So why, when you can buy an AM radio for $7.95, would you decide to build one yourself with parts that cost $30? That’s a good question. The truth is just about everything you build in the projects included in this book — and most of the circuits floating around on the Internet — is something that you could probably buy in some form somewhere. But where would the challenge be in that?

Here’s why hundreds of thousands of electronics junkies build instead of   buying: Because they can. They can make something that grabs music out of the airwaves or sets off a light display or sends a little cart wheeling around the room themselves. We guess this is why people knit sweaters instead of buying them or work on old cars instead of taking them to mechanics. It just feels good to master something on your own.

Sounding off, Let there be light and good vibrations of this electronics session are where you can find all these cool projects, divided into categories by what the projects do, such as producing light, sound, or motion. Some of the things that you build in this book are just for fun, like the dancing dolphin light display (let there be light section). Other things have a practical use: the Couch Pet-ato (Good vibrations section) keeps your cat off the furniture when you leave the house, for example. Besides building gadgets that have a use, in some cases, you can build items more cheaply than you can buy them in the store. You could just end up with projects you can put to work and save a few bucks in the process.