Design Document

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Design Document

• The Design Document is a Joint Assignment of
  Senior Design I and Technical Writing

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General Engineering Process
Problem or Expression of Need
Design Constraints
Evaluation and Synthesis of Alternative Solutions
Elements of Approach
Analysis (perhaps including experimentation)
Decision (justification of selected solution)
Solution
Adapted from Salt Rothery, Design for
Electrical and Computer Engineers
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Design Document Components

• Executive Summary
• Problem
• Design Requirements
• Technical and Practical Constraints
• Approach
• Evaluation
• Summary of Future Work
• Acknowledgements
• References
• Appendices

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Design Requirement/Constraints

• Ref Voland, G., Engineering by Design. Addison
  Wesley, 1999
• Larry Hand, Peavey Electronics, 2000

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Proof of Concept?
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After Proof of Concept, What Next?

• Vacation
• Big Bonus
• Two Attaboys
• Another Project
• Technical Formulation, Physical Design, and
  Transition to Manufacturing

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A technical formulation takes an idea and
translates it to an engineering context, complete
with relevant objective technical and practical
design constraints and appropriate theory and
design methodologies needed to address the
design.  It translates a design idea into a set
of related, feasible engineering specific
problems.
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Constraints are a Good Thing

• Define the boundaries within which the search for
  solutions must be conducted
• Enhance the effectiveness of the design
• Avoid designs that are illegal or hazardous
• Make designs economically viable

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Types of Constraints or Specifications

• Can be broken down several ways
• Example Bus specification
• Physical (dimensions, connectors, pins)
• Functional (arbitration protocol, read cycle)
• Electrical (impedance, max/min signal levels)
• We will use
• Technical Design Constraints
• Practical Design Constraints

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Technical ConstraintsRequirements on which
technical aspects of the design hinges

• Signal tolerances (gt 30 duty cycle clock at 1MHz
  /-1)
• Supply current range (.5 mA min to 100 mA max)
• Power efficiency (83 supply efficiency at rated
  load)
• Speed (interrupt service latency lt 1 ?S)
• Conversion rate (12-bit conversion at
  500Ksamples/sec)
• Transmission distance (100 M with unobstructed
  view)
• Quantization error (,- 5mV)
• Frequency response (20 Hz to 20 KHz, /- 3 dB)
• Signal-to-noise ratio (50 dB min)

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Practical Design ConstraintsBroader issues
affecting designs success

• Economic
• Environmental
• Sustainability
• Manufacturability
• Ethical
• Health and Safety
• Social and Political

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Economic

• Limits on Production Cost
• Depreciation of Equipment
• Operating Cost
• Service or Maintenance Requirements
• Existence of Competitive Solutions in the
  Marketplace

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How is Cost Determined(Note that cost is NOT
price)

• Material Cost
• Labor Cost
• Manufacturing Burden
• Selling, General, and Administrative Expense
  (SGA)

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Example CaseHow Much does it Cost

• Material Cost --- 52 of Total Cost
• Unit Price Quantity for all (Bill of
  Materials) BOM items
• Labor Cost --- 8 of Total Cost
• Direct labor or value added labor required to
  manufacture the product

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How Much Does it Cost

• Manufacturing Burden --- 17 of Cost
• Indirect Labor
• Utilities
• Facilities
• Employee Benefits
• Depreciation, rent, etc..

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How Much Does it Cost

• Sales/General and Administrative -- 23
• Cost of Selling the Product
• Sales commission
• Advertising
• Service and Warranty
• Corporate Management
• Research and Development
• Bad Debt, etc..

