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C H A P T E R E I G H T E E N

ELECTRONIC

DIAGRAMS

2

Technical Drawing with Engineering Graphics, 14/e

Giesecke, Hill, Spencer, Dygdon, Novak, Lockhart, Goodman

© 2012, 2009, 2003, Pearson Higher Education,

Upper Saddle River, NJ 07458. • All Rights Reserved.

OBJECTIVES

1. Identify common component symbols on an electronic

schematic diagram.

2. Draw a schematic diagram using standardized symbols.

3. Draw connecting and crossover paths.

4. Identify interrupted and uninterrupted lines.

5. Designate terminals and numerical values of components.

3





UNDERSTANDING ELECTRONIC

DIAGRAMS

Schematic Diagram. (Courtesy of September 1997 QEX: Copyright ARRL.)

A wiring diagram for a second-floor

house plan looks quite different from a

logic diagram.

Portion of a Single-Line Diagram Showing the First Floor Lighting

Plan for a Public Library. (Courtesy of Associated Construction

Engineering.)

4





Symbols

Standard Symbols

CAD Symbol Libraries

The symbols approved by the American National Standards

Institute (ANSI) are published in Graphic Symbols for Electrical

and Electronic Diagrams, ANSI/IEEE 200-1975 (R1989). In

addition, modern printed circuitry techniques, which are used

extensively in electronic equipment, require specially prepared

diagrams or drawings. Much of the material in this chapter is

extracted or adapted from that standard.

You can create or purchase libraries of standard electronic

symbols for use in electronic diagrams. CAD symbol libraries

should follow approved standards just as manually created

drawings would. When you create CAD drawings showing

electronic symbols, consider the final size of the plotted drawing.

Make sure that symbols you create or add to drawings meet

minimum size standards as set out in ANSI 14.2M.

(Courtesy of September 1997 QEX: Copyright ARRL.)

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Types of Electronic

DiagramsFunctional block diagram A functional block diagram shows the functions of major

elements in a circuit, assembly, or system using a simplified form. It is used to simplify the

representation of complex equipment by using blocks or rectangles to depict stages, units, or

groups of components in a system.

Functional Block Diagram for a Digital Downconverter. (Courtesy of September

1997 QEX: Copyright ARRL.)

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Types of Electronic

Diagrams continued…Single-line diagram

A single-line diagram shows the

path of an electrical/ electronic

circuit in a general format using

single lines and symbols.

Single-Line Diagram. (Courtesy

of CH2MHILL.)

7





Types of Electronic

Diagrams continued…Schematic diagram or circuit diagram A schematic diagram or circuit diagram shows the

electrical connections and functions of a specific circuit arrangement. It does not depict the physical

shape, size, or arrangement of the elements. This type of drawing is used to communicate the design,

construction, and maintenance information for electronic equipment. It facilitates tracing the circuit to

convey its function.

Schematic Diagram of a FET (field-effect transistor) VOM (volt-ohmmilliammeter).

(Courtesy of American Radio Relay League.)

8





Types of Electronic DiagramsConnection or wiring diagram A connection or wiring diagram shows the connections of an

installation or its component devices or parts. It may cover internal or external connections, or both,

and contains the level of detail to show the connections involved. The connection diagram usually

shows general physical arrangement of the component devices or parts. This type of diagram is

used to represent the wiring between component devices in electrical or electronic equipment.

Portion of a Connection Diagram. (Courtesy of Golden Valley Electric Association.)

9





LINE CONVENTIONS

AND LETTERING

ANSI recommends a line of

medium thickness for general

use on electrical diagrams. A

thin line may be used for

brackets, leader lines, and so

on. To emphasize special

features such as main signal

paths, a thicker line may be

used to provide the desired

contrast. For recommended line

thickness and lettering, refer

to ANSI/ASME Y14.2M.

Line Conventions for Electronic Diagrams

10





STANDARD SYMBOLS

FOR ELECTRONIC DIAGRAMS

A Portion of the Standard Showing Graphic Symbols for

Electrical and Electronics Diagrams. (Courtesy of IEEE.)

Symbols Symbols should

conform to an internationally or

nationally approved standard,

such as ANSI/IEEE 315.

Size of symbols Symbols should

be drawn roughly 1.5 times the size

of those shown in the IEEE 315A

standard.

Switches and relays Switches and

relays should be shown in the

“normal” position—with no operating

force or applied energy.

11





GROUPING PARTSWhen parts or components are naturally grouped, as in separately obtained

subassemblies or assembled components such as relays, tuned circuit transformers,

hermetically sealed units, and printed circuit boards, indicate the group using a dashed

line to enclose them in a “box,”

Portion of a Maintenance-Type Schematic Diagram of FM Weather Monitor

Radio. (Copyright Motorola, Inc. 1980. All rights reserved.)

12





ARRANGEMENT OF

ELECTRICAL/ELECTRONIC

SYMBOLSSymbol ArrangementArrange the various parts and symbols to balance

blank areas and lines. Provide sufficient blank

spaces adjacent to symbols to allow for reference

designations and notes. Exceptionally large

spaces give an unbalanced effect but may be

necessary to provide for later circuit additions. Of

course, using CAD, it is easy to move and stretch

the existing drawing to add space.

Signal PathArrange schematic and single-line diagrams

so that the signal or transmission path from

input to output proceeds from left to right and

from top to bottom when possible.

Supplementary circuits, such as a power

supply or an oscillator circuit, are usually

drawn below the main circuit.

Electronic Symbol Templates.

(Courtesy of Chartpak, Inc.)

