also, see 1.
Some specific remarks:
Grumpy_Mike:
Yes it has. It is the term used by hardware people, it is the term everybody uses. Get used to not being correct when you wander outside your area of knowledge.
Please, refrain from such remarks about people whose "area of knowledge" you know nothing about. I'm inclined to let it slide this time. But keep in mind that we don't appreciate it here.
GolamMostafa:
The 'scanning technique' does not create the 'illusion' for us to see all the digits simultaneously; rather, it is the 'eye perception' by virtue of which we see that all the digits are there.
Um... Every time human perceptual system distorts one's perception of some natural phenomenon, it is called an illusion. In the above quote you begin by stating that it is not an illusion, and then right away proceed to show that it is.
I'd also use this opportunity to recommend R.L.Gregory's "Eye and Brain: The Psychology of Seeing" as a very good book that explains how many perceptive phenomena are actually facilitated by visual processing centers in human brain, not by human eye per se. This, BTW, also applies to our ability to form a complete image from its components presented by a "swept" display.
Grumpy_Mike:
Montmorency:
However, this has nothing to do with the need to constantly "sweep" the image on the display. The MF shield could, for example, implement simple latches for each segment in each digit to make it stay on by itself once it is lit (i.e. add internal "memory" for each segment). This would eliminate the need to constantly "sweep" the display. The display would simply hold its last set state for all its segments. Of course, such display would cost quite a bit more.All this is true except that when you implement what you describe here, you no longer have a multiplexed display.
And that's why I made this example. Note that the device might no longer be referred as "multiplexed display" by those "technical people" (BTW, are you sure about that?), but it would still rely on classic multiplexing for interface purposes. Another example would be a good old mechanical flip-disc display: such displays are controlled by a multiplexed data interface, yet they do not need to be constantly "swept" to maintain a continuous image.
These examples clearly show where the actual multiplexing begins and where it ends.
PaulRB:
As Paul__B already pointed out, there are no current limiting resistors for the led segments, and no transistors to boost the current for the display's common pins.
Good point about resistors, but the part about transistors is irrelevant. The transistors are normally needed to avoid overloading Arduino outputs when they are connected directly to the LED segments. However the display on this MF shield is not driven directly by Arduino, it is driven by a pair of MC74HC595AD registers, which can handle the load. Meanwhile, the Arduino only supplies data through a 3-wire multiplexed line.