I've been looking online at some examples of AVR's that drive those 7 segment numeric LED's. I noticed that in the 2 or 3 digit models that they are driving the LED's all from the same pins and then using a transistor on each one hooked to a pin.
My theory is that they constantly rotate through the digits, displaying each one for a brief time.
My question is - can you tell that only one is being active at a time? Can you see a pulsing or strobing on them?
Also, is there any sort of issue when switching from one digit to the next - can the AVR change the 7 pins for the new digit and the 3 pins controlling the transistors all at exactly the same time? Or does it happen so fast that you can't see the led's change from one digit to another?
Does this affect the brightness of the LED's?
How many digits can be handled with this technique?