Transcript ECE 477 Final Presentation Group ?? Fall 2004

ECE 477 Final
Presentation
Group 8  Fall
2004
Outline
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Project overview
Block diagram
Professional components
Design components
Success criteria demonstrations
Individual contributions
Project summary
Questions / discussion
Project Overview
• Objective: To design and build a shopping
cart capable of following a shopper around a
store
– Shopper carries an ultrasonic beacon
– Cart follows beacon by maintaining fixed
signal strength (within a small range)
– Infrared sensors mounted on cart enable it
to avoid obstacles
Block Diagram
Sharp
GP2D15
IRQ
PWM
Motor
1
PWM
Motor
2
Atmel
ATMega32L
Sharp
GP2D15
IRQ
A/D
Ultrasonic
Receiver 1
A/D
Ultrasonic
Receiver 2
Professional Components
• Constraint analysis and component selection
rationale
• Patent liability analysis
• Reliability and safety analysis
• Ethical and environmental impact analysis
Constraint Analysis
• Microcontroller Constraints:
– Moderate clocking speed (1 – 4 MHz)
– Modest space constraints
– Peripheral requirements
• A/D Converter
• RTI/Timer module and PWM
• External Interrupts
– Power and cost efficient
Constraint Analysis
• Microcontroller Candidates:
– Rabbit / PIC: Did not offer required
combination of peripherals
– HC05 / HC11: One-time programmable
memory
– MC9S08GT32 / ATMega32L: Identical
feature set – Atmel chip was chosen
due to ready availability of
development tools
Constraint Analysis
• Infrared Proximity Sensor
– Prime candidates were Sharp GP2D12 and
Sharp GP2D15 (analog vs digital)
– Chose GP2D15 – digital output was more
convenient and did not tie up A/D
• DC Motor
– Fast enough to keep up with a person
– Sufficient torque to power 6lb. cart
– Jameco 10:1, 600RPM,12V DC
geared motor
Patent Liability Analysis
• Using Sensors to track / locate objects
– US Pat # 5,165,064
• Uses array of ultrasonic transducers to locate a beacon
– US Pat # 5,491,670
• Uses multiple ultrasonic beacons to triangulate position
– US Pat # 6,567,044
• Uses sensors to determine location
• All cause problems under doctrine
of equivalents. First is also literal
Patent Liability Analysis
• Other Patent Liability issues
– US Pat # 4,751,658
• Uses sensors to avoid obstacles
– US Pat # 5,911,767
• Has a central control that uses sensor data to determine
future action
– US Pat # 4,710,020
• Uses sensors to determine distance of a transmitter
• The first is a literal infringement
rest are infringements under the
doctrine of equivalents
Reliability/Safety Analysis
• Reliability Drivers:
– Heat : Increased heat increases unreliability
– Component Derating: Prevents wear out
• Product Specific Drivers:
– Low power microcontroller, good ventilation,
lowers unreliability caused by heat
– High current through motors
and IR leads to non-derated
power chips
Reliability/Safety Analysis
• Components have failure rates of the order
of 10E-6 or better
• Acceptable for a non-critical application
• Components analyzed for failure:
– ATMega32L – 4.29E-6 fails
– Max663 – 3.336E-6 fails
– IRL530N – 4.795E-6 fails
Reliability/Safety Analysis
• FMECA– 5 major blocks: U/S transmitter, U/S receivers, IR
sensors, Motor drive circuitry, Power circuitry
– Critical reliability problem - potential collision with
user:
• Motors stuck on
• Defective IR sensors
– Both components well derated,
and should not fail, leading to high
overall safety of cart.
