An electrochemical cell (such as a common dime-store battery) is shown by two parallel lines, one
longer than the other. The longer line represents the plus terminal. A true battery, which is a com-
bination of two or more cells in series, is indicated by several parallel lines, alternately long and
short. It’s not necessary to use more than four lines to represent a battery, although you’ll often see
6, 8, 10, or even 12 lines. Symbols for a cell and a battery are shown in Fig. 4-2.
56 Direct-Current Circuit Basics
4-2 Schematic symbols for
an electrochemical
cell (A) and an
electrochemical battery
(B).
4-3 Meter symbols can have
the designator either
outside the circle (A) or
inside (B). In this case,
both symbols represent
a milliammeter (mA).
Meters are portrayed as circles. Sometimes the circle has an arrow inside it, and the meter type,
such as mA (milliammeter) or V (voltmeter) is written alongside the circle, as shown in Fig. 4-3A.
Sometimes the meter type is indicated inside the circle, and there is no arrow (Fig. 4-3B). It doesn’t
matter which way you draw them, as long as you’re consistent throughout a schematic diagram.
Some other common symbols include the incandescent lamp, the capacitor, the air-core coil, the
iron-core coil, the chassis ground, the earth ground, the ac source, the set of terminals, and the black box
(general component or device), a rectangle with the designator written inside. These are shown in
Fig. 4-4.
Schematic and Wiring Diagrams
Look back through the earlier chapters of this book and observe the electrical diagrams. These are
all simple examples of how professionals would draw schematic diagrams. In a schematic diagram,
the interconnection of the components is shown, but the actual values of the components are not
necessarily indicated. You might see a diagram of a two-transistor audio amplifier, for example, with
resistors and capacitors and coils and transistors, but without any data concerning the values or rat-
ings of the components. This is a schematic diagram, but not a true wiring diagram. It gives the
scheme for the circuit, but you can’t wire the circuit and make it work, because there isn’t enough
information.