5.4 Computer-Aided Drawing (CAD) & Engineering Graphics

PRC Electronics Engineering Licensure Examination Study Guide Exam

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1 Chapter 1: Introduction & Board Exam Strategy

1.1 PRC ECE Licensure Exam Overview & Regulation 1.2 Table of Specifications & Exam Strategy

2 Chapter 2: Mathematics Foundations

2.1 College & Advanced Algebra 2.2 Trigonometry & Solid Mensuration 2.3 Analytic Geometry & Differential Calculus 2.4 Integral Calculus & Applications

3 Chapter 3: Advanced Mathematics for ECE

3.1 Differential Equations & Circuit Transients 3.2 Complex Numbers & Laplace Transforms 3.3 Fourier Series, Fourier Transforms & Z-Transforms 3.4 Vector Analysis, Matrices & Probability

4 Chapter 4: GEAS - Engineering Sciences & Economics

4.1 Engineering Physics & Materials Chemistry 4.2 Engineering Mechanics & Strength of Materials 4.3 Engineering Economics & Financial Analysis 4.4 Computer Fundamentals & C/C++ Programming

5 Chapter 5: GEAS - Management, Materials, Environment & CAD

5.1 Engineering Management & Technopreneurship 101 5.2 Materials Science & Engineering 5.3 Environment Science & Engineering 5.4 Computer-Aided Drawing (CAD) & Engineering Graphics

6 Chapter 6: GEAS - ECE Laws, Ethics & Contracts

6.1 Republic Act No. 9292 (Electronics Engineering Law of 2004) 6.2 ECE Code of Ethics & Professional Conduct 6.3 Contracts, Specifications & National Building Code (PD 1096)

7 Chapter 7: Electronics Engineering - Circuits & Semiconductor Diodes

7.1 DC & AC Circuit Analysis & Network Theorems 7.2 Electromagnetics & Passive Components 7.3 Semiconductor Physics & Diode Circuits 7.4 Power Supply Design & Voltage Regulators

8 Chapter 8: Electronics Engineering - Transistors & Analog Circuits

8.1 BJT Operation, Biasing & Small-Signal Amplifiers 8.2 FET Characteristics, Biasing & Amplifier Circuits 8.3 Multistage Amplifiers, Frequency Response & Power Amplifiers 8.4 Operational Amplifiers & Active Filter Design

9 Chapter 9: Electronics Engineering - Digital Electronics & Control Systems

9.1 Feedback Topologies & Oscillator Circuits 9.2 Boolean Algebra, Logic Gates & Combinational Circuits 9.3 Sequential Logic, Flip-Flops & Microprocessor Architecture 9.4 Industrial Power Electronics & Control System Theory

10 Chapter 10: EST - Communications Fundamentals & Transmission Lines

10.1 Signal Fundamentals, Decibel Calculations & Noise Analysis 10.2 Amplitude Modulation (AM) Principles & Receivers 10.3 Frequency Modulation (FM), Phase Modulation & Discriminators 10.4 Transmission Line Parameters, SWR & Smith Chart

11 Chapter 11: EST - Digital Communications, Wireless & Optical Systems

11.1 Pulse & Digital Modulation Systems 11.2 Data Communications, OSI Model & Protocols 11.3 Antenna Principles & Electromagnetic Wave Propagation 11.4 Optical Fiber, Microwave, Satellite & Philippine NTC Regulations

5.4 Computer-Aided Drawing (CAD) & Engineering Graphics

Key Takeaways Explain This Topic AI

Orthographic projection represents a 3-D object with the standard multiview set: front, top, and right side views.

The Philippines commonly uses third-angle projection; the convention is signaled by a projection symbol in the drawing's title block.

CAD object snaps (ENDpoint, MIDpoint, CENter, INTersection, PERpendicular, TANgent) force precise cursor placement and prevent gaps or overlaps in fabrication-ready drawings.

Electronic schematic symbols follow IEEE 315 / IEC 60617, while PCB layout rules follow IPC-2221 and IPC-A-600.

