I built an Atmega 328 on stripboard to control 3 small servos (which will never have a heavy load) and I had assumed that a 7805 voltage regulator would be sufficient for both the Atmega 328 and the servos.
It worked fine with my servos but when the friend I made it for tried his servo it would not work. I eventually discovered that his digital servo was drawing more power (probably just for an instant at startup) so I added a second 7805 so that the servos can't interfere with the Atmega 328. Now it works fine with 3 digital servos all working at the same time.
...R