Electronics: Diagrams and Schematics

• Electronics involves controlling electrons in devices using low voltage, amperage, and signal paths.
• In the electronics industry, technicians are also known as electronic drafters.
• Technicians convert engineering sketches or instructions into formal drawings or revise existing ones.
• Drawings made by technicians should be neat, organized, and use proper symbols.
• Technicians should have a strong understanding of electronic technology.
• Knowledge of product function is important for advancement in the electronics industry.

Electronic Diagrams

• Electronic drafting utilizes similar diagrams to electrical drafting.
• The difference between the two is minor in appearance.
• Electrical power transmission systems and intricate electronic systems necessitate separation between electrical and electronics discipline.

Block Diagrams

• Block diagrams outline the path of a signal through steps or operations.
• Block diagrams provide a quick overview of the relationship between components in electronic equipment.
• Blocks represent steps or operations, summarizing a schematic drawing.
• Square or rectangular blocks are the basic symbol in block diagrams.
• The largest title inside the block determines the size of the block, such as CONVERTER or AMPLIFIER.
• Block diagrams typically start in the upper-left corner, components are arranged from left to right.
• Graphic symbols are also often used to demonstrate Input Output of block diagrams (speakers, mics, antennas).
• Designers create block diagrams directly from a given schematic diagram.
• Block diagrams can also be prepared from pictorial diagrams.
• Dashed lines represent separate or optional components.

Schematic Diagrams

• Schematic diagram preparation is a primary stage in product development.
• Schematic diagrams offer basic circuit connection details for electronic items.
• Device functionality is represented by the stages in which system components are drawn.
• Reference designations, supplier identification, and values are used to label individual components.
• Reference designations link the component directly to the schematic drawing, using letters to identify the component.
  • Capacitor = C
  • Inductor = L
  • Resistor = R
  • Diode = D
  • Transistor = Q
  • Transformer = T
  • Switch = S
  • Semiconductor = CR
  • Integrated circuit = U
• Schematics should be uncluttered, easy to read, and follow standards.

Symbol Standards for Schematics

• Standard symbols are essential knowledge for drafters.
• It is useful to have IEEE 315, Graphic Symbols for Electrical and Electronic Diagrams, or company standards available as references.
• A symbol library or a template designed to IEEE standards is an excellent aid when using CADD.

Symbol Sizes for Schematics

• Symbol sizes may differ slightly based on the company or CADD software.
• The uniformity of symbols within a drawing is important.

Other Schematic Tips

• Knowledge of current standards is essential when working from rough engineering sketches.
• Note any odd details - are they intentional or an engineer's mistake? (EX: Line under resistor symbol)

Best Practices for Schematic Diagrams

• There exist several electronic drafting methods that are more widely recognized, and the beginning drafter should be familiar with them.
• Common applications sometimes change due to the situation or differences between national and company standards.

Active devices

• An active device is an electronic component that contains voltage or current sources, such as a transistor and integrated circuit.
• Transistors are semiconductor devices that act as conductors of electricity with resistance to electron flow.
• They can be used to transfer or amplify an electronic signal.
• The placement of active devices is a key part of the schematic layout, and they are often established first when designing schematics.
• Inputs are usually on the left, and outputs are on the right, with signal flow from left to right.

Bias Circuitry

• Bias refers to the voltage applied to a circuit element to control the mode of operation (fixed, forward, or reversed).
• DC biasing is the basic circuitry that makes any electronic device function.
• Resistors, placed vertically, should be as close as possible to the active device without crowding the drawing.
• Transistors can be drawn in two ways based on bias direction, changing the arrow direction.

Coupling Circuitry

• After bias circuitry, layout the coupling circuitry (connections between components).
• Drafter's aim: Adequate space for information while keeping the schematic compact and readable.

Schematic Layout Sketching

• Guidelines for layout, sketch on graph paper for estimating space for labels and values.
• Work from an engineer's design sketch that provides layout characteristics.
• The screened area for line crossings in engineering sketches needs clarification (connection or no connection?).

Sketching - Connections

• Resistors as part of the universal bias pattern indicate a connection is intended.
• Connections and nonconnections have standard representations.

General Sketching Suggestions

• Make a layout sketch on graph paper, block out areas next to the symbols for component labeling.
• The basic difference between optional layout vs standard layout is that the components attached to the top side of the active devices have been folded down.
• The folded-down form results in a long, narrow schematic, used when height is fixed but length can vary (foldout pages).

Labeling for Schematics

• Two parts to the schematic layout: Symbols and labeling.
• The designating system uses a letter for the component type followed by a sequence number.
  • First resistor in the upper left: R1; next resistor to the right: R2, and so on.
  • Capacitors: C1, C2, C3, etc
  • Transistor = Q
  • Inductor = L
  • Diode = D
• Number sequence flows: Left to right on simple circuits.
• Complex schematics may have multiple levels flowing from left to right and top to bottom.

Units Used for Parts Values

• Electronic component values range from extremely small to extremely large.
• Avoid large numbers by moving the decimal point in groups of three and changing the numerical name.
  • EX: 2,200 ohm resistor becomes 2.2 kilohms (2.2 k).
• Omit the word ohms, as resistors are assumed to be rated in ohms.
• Inexact unit areas exist in the parts value system, like with 500,000 (0.5 M or 500 k; 500 k is preferred).
• 1200 can be left as is or reduced to 1.2 k.

Placement of Numbers

• The reference designator and value numbers are typically placed:
  • Above horizontal components
  • Right side of vertically drawn components
• Other arrangements can cause confusion when components aren't adequately spaced.