Last updated: July 2026

5.4 Computer-Aided Drawing (CAD) & Engineering Graphics

GEAS lists Computer-Aided Drawing (CAD) as a practical skill area. For ECEs, CAD means producing and reading the schematic diagrams, PCB layouts, and mechanical drawings that communicate a design to fabricators and regulators.

1. Engineering Drawing Fundamentals

Engineering drawings use standardized projections and conventions:

Orthographic projection : representing a 3-D object in 2-D by projecting views onto mutually perpendicular planes. The standard multiview set is front, top, and right side .

Isometric projection : a single pictorial view with the three principal axes 120 degrees apart, preserving scale along each axis.

First-angle vs third-angle projection : first-angle places the view on the far side of the object (common in Europe/ISO); third-angle places it on the near side (common in the US and the Philippines). The choice is signaled by a projection symbol in the title block.

Scale : ratio of drawn size to actual size (1:1 full, 1:2 half, 2:1 double).

Line conventions : visible (continuous thick), hidden (dashed), center (chain dashed), dimension/extension (continuous thin), phantom (long-dash double-dash) for alternate positions.

2. Dimensioning & Tolerancing

Dimension lines show measurements; extension lines offset from the object; leaders point to features.

Tolerances specify allowed variation, e.g., 25.00 ± 0.05 mm 25.00 \pm 0.05\text{ mm} 25.00 ± 0.05 mm .

Limits : the maximum and minimum acceptable sizes.

Fits : clearance, transition, and interference fits between mating parts; the ISO hole/shaft-basis system standardizes fit classes (e.g., H7/g6).

Worked Example: Tolerance Stack on a Bearing Fit

A shaft is dimensioned 20.00 ± 0.02 mm 20.00 \pm 0.02\text{ mm} 20.00 ± 0.02 mm (max 20.02 20.02 20.02 , min 19.98 19.98 19.98 ) and its bearing bore 20.10 ± 0.03 mm 20.10 \pm 0.03\text{ mm} 20.10 ± 0.03 mm (max 20.13 20.13 20.13 , min 20.07 20.07 20.07 ). The nominal clearance is 20.10 − 20.00 = 0.10 mm 20.10 - 20.00 = 0.10\text{ mm} 20.10 − 20.00 = 0.10 mm . The minimum clearance occurs with the largest shaft and smallest bore: 20.07 − 20.02 = 0.05 mm 20.07 - 20.02 = 0.05\text{ mm} 20.07 − 20.02 = 0.05 mm . The maximum clearance occurs with the smallest shaft and largest bore: 20.13 − 19.98 = 0.15 mm 20.13 - 19.98 = 0.15\text{ mm} 20.13 − 19.98 = 0.15 mm . The clearance therefore ranges from 0.05 mm 0.05\text{ mm} 0.05 mm to 0.15 mm 0.15\text{ mm} 0.15 mm .

3. CAD Software Environment

Typical 2-D/3-D CAD packages (AutoCAD, SolidWorks, KiCad for ECE schematics and PCBs, Altium) share a common environment:

• Element Purpose
• Drawing area / canvas The graphical workspace
• Command line / ribbon Issues commands; many users type shortcuts
• Layers Organize object types (dimensions, hidden lines, wiring, copper)
• Snaps & grid Precision placement; snap to endpoints, midpoints, centers, intersections
• Construction elements Lines, circles, arcs, splines, polygons
• Blocks / symbols Reusable entities (resistor, capacitor, IC footprint)
• Dimensioning tools Auto-generate aligned, linear, angular, and radius dimensions
• Plotting / printing Output to scale on paper or PDF
• Snapping Precision

Object snaps (OSNAP) force the cursor to geometrically significant points: ENDpoint, MIDpoint, CENter, INTersection, PERpendicular, TANgent, QUAdrant, NODe . Snapping is essential to producing closed, dimensionally accurate drawings; freehand "eyeball" placement creates gaps and overlaps that fail fabrication.