Templates, such as those

below, save time when

drawing symbols.

13





CAD for ELECTRONIC

DIAGRAMS CAD can help you to produce complicated schematic drawings efficiently. As a minimum,

CAD software provides standard symbol libraries that make it quick to place the symbols

into a drawing. On the more complex side, CAD packages may automatically route traces

and simulate the circuit function.

AutoCAD Software Provides a Convenient Tool Palette to Use for Inserting Symbols.

(Autodesk screen shots reprinted with the permission of Autodesk, Inc.)

Symbol Arrangement

Arrange the various parts and symbols

to balance blank areas and lines.

Provide sufficient blank spaces adjacent

to symbols to allow for reference

designations and notes. Exceptionally

large spaces give an unbalanced effect

but may be necessary to provide for

later circuit additions. Of course, using

CAD, it is easy to move and stretch the

existing drawing to add space.

14





CONNECTIONS

AND CROSSOVERS

At times it is impossible to avoid drawing a line representing a conductor wire across

another conductor wire, where the wires cross but do not connect. These crossovers

must clearly depict that the conductors do not make a connection.

Connecting lines (for conductors) are typically drawn horizontally or vertically,

minimizing bends and crossovers. Avoid using long interconnecting lines.

15





INTERRUPTED PATHSInterrupted paths may be used for either a single line or groups of lines to simplify a

diagram. Label these carefully with letters, numbers, abbreviations, or other identification so

that their destinations are unmistakable. Grouped lines are also bracketed as well as

labeled. When convenient, interrupted

grouped lines may be connected by

dashed lines

(Courtesy of IEEE.)

(Courtesy of IEEE.)

16





TERMINALSWhen actual physical markings appear on or near terminals of a component, they may be shown on the

electrical diagram. Otherwise, assign arbitrary reference numbers or letters to the terminals and add a

simple diagram that associates the numbers or letters with the actual arrangement of terminals on the

component.

(Courtesy of Motorola, Inc.)

(Courtesy of IEEE)

(Courtesy of IEEE)

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COLOR CODINGTerminals or leads are frequently identified by colors or symbols, which should

be indicated on the diagram. Below are showd how the colors of the insulated

wire leads are noted near each terminal. Colors are shown on the drawing

using the following codes:

Typical Color Coding. (Courtesy of Motorola, Inc.)

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DIVISION OF PARTSFor clarity, draw sections of multielement parts separately in a schematic

diagram. Indicate subdivisions with suffix letters.

(Courtesy of IEEE.)

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ELECTRON TUBE PIN

IDENTIFICATIONElectron tubes are generally not used in new designs but are still commonly seen in high-power amplifiers.

You may see their symbols in maintenance diagrams used while troubleshooting or modifying existing

equipment. Electron tube pins are conventionally numbered clockwise from the tube base key or other

point of reference, with the tube viewed from the bottom. In the recommended method of pin identification

on a diagram, the corresponding numbers are shown immediately outside the tube envelope, adjacent to

the connecting line

(Courtesy of IEEE.)

Reference Designation, Type Number, and Function for Electron

Tubes and Semiconductors..Terminal Identification for Electron Tube Pins.

20





NUMERICAL VALUESAlong with reference designations, numerical values for resistance, capacitance, and inductance should

be shown, preferably in the form using the fewest

numerals. To do this, you can combine the

multipliers shown below.

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FUNCTIONAL IDENTIFICATION

AND OTHER INFORMATION

Other information that may be shown on schematic diagrams,

if desired, includes the following:

1. DC resistance of transformer windings and coils

2. Critical input or output impedance values

3. Voltage or current wave shapes at selected points

4. Wiring requirements for critical ground points, shielding

pairing, and so on…

5. Power or voltage ratings of parts

6. Indication of operational controls or circuit functions

Where functional designations (TUNER,OUTPUT, etc.) are to be shown on a panel or

chassis surface, they should also be shown on the electrical diagram in an appropriate

place. Test points may be identified by the words TEST POINT on the drawing.

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INTEGRATED CIRCUITSAn integrated circuit is a semiconductor wafer or chip that has been processed to

produce a microminiature replacement for discrete components, such as transistors,

diodes, resistors, capacitors, and connecting wiring.

A Typical Dual In-Line Package Integrated Circuit Representation.

(Courtesy of Motorola, Inc.)

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PRINTED CIRCUITSIn the interests of miniaturization and mass production, printed circuit (PC) boards

are widely used in the electronics industry, replacing expensive and tedious hand-

wiring manufacturing methods

Printed Circuit Pattern. (Lamit, G. Louis; Lloyd, J. Sandra, Drafting

for Electronics, 3rd, © 1998. Printed and Electronically reproduced

by permission of Pearson Education, Inc., Upper Saddle River,

New Jersey.)

It is important to maintain

close tolerances in the

production of PC artwork,

so that the various

electronic components’

leads will fit properly in the

spaces provided for them

on the finished board.

CAD circuit design

software should be utilized

whenever possible to

provide optimum PC

board designs with

minimal effort.

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COMPUTER GRAPHICS

CAD greatly simplifies the

process of producing printed

circuit artwork. Sophisticated

programs let you reduce the

physical size of the board and

minimize the need for crossover

jumper wires.

CAD systems are capable of

providing full-size or scaled

artwork along with other data

required to set up automated

soldering and drilling

equipment required to produce

a finished printed circuit board.

(Courtesy of Cadence Design

Systems, Inc. OrCAD is a

registered trademark of Cadence

Design Systems, Inc.)

0135090520_ppt18

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