Quote Originally Posted by xnihilo View Post
What's wrong if both supplies are connected at the same time in parallel???
what happen if you connect a 5 volt directly to a 3v battery?

Filtering capacitors? What do they filter?
voltage regulator output, battery... yeah you may think battery don't produce noise.. well yes and no, they have internal resistor, everything that need juice will make the voltage drop a little bit, knowing there's a clock source somewhere and you will also drive something, the voltage will swing accordingly.

Do a test, remove all capacitors, do a led blink (10mSec or so) then use your scope to monitor your Vdd rails... cool huh? now add the mandatory filtering caps... how better now?

Voltage drop? Right... 2.4v is a little too low, knowing the PIC will be fine down to 2V but I can't use 8MHz anymore if using 2V... In this case I can use 3*1.5v batteries instead and use 1N4001 diodes, right?
Sounds right

I disabled Brown Oout Detect in the config words, do I still need to care about this feature?
No, it will be disabled. It's not a bad idea to have it enabled so far. Just look the datasheet to know it's threshold and what advantage it may give you.

What fancy system are you talkning about?
Don't worry, way to complicated....