Ethical/Environmental Analysis
Environmental Impact
• Manufacture of semiconductors
– Environmentally unfriendly
• Soldering on PCBs
– Exposure to lead
• Plastic casing
– Recyclable
Ethical/Environmental Analysis
Environmental Impact
• Electricity
– Precious resource used
• Battery Disposal
– Careful and correct disposal needed
Ethical/Environmental Analysis
Ethical Impact
• Safety
– Warning labels
– Documentation
– Safety mechanisms
• Reliability
– Perform as stated in user manual
Design Components
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Packaging design considerations
Schematic design considerations
PCB layout design considerations
Software design considerations
Packaging Design
• Board mounted on bottom tray
• Board dimensions - 4” x 6”
• Motors with wheels attached mounted at
bottom – front wheel drive
• Two ultrasonic sensors mounted at front end
• Two infrared sensors mounted at
front corners
Packaging Design
• Cart only moves forward
– IR sensors only needed at front two
corners
– Ultrasonic sensors placed strategically to
allow determination of beacon bearing
• Back wheels are freely rotating caster wheels
– Provides for smaller turning radius
Packaging Design
• Beacon carried by shopper
– Small and light
• Circuit may be damaged/tampered with
– All circuitry hidden
• Storage space must be maximized
– No components placed in cart
• Batteries must be accessible
– Batteries not hidden
Schematic Design
• Main
Schematic
– Headers
for all
sensors
– Motor
control
MOSFETs
– IR input
inverted
Schematic Design
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Cart Power
Supply
– Power:
9.6V
– 6V rail
– -6V rail
– 3.3V
rail
Schematic Design
• Transmitter
– Max 663
– 12 V
battery
– 555 timer
Schematic Design
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Receiver
– LF353 op
amps
– Gain of 90
– Filter for
noise
PCB Layout Design
• 5 PCBs – 1 U/S Transmitter, 3 U/S Receivers, 1 Main
Board.
• Need modular layout to enable cutting of single
board.
• Noise immunity:
– Bypass capacitors close to microcontroller and
noise suppression capacitors between power and
ground at intervals
– Need wide, short traces to reduce
inductance, thereby reducing current
spikes and noise.
PCB Layout Design
• Noise Immunity:
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– No 90 angles minimize wave reflections
which lead to noise and radiation
– Reduce interference between sub-circuits,
by placing individual power and ground in
parallel
– High current motors need to be isolated
from rest of circuit, powered
directly from battery
– Copper pour
PCB Layout Design
Receivers
Transmitter
Main board
Software Design
• 32Kb flash, 2Kb SRAM – EEPROM not used
• Application code is organized in a commanddriven fashion
– Ultrasonic receivers are polled periodically
– Infrared sensors generate interrupt
requests
– Main loop reads voltage samples
and adjusts motor speeds
Software Design
Start
Main loop
Flowchart
Initialize on-board peripherals
Enable global interrupts
Read the last sampled
front left, and front
right voltages
Is left or right
voltage nonzero?
Y
Motor speed duty cycles
= (255 – Voltage) * 1.5
Turn off both
motors
N
Software Design
Periodic
Interrupt
Service
Routine
Start
Start
Clear the
interrupt flag
Clear the
interrupt flag
Read left receiver
Turn off opposite
motor
Read right receiver
Adjust motor on
same side
Store voltage samples
in global data
structure
Disable ultrasonic
receiver polling
Return
Return
External
Interrupt
Service
Routine
Success Criteria Demonstrations
1. Ability to generate a beacon signal - demo
2. Ability to identify the bearing of the beacon
- demo
3. Ability to approximate the distance to the
beacon using relative signal strength demo
4. Ability to follow the beacon - demo
5. Ability to avoid obstacles in the
path of motion - demo
Individual Contributions
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Team Leader – Aliasgar Poonawala
Team Member 2 – Raghuram Ramanujan
Team Member 3 – Clive Lopez
Team Member 4 – Mohan Rokkam
Team Leader – Aliasgar Poonawala
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Packaging design
Ethical and environmental impact analysis
Software debugging
Component selection
Member 2 – Raghuram Ramanujan
• Design constraint analysis and component
selection
• Software design
– Wrote diagnostic routines
– Devised control algorithm and wrote core
software modules
• Hardware design
– Microcontroller interfacing
– Infrared sensor interfacing
• Hardware debugging
Member 3 – Clive Lopez
• PCB layout design
• Hardware design
– Designed (and redesigned) ultrasonic circuits
– Microcontroller interfacing
• Hardware debugging
• Soldering and population of board
• Reliability and safety analysis
• Component selection
• Packaging
Member 4 – Mohan Rokkam
• Hardware design
– Ultrasonic circuitry
– Microcontroller interfacing
• Created and maintained webpage
• Hardware debugging
• Soldering and population of board
• Schematic design
• Patent liability analysis
• Component selection
• Packaging
Project Summary
• Important lessons
learned
– Fuses!
– Use bypass
capacitors
– Effective time
management
– Trust team mates
• Important skills learned
– OrCAD Capture and
Layout
– Soldering techniques
– Power supply design
– Ability to interpret
datasheets
Project Summary
• Second iteration enhancements
– Better control algorithm
– Better noise immunity for sensors
– Ability to send different instructions via
beacon
– Support for multiple carts
– Better beacon range
– Additional sensors
Questions / Discussion