The George Washington University School of Engineering

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The George Washington UniversitySchool of
Engineering Applied ScienceDepartment of
Electrical Computer EngineeringECE Senior
DesignGraphical Representations of
Designa.k.a., More different types of block
diagrams than I ever knew existed
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What is Design?

• The process of translating the Requirements and
  Specifications into a well thought out plan that
  fully describes the system
• The What and Why of your project
• The high level blueprints of what you will build

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Example of a toy EE / Comp E Design

• I want to control the headlights of my car with a
  computer
• Simplified Requirements
• Must turn low beam on and off
• Must turn high beam on and off
• All control is through a standard laptop PC
• Simplified Specifications
• System will control 12Vdc, 100W Halogen Dual Beam
  Headlamps
• GUI will have three buttons
• OFF, LOW, and HIGH

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Common Graphical Ways to Describe the Design in
More Detail

• Artists representation
• Used in sales and marketing to laymen. Rarely
  used in true engineering presentations.
• Context Level Diagrams
• Commonly appears as graphical overview of
  systems interactions with the outside world in
  engineering presentations.
• Use cases
• Describes different scenarios of how the user can
  interact with the project
• For each different scenario, explain users input
  and the response of the system
• Functional Block Diagram
• Depicts the different logical functions that must
  be performed by your design and their
  interactions
• Architecture Block Diagram
• Describes how the logical functional blocks are
  mapped into hardware and software blocks.
  Depicts how these blocks interact.
• Data throughput analysis / diagram
• Describes the data path and states the rate of
  data throughput between each module consistent
  with the overall system throughput

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More Ways to Describe the Design(Continued)

• Execution Flow Chart (diagram)
• Depicts the inputs, steps, decision points
  outputs that the execution unit will follow
• The conventional, Computer Science flow chart
  representation of your algorithms
• Timing Diagrams
• For hardware modules it describes the details of
  the timing of the inputs and outputs of the
  module
• HCI (Human Computer Interaction) Mockups
• Describes the main points of the user interface,
  this includes GUIs and physical interfaces such
  as switches and displays
• 3-D Mechanical Drawings
• Describes the mechanical aspects of the design,
  the dimensions of the chasses and any other
  relevant information
• Interface Control Document
• Describes the verbose details of any interfaces
  to the device, i.e. the details of a data port,
  command set, etc.

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Typical artists representation of the
conceptfor non-technical personnel(ignore the
dimensions on the bulb)
Control
This representation is rarely used in Senior
Design or real engineering presentations
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Context Level Diagrams

• Presents the reader with the context in which the
  project exists
• Illustrates what interactions the system has with
  its surroundings
• Explains system level interfaces and their
  functions

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Context Level Diagram Example
PRW Lighting Control System
Single keystrokes by user on laptop
State of car headlamp Off, low, high
This representation is one of the most commonly
used in Senior Design and real engineering
presentations. In one glance it gives someone
completely unfamiliar with your project an idea
of what your system is going to do.
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Example of Use Cases Table
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Level One Functional Block Diagram

• Shows only logic and function (what the blocks
  need to do), not hardware or software
• Describes the fundamental logical design blocks
  and their interactions
• The first or top level of logical decomposition
  of the system into separate functions
• The most common form of describing the systems
  logical architecture

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Level One Functional Block Diagram
Interpret keystrokes
Computer Electrical interface
Headlamp
User Input
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Level One Architecture Block Diagram

• Each Level 1 functional block maps to one or more
  Level 1 hardware and software blocks.
• Describes the top level hardware and software
  design blocks and their interactions.
• The most common form of describing the systems
  HW / SW architecture

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Level One Architecture Block Diagram
GUI Software (laptop)
Interface Logic (hardware)
Headlamp
User Input
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Level N Architecture Diagram

• The result of further decomposition of the design
  
• Each step of the recursive process of design
• The next level of decomposition of the design
  block above in the design hierarchy
• Like the level one design diagram, describes the
  design blocks and their interactions
• Still the most common form of describing the
  system architecture
• Stops at the point where the function of a design
  block is so basic that any further decomposition
  would lead to individual components, pseudo code,
  mechanical components, etc.

