Back-Up Battery Detection

[HooctAwnFonix]

I'd like to give my Arduino a back-up battery. I've read about a slick way of doing this by hacking a USB-A cable and putting your back-up battery on it - by default, the Arduino is hooked up to rely on the external power supply if it's available and to pull from the USB if it is not, so if the external PS goes out, it will automatically fall back on the USB connection if it's available. Now that's exactly what I wanted but I'd also like to know IF that has occured.

Assuming there will be a noticeable change in supply voltage when that happens, is there an easy way I can get the Arduino to notice that it's switched over?

[thefatmoop]

couldn't you just measure the external voltage through a voltage divider and put that into a digital input? If power goes out, the voltage will go low and you know it's running on battery power.


need more information if this isn't sufficient.

http://en.wikipedia.org/wiki/Voltage_di ... ve_divider

[HooctAwnFonix]

I was stuck thinking about giving the Arduino V-out to a circuit and designing it such that it would switch over to some different measurable state when the voltage supply changed... This is much more straightforward!

It looks like it would be pretty easy to add a wire to that PS input terminal too - now if I get a 5V power supply I won't even need to bother about voltage dividing!