The Engineering Design Process

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The Engineering Design Process

• ELEC 4000 Senior Design
• V. P. Nelson R. M. Nelms

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Outline

• What is design?
• The basic design process
• Design requirements specifications
• Design alternatives
• Modeling and simulation
• Implementation
• Testing

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Definition of Design

• International Technology Education Association
• The systematic and creative application of
  scientific and mathematical principles to
  practical ends such as the design, manufacture,
  and operation of efficient and economical
  structures, machines, processes, and systems.
• Accreditation Board for Engineering
  Technology
• Students must be prepared for engineering
  practice through the curriculum culminating in a
  major design experience based on the knowledge
  and skills acquired in earlier course work and
  incorporating engineering standards and multiple
  realistic constraints

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Design Constraints

• Multiple constraints usually apply
• Constraints are often conflicting
• Tradeoffs are often needed to satisfy
  constraints
• Examples

• Physical
• Economic
• Environmental
• Social
• Time to market
• Political

• Ethical
• Health and safety
• Reliability
• Manufacturability
• Sustainability
• Adherence to standards

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General Problem Solving Steps
Engineering Design, Alan Wilcox Figure 1.3
Define the problem Cause of problem
What is need? Requirements? What are
constraints?
Analysis
Generate and select possible solutions
Synthesis
Evaluate solution Consequences? Is it
reasonable? How well does it solve problem?
Evaluation
Select best solution
Decision
Implement best solution Coordinate
Control
Action
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The Engineering Design Process
Practical Engineering Design Bystrom Eisenstein
Figure 1.1
Identify Problem
Form Team
Develop Specifications
Generate Design Alternatives
Model Simulate
Document
Implement Prototype
Test
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Levels of abstraction
Requirements
What the customer wants
System functions/characteristics
Specification
Architecture
System block diagram (HW SW)
Component design
Individual HW/SW blocks
System integration
Combine blocks to create a system
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Requirements

• Plain language description of what the user wants
  and expects to get.
• May be developed in several ways
• talking directly to customers
• talking to marketing representatives
• providing prototypes to users for comment.

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Functional vs. non-functional requirements

• Functional requirements
• output as a function of input.
• Non-functional requirements
• time required to compute output
• size, weight, etc.
• power consumption
• reliability
• etc.

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Example GPS moving map requirements

• Moving map obtains position from GPS, paints map
  from local database.

I-78
Scotch Road
lat 40 13 lon 32 19
From Computers as Components by Wayne Wolf
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GPS moving map needs

• Functionality For automotive use. Show major
  roads and landmarks.
• User interface At least 400 x 600 pixel screen.
  Three buttons max. Pop-up menu.
• Performance Map should scroll smoothly. No more
  than 1 sec power-up. Lock onto GPS within 15
  seconds.
• Cost 500 street price.
• Physical size/weight Should fit in dashboard.
• Power consumption Current draw comparable to CD
  player.

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GPS moving map requirements form
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Specification

• A more precise description of the system
• should not imply a particular architecture
• provides input to the architecture design
  process.
• May include functional and non-functional
  elements.
• May be executable or may be in mathematical form
  for proofs.
• Contract between customer architects

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Typical Project Specifications

• Some specifications are absolute others may be
  negotiable
• Functionality (inputs, outputs, operating modes)
• Performance (speed, resolution, latency)
• Cost (NRE cost parts x RE cost)
• Ease of use
• Reliability, durability, security, fault
  tolerance
• Physical (size, weight, temperature, radiation)
• Power (voltage levels, battery life)
• Conformance to applicable standards
• Compatibility with existing product(s)

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GPS specification

• Should include
• What is received from GPS
• map data
• user interface
• operations required to satisfy user requests
• background operations needed to keep the system
  running.

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Architecture design

• What major components go to satisfying the
  specification?
• Hardware components
• CPUs, peripherals, etc.
• Software components
• major programs and their operations.
• Must take into account functional and
  non-functional specifications.

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GPS moving map block diagram
display
GPS receiver
search engine
renderer
database
user interface
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GPS moving map hardware architecture
CPU
display
frame buffer
GPS receiver
memory
panel I/O
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GPS moving map software architecture
database search
renderer
pixels
position
timer
user interface
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Design Alternatives

• Consider different design approaches that meet
  the specifications
• Most involve trade-offs some specifications can
  be modified, others cannot
• Define performance metrics that must be met
• Follow top-down design process
• Partition design into well-defined modules
• Design and test modules independently
• Integrate the modules into a system and test the
  system
• Partition functions between hardware vs. software
  
• Selection of components, programming languages,
  etc.
• Develop vs. purchase (use of Intellectual
  Property)

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Concept to Paper Design
Engineering Design, Alan Wilcox Pg. 31
Block diagram of system concept (one solution)
Partition into functional modules
Define purpose and function of each module
Decide split between hardware and software
Do for each module
Detailed block diagram (or algorithm)
Check for similar designs in past
Rough sketch of circuit (or program)
Detailed circuit design (or program)
Integrate hardware and software into system
Completed paper design ready for evaluation
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Engineering heuristics
Engineering Design, Alan Wilcox Pg. 36

• Dont reinvent the wheel read data sheets and
  application notes
• Reduce your problem to something youve solved
  before
• If you cant meet the specs, negotiate dont
  hide the problem
• Always have an answer you have to start
  somewhere
• Change one variable at a time when you adjust
  your design
• Develop circuits/programs module by module debug
  as you go
• Build a quick simple circuit for experimentation
  understand it
• Keep designs simple
• Use multifunction integrated devices when
  possible
• Talking aloud to yourself and team members helps
  spot errors
• If you find you made a mistake, figure out why.
• Solve the right problem.
• Act rather than react think ahead to prevent
  problems from cropping up
• Read the fine print at the bottom of data sheets.
• When in doubt, dont guess look it up and be
  sure
• Manage your time

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Model Simulate

• Where prototyping is impractical or expensive
• Verify design prior to implementation
• Avoid expensive mistakes
• Ensure that design will meet specifications
• Some design details easier to verify in
  simulation than on prototype
• Develop test for manufactured product

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Implement Prototype

• Implementation should follow naturally from
  previous design and modeling
• Determine order in which modules should be
  implemented, testing at each stage
• Plan ahead for tools needed for implementation
• Compilers/software tools
• Chip sockets, connectors, cables
• PC boards (through-hole vs. surface-mount, etc.)
• Test equipment

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Test Verification

• Develop a test plan early in the design stage
  incorporate testability features as necessary
• Test throughout design and implementation
• Test components independently, and then the
  integrated system functions
• Final test to verify meeting of specifications,
  as well as safety
• Ensure the product is user proof (test all
  external conditions/events)
• perhaps have non-designer test the product
• Production test detects manufacturing errors
  and defects not design errors

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General Troubleshooting
Define the problem Symptoms Extent
Analysis
What module could be causing the problem?
Synthesis
Evaluation Is this cause reasonable? Would
fixing it fix the problem?
Evaluation
Select the most likely cause of the problem
Decision
Action
Repair
Evaluation Problem solved? If not, check
another possible cause
Engineering Design, Alan Wilcox Pg. 39
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References

• Practical Engineering Design, Maja Bystrom
  Bruce Eisenstein, CRC Press, 2005
• Engineering Design for Electrical Engineers, Alan
  D. Wilcox, Prentice-Hall, 1990
• Computers as Components Principles of Embedded
  Computing Systems Design, Wayne Wolf, Morgan
  Kaufmann, 2001