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Environmental

• Temperature Ranges
• Moisture Limits
• Dust Level
• Intensity of Light
• Noise Limits
• Potential Effects Upon People or Other Systems

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Sustainability

• If you birth it, Its always your baby
• Customer complaints
• Obsolete sole-source Parts
• Warranty claims and field failures
• Specification changes in standard components

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Manufacturability

• Programs for Automated Assembly Equipment
• Axial Sequencer and Insertion
• Radial Insertion
• DIP Socket and IC insertion
• Surface Mount Chips, ICs, Odd Shaped Components
• Automated Test

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More things to consider

• Mechanical Design and Packaging
• Space Allocation or Dimensional Requirements
• Weight
• Material Characteristics
• Power Requirements
• Protect Unit During Shipment
• Attractive at Point of Sale
• Advertising
• OEM or Consumer packaging

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Legal

• Governmental Safety Requirements
• Environmental or Pollution Control Codes
• Production Standards

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Health and SafetyHuman Factors/Ergonomics

• Users Characteristics
• Strength
• Intelligence
• Anatomical Dimensions
• Visual Acuity
• Hearing Discrimination
• Reaction Time
• Reading Skills

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Social and PoliticalAgency Approvals

• UL
• CSA
• FCC
• NOM
• CE
• NEMKO
• DEMKO

• VDE
• IRAM
• SASO
• SANZ
• SAA
• JIS
• and more.....

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Sources of Engineering Standards

• Companies
• Engineering Societies
• Governments (U. S., others)
• Special Interest Groups
• Federations of Private and Public Interests
  (American and International)
• Independent Laboratories

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ExamplesSee http//www.dma.org/rohrers/subject/s
tandorg.htm for extensive list of links

• ACM (Association of Computing Machinery)
• AES (Audio Engineering Society)
• ANSI (American National Standards Institute)
• EIA (Electronic Industries Association)
• ESD (Electrostatic Discharge Association)
• IEEE (Institute of Electrical and Electronics
  Engineers)

• ISO (International Standards Organization)
• ITU (International Telecommunications Union)
• OSHA (Occupational Safety Health
  Administration)
• PCI SIG (PCI Bus Special Interest Group)
• UL (Underwriters Laboratories)
• USB Developers (Universal Serial Bus Developers
  Forum)

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How Design Approach Relates to Design Description
Elements of Approach
Functional Overview
Design Description
Background Theory
Design Tradeoffs
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Block Heater ExampleGeneral Problem Constraints

• Sometimes automobile block heaters power sources
  are dead (unpowered)
• Sometimes heaters burn out (open)
• Heaters use120-Volt Power at 300 to 400 Watts
• Want indicator in extension cord to warn uses of
  potential problems (then could set breaker or run
  car during day)

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Block Heater ExampleEngineering Problem

• Design detection device integrated into extension
  cord
• Detect difference between 0.5 and 3.0 amperes
• Present binary conclusion to user
• Consume less than 5W
• Integrated manufacturing cost less than 6

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Block Heater ExampleApproach

• Functional Overview
• Diagram of System
• Broad description of needed functionality
• Background and/or Theory
• Types of binary indicators
• Implications of including in extension cord
• Possible Designs Evaluation of Alternatives
• Series indicator design
• Transformer coupled design
• Switch activated design
• Detail Design Description

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Block Heater ExampleFirst Approach, First Attempt
1 ohm
Analysis reveals that LEDs must carry 4 amperes
of forward current not practical due to LED cost
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Block Heater ExampleFirst Approach, Second
Attempt
More analysis using flux equation reveals
realistic solution
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Block Heater ExampleSecond Approach, First
Attempt
Alternate working solution found. Even though it
cost less is rejected because switch would have
to be depressed (not hands-free operation)
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Evaluation of Alternatives

• Design Constraints the yardstick against which
  alternatives are evaluated
• Cost and performance usually the main factors
• Solution will be near optimal (never perfect)
• Other issues are reliability, maintainability,
  sustainability, manufacturability, time to
  market, etc.

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Design Methodologies Used in Approach

• Choice of methodology will depend on project
  specifics
• Objective is to identify the best solution with
  minimum engineering cost
• Usually involves triangulation to develop
  confidence in design
• Analysis
• Simulation
• Experimentation

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Summary of Approach Components

• Functional Overview
• Theory Background
• Synthesis of Design Options
• Analysis of Options
• Justification of Design Decision
• Detailed Design Description