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Let there be light: Light emitting diodes ...........................................

A diodesends out light when you pass an electric current through it. LEDs,

which we use quite a bit in the projects in this book, are similar to the tiny,

twinkly lights you use to decorate a Christmas tree, and they come in a vari-

ety of colors, such as red, orange, yellow, green, blue, and white. Blue and

white LEDs are a lot more expensive, so you don’t see them used that often in

this book. (We’re thrifty!)

LED color isn’t controlled by the plastic that surrounds the light. Rather, the

semiconductor material used in the LED determines the color. The plastic

surrounding the semiconductor material can be clear or treated so that it dif-

fuses the light.

In addition, you can get LEDs in several sizes and shapes. The standard LED,

which is a cylinder with a diameter of 5mm, is referred to as T-1^3 ⁄4.

If you don’t connect LEDs the right way, you could wait forever to see the

light. Connect the longer of the two leads to the positive voltage and the

shorter of the two leads to ground or the more negative voltage.

Speaking up about speakers ...............................................................

Everybody knows what a speaker is: There’s one on your DVD player, your

computer, your iPod — you name it! Most speakers contain a permanent

magnet, an electromagnet, and a cone-shaped device from which the sounds

emerge (see Figure 3-9).

Permanent magnet

Electromagnet

Cone

Figure 3-9:

The parts

that make

up a

speaker.

50 Part I: Project Prep