Transcript Introduction to Senior Design - George Washington University

The George Washington University
School of Engineering & Applied Science
Department of Electrical & Computer Engineering
ECE Senior Design
Design vs. Implementation
Professor Tom Manuccia
Lecture Agenda
• What is design
• Ways to describe design
• What is implementation
• With a running example
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
What is Implementation
• The process of defining how the design
blocks perform their functions and building
the actual design blocks to function according
to the design
• The “How” of your project
• The realization of the design
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.
An Example
• I want to control the headlights of my car with a
computer; I have a 1990 Nissan Maxima
• Start by building a proof of concept (POC)
• Requirements
– Turn low beam on and off
– Turn high beam on and off
– All control is through a standard PC
• Specifications
– 12Vdc, 100W Halogen Dual Beam Headlamp
– GUI with three buttons:
• OFF, LOW, and HIGH
Concept of the Example
Control
Design Example
User Input
Software
(PC)
Interface
Logic
Headlamp
Ways to Describe the Design
•
System Architecture (Design Blocks)
–
•
Describes functional blocks and how they interact
Data throughput analysis
–
•
Describes the data path and calculate the rate of data throughput at each
step to find the overall throughput
Execution Flow diagram
–
–
•
Illustrate the steps and decision points that the execution unit will follow
Your algorithm
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
Ways to Describe the Design
(Continued)
•
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.
System Architecture Example
GUI
Function call
Command
Interface
Command Data
Message
Transmitter
RS-232 Byte
Embedded
Logic Controller
Enable[1:0]
Low Voltage
Interface Circuit
Enable[1:0]
High Voltage
Headlamp
Data throughput analysis
PC
9600 bps
Embedded
Logic Controller
Execution Flow Example
Button Press
Send
“High Off”
Command
Send
“Low On”
Command
Low
Which
Button?
Off
Send
“Low Off”
Command
Send
“High Off”
Command
High
Send
“Low Off”
Command
Send
“High On”
Command
Use Cases Example
Scenario
User Input
System Response
#1
User clicks on a button
Headlamp responds
accordingly
Context 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
Context Level Diagram Example
User Input
System
State of
headlamp
Level One Design Diagram
• The first level of decomposition of the
project
• Describes the fundamental design blocks
and their interactions at the top level
• The most common form of describing the
system architecture
Level One Design Diagram
Example
User Input
Software
(PC)
Interface
Logic
Headlamp
Level N Design 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 schematics, pseudo
code, mechanical model, etc.
Level 1 Design Diagram
Example
User Input
GUI
Function call
Software
(PC)
Interface
Logic
Command
Interface
Headlamp
Command Data
Message
Transmitter
Level 1 Design Diagram
Example
User Input
Software
(PC)
Embedded
Logic Controller
Interface
Logic
Headlamp
Interface Circuit
Enable[1:0]
Low Voltage
Implementation Example
• Software written in Visual Basic 6.0
• GUI
• 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)
• Reed Relay
• Automotive Relay
• 120Vac to 12Vdc power Transformer
Implementation Example
PC
GUI
RS-232
CommandTx
CB-7520
RS-485
CB-7050
2 x Open Collector Outputs with 10 mA current
2X Reed Relay
2 x Circuit with 350 mA current
2X Auto Relay
2 x Circuit with 10A current
12VDC @ 10 A
120VAC @ 60Hz
Power Transformer
GND
Headlamp
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?
Logic vs. Physical
• Logically separate design blocks
– Have interfaces and functions
• Physical parts
– Can serve as implementations of logical blocks
• What is the mapping of the logical to the
physical?
• This is where design and implementation can
meet
An Example
• You want to build a real-time point-topoint telephone that uses encryption to
secure the channel
• There are only two phones in the
system
• One person calls the other, and the
channel is encrypted
Concept
Your Phone
Point A
Your Phone
Point B
Encrypted Link
Basic Needs
• Data Throughput (rate)
–
–
–
–
Raw sampling rate: 8 KHz @ 8-bits
Compression: ADPCM 2-bits per sample
Effective end to end rate: 64Kbps or 8KBps
Link rate: 16 Kbps or 2KBps
Architecture (Part 1)
Place Call
Answer Call
Call Request
Voice
Anti-aliasing
Filter
Call Request
Controller
Block
Compressor
ADC
Swing
Buffer
Block Encrypter
Transmitter
Link Data
Architecture (Part 2)
Place Call
Answer Call
Call Request
Call Request
Controller
Block
Decompressor
Link Data
Receiver
Swing
Buffer
Block Decrypter
DAC
Low Pass
Filter
Speech
Data Throughput
Audio 4 KHz Bandwidth
Voice
Audio 4 KHz Bandwidth
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
Implementation Options
• Microcontroller with CODEC
• FPGA with CODEC
Physical Implementation 1
(One Side)
Physical Implementation 2
(One Side)
FPGA
LED
Block
Compression
Transmitter
SM
Block
Encrypter
Transmitter
(serializer)
Block
Decrypter
Receiver
(deserilizer)
Block
Reconstriction
Receiver
SM
CODEC
(ADC)
(DAC)
Push-Buttons
RS-232
Line Driver
/
Receiver
LED
Push-Buttons