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Level 1 / 2 Exploded Architecture Diagram
Software (PC)
Interface Logic
User Input
Headlamp
GUI
Command Interface
Message Transmitter
Function call
Command Data
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Level 1 / 2 Exploded Architecture Diagram
Software (PC)
Interface Logic
User Input
Headlamp
Embedded Logic Controller
Interface Circuit
Enable10 Low Voltage
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Overall System Architecture(fully exploded all
2 levels)
GUI
Command Interface
Message Transmitter
Function call
Command Data
RS-232 Byte
Embedded Logic Controller
Interface Circuit
Enable10 Low Power
Enable10 High Power
Headlamp
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Execution Flow Chart (diagram)
Button Press
Which Button?
Send High Off Command
Send Low Off Command
High
Low
Off
Send High On Command
Send Low On Command
Send Low Off Command
Send High Off Command
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Data Throughput Diagram Telephone Encryption
Device (different Senior Design project)
Audio 4 KHz Bandwidth
Audio 4 KHz Bandwidth
Anti-aliasing Filter
Low-pass Filter
Voice
Speech
Analog Speech 2 KHz Center
Audio 8 KHz cut off
ADC
DAC
8-bit words _at_ 8 KHz
8-bit words _at_ 8 KHz
Block Compressor
Block Decompressor
2-bit words _at_ 8 KHz
2-bit words _at_ 8 KHz
Block Encrypter
Block Decrypter
Digital Cipher Text
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More Examples of Graphical Representations of
Design From ECE
Digital timing diagram
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More Examples of Graphical Representations of
Design From ECE
Signal / Data flow architecture block diagram
Source Webster, Biomedical Engineering
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More Examples of Graphical Representations of
Design From ECE
Design schematic diagram
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More Examples of Graphical Representations of
Design From ECE
Printed Circuit Board Schematic Diagram -
Original Mac 512
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More Examples of Graphical Representations of
Design From ECE
Printed Circuit Board Schematic Diagram -
Original Mac 512 (detail)
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More Examples of Graphical Representations of
Design From ECE
Printed Circuit Board Schematic Diagram
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More Examples of Graphical Representations of
Design From ECE
Printed Circuit Board Layout Diagram
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More Examples of Graphical Representations of
Design From Comp. Sci.
Software Data flow diagram
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Examples of Graphical Representations of Design
From Allied Fields
Chemical Engineering Flow Sheets
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Examples of Graphical Representations of Design
From Allied Fields
Chemical Engineering Flow Sheets
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Examples of Graphical Representations of Design
From Allied Fields
Hydraulic diagrams
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Examples of Graphical Representations of Design
From Allied Fields
Hydraulic diagrams
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Examples of Graphical Representations of Design
From Allied Fields
Optics - Ray tracing, assembly mechanical
motion drawings
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Examples of Graphical Representations of Design
From Allied Fields
Pneumatic system design of a commercial leak
detector
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Examples of Graphical Representations of Design
From Allied Fields
Part Drawing (ie, detailed mechanical drawing)
produced by AutoCAD
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Examples of Graphical Representations of Design
From Allied Fields
3D - Mechanical assembly drawing of complicated
optical system
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Design vs. Implementation

• Design is generally block diagrams specs
• It is the abstract, planning part of the activity
• It contains those specs so critical that if not
  followed, the project will not be successful.
• Example Should I use the 1 MHz (10 Hz / deg C)
  crystal oscillator circuit from the ARRL handbook
  or the 1 MHz (1 Hz / deg C) crystal oscillator
  circuit from Horowitz and Hill?
• Implementation
• It is the part of a project when a design is
  reduced to practice.
• Implementation contains options that are equally
  viable in that they wont affect the overall
  performance or success of the project.
• Example Should I buy a 1 kohm, 1 watt resistor
  from Digikey or Allied?
• Example Should I use the 1 MHz (1 Hz / deg C
  drift) crystal oscillator circuit from the ARRL
  handbook or from Horowitz and Hill?
• Schematics and mechanical drawings can be either
  design or implementation depending on the
  importance of the decisions represented on them.

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Examples of Implementation

• Software written in Visual Basic 6.0
• The specifics of the GUI
• Specific software function definitions or
  prototypes commandTx( int buttonCode)
• Hardware
• CB-7520 (RS-232 to RS-485 Converter)
• CB-7050 (15-bit Digital I/O Module, 7-bit Input,
  8-bit Output)
• Specific Reed Relay
• Specific High Power Automotive Relay
• Specific 120Vac to 12Vdc power Transformer

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Distinguishing Design from Implementation

• Caution needed
• Example1 Should I buy a low or high performance
  op-amp
• In many projects, this decision wouldnt make any
  difference (other than cost). In this case it
  would be implementation.
• In other projects, the subsystem will not meet
  specs with a low-performance op-amp. In this
  case this decision would be part of the design
  process.
• Such decisions are often indicated on a schematic
  instead of in a block diagram, but if the choice
  is critical to success it is clearly part of the
  design process.
• Example 2 Should I power an op-amp from 5 v,
  plus and minus 5v, or plus and minus 15 volts?
• Example 3 Should I position my components and
  route the traces on my PCB in a particular way,
  or is this little more than an art left to a
  technician?