4.1 Symbol libraries

This step is often optional and rarely done for an established PCB design environment. However, for a new environment, the libraries that come with the tools may not include everything needed.

A “symbol” in this context is a symbolic graphical construct that represents a particular device or circuit. A symbol often does not look anywhere close to the physical part, as that is not important for a symbol. What is important is the logical pins of a symbol. If the device represented has 8 pins, then the symbol must have 8 pins.

Furthermore, a symbol often have pins that are captioned to let people the functions of the pins.

For certain symbols, such as resistors and capacitors, they are usually drawn in a universally recognized way.

In summary, a symbol:

• represents the logical function of a device
• has the same number of pins as the physical device
• may have pin captions to indicate how pins should be used
• may have a standardized shape
• may have misc. optional graphical elements that describes the represented device