I'm building a prop, and I've got a problem.
What you see here is an older model, which used a 555 timer and a 4096 chip to power a 7 led display. The 9v battery, which barely fit inside with all the wires once the top was down, was able to power that for a good 15 hours.
I am now building a new model which has 84 leds in it that will draw around 500mA of power. A 9v ain't gonna cut it. So, I've been looking at the possiblity of powering the thing with 6 AAA batteries, which would provide enough juice to get 15 hours out of it.
Problem is, those take up a lot of space. And as you can see, I don't have a lot of space.
The box you see there is around 4.5x3x1.25". Just tall enough to fit a 3x2 configuration of AAA batteries, but probably too narrow to fit 6 side by side, unless I orient them along the length of the thing.
I think one of those configurations will be okay, because the Pro Mini is a lot smaller than my original circuit board, and the wiring this time around should be a bit neater since I will be using ribbon cable to bridge between 10 segment led displays, but I want to be prepared for the worst case scenario where I have to reduce the number of batteries I have in there.
I'm thinking I have one of two options here. Either I can find a way to power the 5v Pro Mini off 6v, or I have to buy a 3v basic breakout board and a 3v Pro Mini, and run it off of that instead. (You do need a 3v basic breakout board to program the 3v Pro Mini, correct?)
Thing is, I'm not sure what the best way to go about dropping the voltage would be. I've looked into switching regulators but those are pretty expensive. I've also considered the possibility of using a diode to drop the voltage to a little over 5v and connect my power source directly to Vcc, but I'm not sure if that would dramatically reduce the amount of time I can run it off the batteries. I may be no better off than using the 9v if I do that. On the other hand, I'm concerned about the 8mhz Pro Mini's ability to drive my array, though since I'll be switching between only 8 columns of LEDs at 60hz, it'll probably be fast enough. (Really didn't want to have to spend money on another breakout board though.)
Anyway, I'm interested to know what you think would be the best way to proceed here.