Transcript Design Review

ECE 477 Design Review
Team 02  Fall 2008
Outline
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Project overview - K
Project-specific success criteria -K
Block diagram -K
Component selection rationale -A
Packaging design -A
Schematic and theory of operation -M
PCB layout -D
Software design/development status -K
Project completion timeline -A
Questions / discussion
Project Overview
• Alleviate risks by providing a cushion
between the player’s head and the world
• Real time monitoring of player impacts
• Hardware in high stress environment
• Keeping player happy while improving
functionality of an old tool
Project-Specific Success Criteria
• An ability to recharge and monitor an
integrated (lithium ion) battery.
• An ability to sense impact data using 3-D
accelerometers.
• An ability to alert sideline personel when a
dangerous hit is received.
• An ability to log/timestamp impact data on a
removable memory device (SD card).
• An ability to remotely monitor real-time impact
data and tune impact detection thresholds via
an embedded web server.
Block Diagram
Component Selection Rationale
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Microcontroller: PIC18F45K20
32 Kbytes Program Memory
36 I/O pins
14 10-bit AtoD channels
Up to 64Mhz
5mA @ 20Mhz
Component Selection Rationale
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Accelerometers: MMA1212 & MMA2301
Limited choices
+/- 250g sensitivity
5V power source
Single axis
Component Selection Rationale
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Wi-Fi: Matchport
Limited choices on wireless protocol.
Flexible antenna
Embedded webserver
Packaging Design
• Weight…
– Helmet: 8 lbs + circuit
• Safety…
– Avoid cutting into helmet
– Cut into padding
• Performance…
– Antenna routed near surface
– Multiple PCBs
Packaging Design
• PCB Interconnects
– 100mil right angle pins
– Twisted Pair Ethernet Wiring
4 twisted pair
shielded
Packaging Design
• PCB Placement
– Avoid the front of the helmet
– Exact PCB placement unknown
• Spread around accelerometer boards
Schematic/Theory of Operation
Microchip MCP73838 Charge Manager
• USB or AC input
Texas Instruments TPS75733 LDO
• 3.3V output, 5V input
• Up to 3A output current
Linear Technology LT1303 Boost
• Operating voltage: 2.5-4.2 volts
• 5V output
Linear Technology LTC3440 Buck Boost
• Operating voltage: 2.5-4.2 volts
• 3.3V output
Maxim DS2740 Fuel Gauge
• Operating voltage: 2.7-5.5V
• Single-wire interface
Schematic/Theory of Operation
PIC18F45K20 Microcontroller
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Use 9 channels of ATD
conversion with 2 more used
for reference voltage
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1 SPI used for SD interfacing
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2 TTL pins for RS232
interfacing
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Operating Voltage: 3.3V
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8 MHz operating frequency
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1.6-12 mA
Schematic/Theory of Operation
Accelerometers
• Freescale MMA1212 and MMA2301
Accelerometers
 x-axis and z-axis
• Operating voltage: 5 V
• Operating Current: 3-6 mA
• Analog output between 0.5V and 4.5V
Matchport b/g Wireless Adapter
• Operating voltage: 3.3 V
• Operating Current: 20-223 mA
• Connected to microcontroller via
RS232
• Embedded web server
Schematic/Theory of Operation
Microcontroller Schematic
Schematic/Theory of Operation
Power Supply Schematic
Schematic/Theory of Operation
Accelerometer Schematic
This single schematic is replicated three times in the design
Schematic/Theory of Operation
WiFi Schematic
Schematic/Theory of Operation
microSD Schematic
PCB Layout
• 7 PCBs with 5 unique layouts
– Power
– Microcontroller
– SD Card
– Wi-Fi
– 3x Accelerometer
• Trace width
– Mostly 12 mil
– Up to 50 mil for power
PCB Layout
• Power Management
Wall Wart
5V
SD PCB
Power PCB
DC LDO
Battery
3.3V 660mW
2.5-4.4V
1144mW
3.3V Micro PCB
66mW
5V
2.5-4.4V
1320mW
3.3V
MatchPort
5V
90mW
5V
90mW
Accel PCB
5V
90mW
Accel PCB
Accel PCB
SD PCB
• Fairly Simple
• Header and micro SD
holder
Accelerometer PCB
• Short data
traces
• Data routes
away from
Power
routes
• Similar
length data
routes
• 1k Resistors
• Bypass
capacitors
Power PCB
• Battery off board
• Zener diode switch
Wi-Fi PCB
• Mounting Brackets
• Passive circuitry on
bottom
• Separate dedicated
power
• Bulk Capacitor
Microcontroller PCB
• Power apart
from Digital
• Single source
ground
• Ground planes
under U28
• Bypass
capacitors
• Filter capacitors
• Bulk capacitor
• Short data
traces
• Micro clocked
slower than
max to reduce
noise
Software Design/Development Status
• Algorithm design
– Need an algorithm for computing the
moment and rotational force of 3 vectors
Project Completion Timeline
• Villanova’s Timeline
• Parts in soon!
• Coding to begin week of October 20th
Questions / Discussion