Practical Electronics: Components and Techniques

Appendix B. Schematics

Schematics are the lingua franca of electronics. Someone trained in electronics in China can look at a schematic created in Sweden and immediately understand what is being described by the symbols in the diagram. In its most basic form, a schematic shows the connections between the various components in an electrical or electronic device. More abstract forms can be used to describe functional relationships between components or subsystems or define an equivalent circuit.

The symbols used in electronic schematics have evolved over the years from early pictorial representations to the standardized symbols in use today. By the 1920s, most of the symbology used today was in regular use, with regional variations for some of the components. For example, even today, schematics created in places other than the US might use rectangles for resistors, along with other minor differences. The standard “IEC 60617 - Graphical Symbols for Diagrams” from the International Electrotechnical Commission (IEC) defines over 1,900 symbols, but obtaining a copy of the standard is rather pricey. This appendix describes a subset of the standard symbols in common use in the eletronics field.

An electronic schematic does not say anything about the physical arrangement of the components in a circuit. When you are reading a schematic and comparing it to an actual piece of hardware, it is not uncommon to find, say, R22 and R23 near each other on the schematic, but on opposite sides of ...