Creating a simple but stable 5v supply
The question came up on the Chibots mailing list about creating a stable 5v supply for the electronic components of a robot. It is true that motors, servos and even sensors can wreak havoc on your regulated supply. Electrical noise is a complex issue, there are a huge number of books on the subject and googling it will return more hits that you'll care to count. I will share with you what has worked for me and we'll use our current Robomagellan bot as an example.
The regulator is connected to the battery through a 1A diode. There are several types of diodes you can use with varying voltage drops but since the supply is 12v and we want 5v, the voltage drop of the 1N4001 isn't critical. The purpose of the diode is to help protect the regulator from voltage drops that can be caused by the motors when they draw large amounts of current. C1 acts as a tiny battery, filling in when the voltage drops small amounts, helping to keep the voltage supply above the critical mark for the LM7805. The capacitors along with the diode keep the input voltage high enough that the 7805 can maintain a steady 5v.
There are numerous ways that you can improve this circuit. To increase efficiency, you can use a switching regulator instead of a linear regulator. You can use a series of diodes and capacitors to increase the voltage drop protection. I have seen coils in line to help smooth out voltage ripples.
Sparkfun has an article on creating a 5v supply that is very similar to my approach - Sparkfun Tutorial on Power Supplies
I encourage others to share your power supply circuits that have worked in noisy environments. Share the wealth!