Steve:
Ok Ok I give in. My comments were really aimed at the participants that come to this forum and ask "How do I make an 8052 light my LED? I think that in most cases the guys and gals designing massive LED lanels, multi-segment LED displays like Time/Temp displays on signs, and similar applications will fit into the category of "those that need a more sophisticated solution" that I mentioned in my previous posting. Be that as it may, I don't deny that a small micro system powered off say 3.3 volts with a LDO series regulator off a raw 6 volt supply rail should drive its LEDs off the 3.3 volts. But please also consider that there are also loads of designs that are using regulated bricks to power circuitry directly without any intermediate on-board regulators. In these any LEDs are most likely driven off the "Vcc" line directly.

There is actually nothing wrong with Chris including two stage circuits in his tutorial if he should so choose. But getting back to my argument about which voltage is used to drive them one comes back to the same thing again. If you are going to be driving dozens or 100's of LEDs it is extremely unlikely that it will be suitable or even desireable to drive all those LEDs with dual tranistor circuits with all the attendant descrete resistors to go with them. Instead you are going to look for driver chips of some sort with 8, 16 or more outputs or your going to look at matrix multiplex systems where you pound the LEDs with huge current levels. So back to my general issue....if you have a few, like 1, 2, maybe even 5 LEDs in a design then it is mostly plausable to drive them off the same supply as the microcontroller and use a simple single transistor circuit.

Michael Karas