Designing Embedded Hardware

Chapter 3. Power Sources

The attention span of a computer is only as long as its electrical cord.

—Turnaucka’s Law

There is one important aspect that must be included in all embedded computer designs—power. In this chapter, we look at power sources for your computer and voltage regulation to keep your power smooth and reliable.

Your embedded computer system needs electricity. You have several options when it comes to powering your system: coal, nuclear, hydro, geothermal, or batteries. The first four fall under the general category of “juice from the wall.”

Juice from the Wall

If your system doesn’t need to be portable, this is the most obvious choice. What comes down the pipe is AC and far too high a voltage to be of immediate use to a digital system. It must be converted to a DC voltage of significantly lower magnitude. There are plenty of solutions for doing this. You can use DC lab power supplies, standard PC supplies (probably overkill for your needs), or AC adapters. The last of these is probably the best choice for most applications.

AC adapters (also known as plug packs or sometimes power bricks) are the little black boxes that come with your cell phone and a host of other appliances. They are a cheap, easy, and reliable solution and can be purchased from any good electronics vendor. Typically, they will provide an output voltage somewhere in the range of +5VDC to +12VDC and can supply a current of up to 500mA, depending on the particular plug pack. Choose one that can supply ...