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ECE 477 Design Review Team 02 Fall 2008 Outline • • • • • • • • • • 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 • • • • • • Microcontroller: PIC18F45K20 32 Kbytes Program Memory 36 I/O pins 14 10-bit AtoD channels Up to 64Mhz 5mA @ 20Mhz Component Selection Rationale • • • • • Accelerometers: MMA1212 & MMA2301 Limited choices +/- 250g sensitivity 5V power source Single axis Component Selection Rationale • • • • 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 • Use 9 channels of ATD conversion with 2 more used for reference voltage • 1 SPI used for SD interfacing • 2 TTL pins for RS232 interfacing • Operating Voltage: 3.3V • 8 MHz operating frequency • 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
