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What is Design?

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  1. 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”

  2. 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

  3. 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

  4. Common Graphical Ways to Describe the Design in More Detail • “Artist’s representation” • Used in sales and marketing to laymen. Rarely used in true engineering presentations. • Context Level Diagrams • Commonly appears as graphical overview of system’s 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 user’s 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

  5. 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.

  6. Typical “artist’s representation of the concept”for non-technical personnel(ignore the dimensions on the bulb) Control This representation is rarely used in Senior Design or real engineering presentations

  7. 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

  8. 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.

  9. Example of Use Cases Table

  10. 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 system’s logical architecture

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

  12. 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 system’s HW / SW architecture

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

  14. 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.

  15. Level 1 / 2 Exploded Architecture Diagram Software (PC) Interface Logic User Input Headlamp GUI Command Interface Message Transmitter Function call Command Data

  16. Level 1 / 2 Exploded Architecture Diagram Software (PC) Interface Logic User Input Headlamp Embedded Logic Controller Interface Circuit Enable[1:0] Low Voltage

  17. 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 Enable[1:0] Low Power Enable[1:0] High Power Headlamp

  18. Execution Flow Chart (diagram) Button Press Which Button? Send “High Off” Command Send “Low Off” Command Low High Off Send “Low On” Command Send “High On” Command Send “Low Off” Command Send “High Off” Command

  19. Data Throughput Diagram Telephone Encryption Device (different Senior Design project) Audio 4 KHz Bandwidth Audio 4 KHz Bandwidth Voice Anti-aliasing Filter Low-pass Filter Speech Analog Speech 2 KHz Center Audio 8 KHz cut off ADC DAC 8-bit words @ 8 KHz 8-bit words @ 8 KHz Block Compressor Block Decompressor 2-bit words @ 8 KHz 2-bit words @ 8 KHz Block Encrypter Block Decrypter Digital Cipher Text

  20. More Examples of Graphical Representations of Design From ECE Digital timing diagram

  21. More Examples of Graphical Representations of Design From ECE Signal / Data flow architecture block diagram Source: Webster, Biomedical Engineering

  22. More Examples of Graphical Representations of Design From ECE Design schematic diagram

  23. More Examples of Graphical Representations of Design From ECE Printed Circuit Board Schematic Diagram - Original Mac 512

  24. More Examples of Graphical Representations of Design From ECE Printed Circuit Board Schematic Diagram - Original Mac 512 (detail)

  25. More Examples of Graphical Representations of Design From ECE Printed Circuit Board Schematic Diagram

  26. More Examples of Graphical Representations of Design From ECE Printed Circuit Board Layout Diagram

  27. More Examples of Graphical Representations of Design From Comp. Sci. Software Data flow diagram

  28. Examples of Graphical Representations of Design From Allied Fields Chemical Engineering – “Flow Sheets”

  29. Examples of Graphical Representations of Design From Allied Fields Chemical Engineering – “Flow Sheets”

  30. Examples of Graphical Representations of Design From Allied Fields Hydraulic diagrams

  31. Examples of Graphical Representations of Design From Allied Fields Hydraulic diagrams

  32. Examples of Graphical Representations of Design From Allied Fields Optics - Ray tracing, assembly & mechanical motion drawings

  33. Examples of Graphical Representations of Design From Allied Fields Pneumatic system design of a commercial leak detector

  34. Examples of Graphical Representations of Design From Allied Fields Part Drawing (ie, detailed mechanical drawing) produced by AutoCAD

  35. Examples of Graphical Representations of Design From Allied Fields 3D - Mechanical assembly drawing of complicated optical system

  36. 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 won’t 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.

  37. 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

  38. Distinguishing Design from Implementation • Caution needed • Example#1: Should I buy a low or high performance op-amp • In many projects, this decision wouldn’t 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?