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Schematic Diagrams

Because different electronic components have different characteristics, it is necessary to distinguish between them in any circuit diagram. Of course, we could use the block diagram approach, and just identify each component with words. Unfortunately, this takes up a lot of space and makes the overall diagram harder to recognize or understand quickly. We need a way to understand electrical diagrams far more quickly and easily.

The answer is to use schematic symbols to represent electronic components, as shown in the diagram to the right. In this diagram, we show the schematic symbol of a battery as the electrical source, and the symbol of a resistor as the load. Even without the words and arrows, the symbols define exactly what this circuit is and how it behaves.

The symbol for each electronic component is suggestive of the behavior of that component. Thus, the battery symbol above consists of multiple individual cells connected in series. By convention, the longer line represents the positive terminal of each cell. The battery voltage would normally be specified next to the symbol.

The zig-zag line represents any resistor. In most cases, its resistance is specified next to the symbol just as the battery voltage would be given. It is easier and faster to read the symbol and the legend "4.7k" next to it, than to see a box and have to read "4700-ohm resistor" inside it.

As we introduce various electronic components in these pages, we will provide their schematic symbols as well.

One of the problems that can occur with schematic diagrams is too many lines all over the page. It's not a big deal when there are only two components in the circuit, but think of what the complete diagram for a modern television receiver or even a radio receiver would look like. We need a way to reduce the number of lines showing electrical connections.

We can help reduce the problem by noting that one connection is common to all circuitry, and serves as the reference point from which all electrical measurements are made. This electrical connection is designated the "ground reference," or simply "ground," in the circuit. The modified schematic diagram is shown to the right.

This circuit is actually the same as the one above, with the voltage source designated "E" (for EMF or ElectroMotive Force) and the load designated "R" (for Resistance). The ground symbols ( ) are assumed to be electrically connected to each other without any explicit connection shown. Often a circuit will be constructed on a steel or aluminum chassis, in which case the chassis itself is commonly used as the electrical ground as well as the mechanical support for the circuitry.

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