Chapter One

You are probably very familiar with various schematic symbols and diagrams. A schematic is merely a collection of electronic symbols connected together with virtual "wires." The main reason you need a schematic when fabricating a printed circuit board is to provide input (a netlist) to your layout and routing tool. A netlist is a file, usually ASCII text, which defines the connections between the components in your design. Other uses for a schematic when fabricating boards include documentation, archiving, and the automatic generation of a bill of materials (BOM).

If your design is simple, you may not need to generate a schematic and it is possible to skip this step and proceed directly to layout and routing of the circuit board. However, you may still need to generate a netlist to feed to the layout tool.

The Schematic Symbol

For most circuits, a photograph or realistic drawing showing actual components and their interconnections would be far too complex to be of value in replicating the circuit. A schematic symbol is a simplified representation of a real-world component. A schematic diagram shows such representations of real-world components and a simplified "map" of how they are connected together. It would be silly to tape resistors and capacitors to a piece of paper, so instead we use drawings that represent those parts.

Schematic symbols come in all sizes and shapes. They can be as simple as stick figures or as complicated as a work of art, but they all have a few common features. These features are summarized below:

1) Ea