arusr:
Wow, thanks for the tip. Can I ask what the components in red are? Are you taking about the built-in (less efficient) regulator, and powering the Arduino Mini directly from 3xAA battery at about 4.5V? Does that work? Is it still running at 16MHz? I'm wondering what the other parts are. If you wouldn't mine describing it, I'd appreciate it.
Yep. It's the voltage regulator, the power LED, some diodes+capacitors. Basically the power supply. Whoever designed that board grouped them all together nicely. You might be able to remove less of them, I just removed parts until it did what I wanted (I could see where the crystal was so I didn't touch that...)
3xAA won't actually give 4.5V for most of the lifetime... but what it gives should be fine for running this.
arusr:
I think if I want to run a 8MHz, I'd need to build my own Arduino right? I can't make the Arduino Mini Pro run at 8MHz because it's already got a built in 16MHz oscillator?
The Mega328 has an internal 8MHz oscillator. It will run at 8MHz. if you set the "fuse bits" to select it. It will use less power and run at lower voltages if you run at 8MHz.
But ... if you're going to do that you might as well use a bare Mega328 chip - you're not using any of the components of the Pro Mini. Mega328 s can run at 8MHz with no external components. The only reason I hack Pro Minis is because I want the 16MHz crystal.
With correct fuse settings you can even make it run at 1MHz (and it will work with 2xAA!)