AVR-Chat

> ... there will be a number of components that I can't shut off and I 
don't want to run into the situation where the battery is bled dry.

If you can't allow a depleted battery (like LiIon and LiPos) you _must_ 
remove the load.  There exist LDO regulators that provide integrated 
power distribution switches; look at some USB power solutions like a 
TPS2148.  That part does not offer /Fail but you can, presumably, read 
the battery voltage with a resistive divider to an ADC input and make 
your own decision about when to shut down.  You could also, of course, 
use full battery management ICs, like most LiIon packs use.

You can also turn everything off with a simple suicide switch, a  MOSFET 
in series with the battery that's latched on by a processor control 
signal; remove the latching signal and the machine will stop - and stay 
that way since the battery is now disconnected.  You'll need a way to 
re-latch the switch to get going again, perhaps a pushbutton Start 
switch; I've heard described a way to do that with a DC power jack that 
will restart the processor as soon as a charger is attached, by using 
the sleeve shunt (the third jack pin).


Tom