In the new edition of the Arduino Cookbook, Michael Margolis gives a great step-by-step explanation of how to read a schematic and build a breadboard prototype from it. The following excerpt is adapted from Appendix B of the Cookbook.
Using Schematic Diagrams
A schematic diagram, also called a circuit diagram, is the standard way of describing the components and connections in an electronic circuit. It uses iconic symbols to represent components, with lines representing the connections between the components.
A circuit diagram represents the connections of a circuit, but it is not a drawing of the actual physical layout. Although you may initially find that drawings and photos of the physical wiring can be easier to understand than a schematic, in a complicated circuit it can be difficult to clearly see where each wire gets connected.
Circuit diagrams are like maps. They have conventions that help you to orient yourself once you become familiar with their style and symbols. For example, inputs are usually to the left, outputs to the right; 0V or ground connections are usually shown at the bottom of simple circuits, the power at the top.
Here are some of the most common components, and the symbols used for them in circuit diagrams:
Here is a schematic diagram that illustrates the symbols used in a typical diagram:
Components such as the resistor and capacitor used here are not polarized—they can be connected either way around. Transistors, diodes, and integrated circuits are polarized, so it is important that you identify each lead and connect it according to the diagram.
This drawing shows how the wiring could look when connected using a breadboard:
The finished breadboard illustrations were produced using a tool called Fritzing that enables the drawing of electronic circuits.
Wiring a working breadboard from a circuit diagram is easy if you break the task into individual steps. The next illustration shows how each step of breadboard construction is related to the circuit diagram.
The finished circuit is from Recipe 1.6 in the Cookbook, which produces a sound that is controlled by a light dependent resistor.