Eventually I will be running my project with an ATmega168. My project will require splitting the external power say from 12V into two separate circuits connected to the same ground. If I were to feed 12V into 2 7805 regulator chips with 100uF capacitor on each side of both 7805s, would that work? Or would I need slightly lower capacitors?
The data sheet suggests 0.33 uF on the 7805 input and 0.1 uF on the output, but some people use 1 to 10 uF on both.
What is used on the input depends on the power supply. If it is just full wave rectified AC, obviously you need a much larger capacitor on the input.