The Arduino BT uses a dc to dc converter (max1676) instead of a 7805 type voltage regulator used on most other Arduino boards
Since the max1676 steps up voltage, that makes it clear how the board can be powered with voltages well below 5V. Its not that I actually NEED to use a 9V battery, but really want to understand the limits of the stock board, and just how to power it correctly. Here's what I now think I understand: Looking at the photo I posted, I can power the board by putting a power supply that delivers between 1.2 and 5.5 Volts to the two post screw down terminal at the far lower left of the picture, with ground (-) to "2" and (+) to "1".
Where it says:
5V Gnd 9V
x x x x
Is this terminal block just intended to power other components? I.e. the board should always get its input power from the posts marked "1" and "2" at the far lower left of the board? I'll probably burn things out if I actually connect 9V (+) to where it says "9V" [and (-) ground to one of the two "Gnd" terminals]. In fact, where it says "9V" that really just deliver the raw (+) input voltage that I input at terminal 1 at the far lower left of the board. At this same terminal block though, I can use the 5V to power other components that require 5V, since it will deliver the stepped up voltage from the max1676. Is it fair to say I should just steer clear of the terminal with the 9V designation, and treat that label as an error? This 9V terminal only applies on a non BT board, where (+) 9V was delivered to the far left terminal "1"?
Again, I hate to seem dense--truly, just trying to learn a bit here...