Foy -
I'm really happy that I'm able to enhance your understandings of things. It truly does make me as happy to teach as it does to learn -- and I love to learn.
Part of the reason that this build is as complicated as it is lies in the fact that I'm using a very high performance switching regulation scheme. Linear driver designs (even if they have PWM for brightness) are MUCH simpler. I (or anyone with a basic understand of electronics) could design a driver with multiple brightness levels using a linear regulator in about 3 minutes and be 99.9999% confident that it will work perfectly the first time. Problem is, it won't be very efficient at all - and it will generate far more heat. Heat is the reason I did not go with a linear regulator.
Switched Mode supplies, though, are as much art as they are science. Especially in this case, the switch operates at very high speed, and signals stop looking like the nice pretty square waves that you would get in a perfect world. Our world isn't perfect, and all kinds of factors start to come in to play. Things like gate-charge-capacitance, trace length, cross-talk, EMI/noise.. Even the exact layout of the high current portion which includes the load (LED's), output capacitor, diode and switch (fet) - it matters.. The shorter that path can be kept, the better it will work.
It is pretty amazing it all works, actually :) So many factors work against a design being functional - and the only thing working for it is the designer who's trying to take hundreds of different variables into account and make them all dance in harmony. Every single part has it's strengths and weaknesses - overestimate one strength or underestimate one weakness (such as I did with the gate-charge) and you have a door-stop rather than a functional design. Sometimes, it's just the way you ran one trace next to another on the circuit board that renders a design worthless - route a high-impedence analog signal next to a high speed and high current carrying one, and you end up with so much cross talk that the intended signal is completely washed out.
I hope that you, and others following this thread, are learning a lot, and maybe gaining some appreciation (as you said) for just how much goes into making something like this work. It's a fun ride to take - and even when things don't work out (like they didn't in my first try), you get to learn something.
The new circuit boards are going to be a few more days delayed. Since I have much more confidence in Rev B, as I've tested everything and only made one change (which has been partially tested by wire-wrapping it in), I'm pretty sure everything is going to work. Based on that confidence, I've asked the circuit board shop to make the board with pads finished in Gold rather than HASL (Hot-Air Solder Leveling). Gold finish will give me a much flatter surface - not really a big deal on the side where the parts go, but it will allow a much better thermal bond on the back side where the copper mates with the aluminum enclosure. The gold doesn't really add much to the cost (about 10 bucks, in fact), but it does take the circuit board shop an additional two business days to process the boards. The little bit of extra time is worth it to me.
Earlier this evening, I soldered the blue-tooth module down. I'm tired, and I'm not going to do anything more with it tonight, but tomorrow or tuesday, i'll start trying to make a connection to it. We'll see how the signal does through the enclosure.
PPtk