4. ECE-Specific Drawing Standards

Electronics drawings follow specialized standards distinct from mechanical drafting:

Schematic diagrams (ANSI/IEEE 315 and IEC 60617 symbols): show logical electrical connections; component values and reference designators (R1, C2, U3) are labeled.

PCB layout (IPC-2221, IPC-A-600): copper traces, pads, vias, silkscreen, and solder mask, controlled by design rules (trace width, clearance, annular ring).

Wiring/connection diagrams : physical wiring harnesses.

Block diagrams : functional system decomposition (used in ECE system design and RA 9292 scope documentation).

Philippine Electrical Code (PEC) drawings: lighting/power layouts and single-line diagrams, relevant where ECE work interfaces with electrical installation.

Title Block & Sheet Sizes

Every engineering drawing carries a title block in the lower-right corner identifying the drawing number, title, scale, projection symbol, general tolerances, material, the drawn-by / checked-by / approved-by names, the date, and the revision history. Standard sheet sizes follow the ISO A-series (A0 through A4) or ANSI sizes (A through E); the Philippines commonly uses ISO A-sizes for technical drawings.

First-Angle vs Third-Angle Projection, Made Concrete

The distinction is purely where the right-side (or top) view is placed relative to the front view, but it is the single most common source of reading errors on a drawing. In third-angle (US/Philippine) practice, the top view is placed above the front view and the right-side view to the right of the front view — that is, each view is placed on the side of the object nearest the viewer, as if you unfolded the glass box around the object toward yourself. In first-angle (European/ISO) practice, the views are mirrored in placement: the top view appears below the front view and the right-side view to the left , because each view is projected onto the plane on the far side of the object and then unfolded. The trapezoidal projection symbol in the title block (a truncated cone drawn in both conventions) is the authoritative signal; always confirm it before interpreting an unfamiliar drawing. Getting this backwards flips the meaning of holes, pockets, and tapers, which is a classic fabrication error.

Dimensioning Rules and Why Tolerancing Matters

Good dimensioning follows a few rules that GEAS tests implicitly: dimension to visible (not hidden) outlines wherever possible; place dimensions outside the object outline; do not duplicate a dimension already implied by another view; stagger parallel dimension lines for legibility; and dimension from a common datum or baseline for accuracy. Tolerancing exists because no manufactured feature lands exactly on its nominal value; the tolerance band sets the functional limit. A clearance fit (hole larger than shaft) allows relative motion, a transition fit is borderline, and an interference fit (shaft larger than hole) requires pressing the parts together and holds by friction or elastic grip. The worked bearing example earlier showed how shaft and hole tolerances combine through worst-case stacking to give a clearance range. In PCB work the analogous idea is the design rule : minimum trace width, minimum clearance to adjacent copper, and minimum annular ring around a via must all be met by the fabricator's capability, or the board will not manufacture reliably.

Putting CAD Into ECE Practice

For an ECE, the CAD workflow typically moves from schematic capture (logical connectivity, reference designators, part values) to netlist extraction to PCB layout (placing footprints, routing copper under design-rule constraints, generating Gerber and drill files). Modern EDA tools (KiCad, Altium Designer, Cadence OrCAD) embed electrical rules — unrouted nets, unconnected pins, clearance violations — that mechanical CAD does not, so the drawing discipline is coupled to circuit correctness. A clean schematic that follows IEEE 315/IEC 60617 symbols and consistent reference designators is readable by any other engineer and is the legal record of the design; RA 9292 places professional responsibility on the signing ECE for plans and specifications, so drawing standards are an ethics issue, not just a craft one.

5. Summary

• Drawing concept Standard / rule
• Multiview set Front, top, right side
• PH projection convention Often third-angle
• Object snaps END, MID, CEN, INT, PER, TAN
• Schematic symbols IEEE 315 / IEC 60617
• PCB design rules IPC-2221 / IPC-A-600
• PH EIA system PD 1586 (covered in 5.3)