There were some 3-Digit LED displays lying around to play with. So i hooked it up to an Arduino for fun. There are 11 lines - one for the positive for each digit, and one corresponding to each segment. Thus, unless you want to display the same thing on all three digits, you must switch the configuration faster than about 60 Hz.
If hooked up directly, it uses up 11 lines of the Arduino. But with a 74595 shift register to expand the output, this can be reduced to 4. You still have to run a fairly tight loop switching the pins, so it kind of uses up the controller. On the other hand, this would easily run in a very small controller so it still might be useful.
The scope shows the serial line. The arduino is merely counting up every 100ms. Circuit and code to follow eventually. More coffee is needed first.