The electronics for the speaker system can be split into two main sections—the power circuit and the audio circuit.

The circuit structure of the electronics is shown in the following diagram:

The speaker system block diagram

Note the color coding of the wiring. Here, black shows the power ground, gray shows the audio ground, cyan shows the unamplified audio, blue shows the amplified audio, yellow represents the battery voltage, and red shows 5 V.

Note the color coding of the wiring. This is important as it is the most common way in which different signals and power supplies are identified within an electronic product. There are a few common conventions that, while are not used here, are good to know; black is always ground, red and yellow usually indicate a power supply (5 V and 12 V, respectively), and yellow and green stripes usually represent a mains earth.

For small projects, such as this, following a standard color code for wiring is not as important. Different signals...