Just For Starters
certain industries) for what symbol
represents each type of ground, so
you usually must determine that from
10 Ω 25 W
Figure 4. Resistors.
Perhaps the most common
electrical component is the resistor,
which is found in practically every
circuit. Resistors are so simple and
ubiquitous that they are almost
always represented as a series of zigzag lines. Figure 4 illustrates resistors
accompanied by various attributes,
such as resistance (in Ω), tolerance,
and power rating. Schematic
diagrams do not usually specify every
possible attribute of each resistor. An
organization may have a default set of
attributes for all resistors (e.g., 5%
tolerance, 0.1 W, 0603 package).
Therefore, only each resistor’s value
(e.g., 10 Ω) must be included in the
diagram. Exceptions to the default
attributes, such as a resistor with a
higher power rating, can be noted in
the schematic diagram as text next to
the appropriate resistors.
Each unique component in a
schematic diagram typically contains a
unique reference designator, which is
simply a unique identifying label.
Resistors take the form “Rx,” where “x”
increments from one up to whatever
number of resistors are in the design.
Figure 3. Ground Nodes.
capacitor attributes are explicitly
mentioned as necessary.
(normally closed) configurations.
How a switch or button is drawn
depends on the operation of the
physical component. As such, you
will encounter new variations from
time to time.
Many projects include switches
or push buttons to control the
circuit’s behavior. Like many other
symbols, switches and buttons are
drawn to represent what they actually
do: make and break electrical contact
between two or more terminals.
Figure 6 shows several styles of
switches and push buttons that
use “SWx” as the reference
designator format. Common
switch configurations include
single-pole-single-throw) and DPDT (
can be drawn in either N.O.
(normally open) or N.C.
Discrete semiconductor components, such as diodes and transistors,
are found in many circuits. There are
several basic types of diodes and
transistors, but there are many
specialized variants, each with its own
symbol. Figure 7 shows the basic
Figure 5. Capacitors.
0.22 uF 10%
The capacitor is another ubiquitous
component in most circuits.
Capacitor representations generally
reflect the basic structure of a capacitor:
two metallic “plates” separated by an
insulating dielectric. Capacitance is
measured in Farads and capacitors
also have voltage ratings, which are
sometimes specified in the schematic
diagram. Figure 5 shows various
capacitor symbols, each of which
has a “Cx” reference designator.
Capacitors may be polarized or non-polarized. A polarized capacitor is
indicated by either placing a “+” near
the positive lead, curving the negative
plate, or both. As with resistors,
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