ece 477 design review: team 2 fall 2010
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ECE 477 Design Review: Team 2 Fall 2010. Andrew Phillips, Ben Laskowski , Shannon Abrell , Rob Swanson. Outline. Project overview Project-specific success criteria Block diagram Component selection rationale Packaging design Schematic and theory of operation PCB layout - PowerPoint PPT PresentationTRANSCRIPT
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ECE 477 Design Review:Team 2 Fall 2010
Andrew Phillips, Ben Laskowski, Shannon Abrell, Rob Swanson
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Outline Project overview Project-specific success criteria Block diagram Component selection rationale Packaging design Schematic and theory of operation PCB layout Software design/development status Project completion timeline Questions / discussion
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Project Overview
eV-TEK, or Telemetry for Electric Karts, is a tool for collecting and transmitting electric go-kart parameters in a race situation.
The collected data can help the driver and pit crew optimize vehicle performance and ultimately win races.
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Project-Specific Success Criteria An ability to report the approximate
number of laps remaining on a given battery charge
An ability to detect and report cell voltage anomalies
An ability to sense and display kart speed
An ability to track the number of laps completed
An ability to log and display vehicle telemetry data
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Block Diagram
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Component Selection Rationale Op-Amps – LM324
Operates from single 5v supply Low supply currents (700μA per amplifier) Low cost
Current sense amp – INA148 Inputs need not be referenced to circuit ground Large common-mode input voltage range
External ADC – MCP3204 Needed extra ADC channels This IC inexpensive and meets speed/resolution
needs
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Component Selection Rationale, cont’d Battery Management Micro –
PIC18F4423 13 ADC channels w/ 12-bit resolution Easily obtained Mature technology (few silicon errata items)
Main Micro – PIC32MX575F256L 6 UARTs, product familiarity
Wireless – XBee Pro 900MHz 6 mile range, sufficient data transfer speed
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Packaging Design
Main Packaging Aluminum Aerodynamic Sits in front of
driver on roll cage Detachable
faceplate holds main board
Driver displays Wiring connection
at rear
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Packaging Design
Battery Management Stand-alone
package Plastic case
provides electric isolation
Slots for battery leads and serial line to main controller
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Schematic/Theory of Operation Voltage Follower
Acts to increase input impedance of ADC channels
Allows the use of large divider resistor values for low current drain
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Schematic/Theory of Operation Battery Micro
Digitizes and scales battery voltages via simple code
Integrates current flow over time to obtain battery charge
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Schematic/Theory of Operation External ADC
Used to increase number of ADC channels available
Interfaces to battery microcontroller over SPI
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Schematic/Theory of Operation Main
microc0ntroller Can run up to
80MHz = 80MIPS Collects and
processes data from battery packs and sensors; logs; transmits to pit area
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Schematic/Theory of Operation Power supply
Converts 12V to 5V and 3.3V
High-efficiency switchmode regulator for 12->5V conversion
Linear LDO for 5->3.3V
Maximum power dissipation ~2.4W
Large copper pours on PCB for heatsinking
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Schematic/Theory of Operation Optical isolation
Battery monitors float with respect to main control board
1kV of isolation provided; we require ~50V of isolation
Servo motors also isolated “just in case”
Side benefit: 3.3V<->5V conversion
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Schematic/Theory of Operation XBee module
Appears as serial port to PIC32
Hardware flow control pins used to minimize risk of buffer overflow
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Schematic/Theory of Operation LED Drivers
TLC5917 Similar to 74HC595
but includes constant-current output drivers
Ease PCB routing – 3 wire bus instead of 13
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Schematic/Theory of Operation USB-Serial
converter Makes USB appear
as UART for PIC32 Eases software, PCB
layout Mature product,
most errata fixed by manufacturer
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Schematic/Theory of Operation DataFlash IC
2MB EEPROM-like device for data logging
Simple SPI interface; faster and more versatile than SD card
Data made available for download via USB interface
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PCB Layout – Battery Monitors Voltage followers
Mostly uninterrupted ground plane for noise rejection
Decoupling capacitor very close to op-amps – vital for stability
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PCB Layout – Battery Monitors Current monitor
Completely uninterrupted ground plane
Voltage reference IC and decoupling caps very close to op-amp
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PCB Layout – Battery Monitors Digital
components Separated from
analog components As many extra
micro pins as practical padded out
Decoupling capacitors as close as practical to each power pin
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PCB Layout – Battery Monitors Power supply
Linear LDO regulator
Expected power dissipation ~100mW
Bulk capacitor located nearby for stability
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PCB Layout – Main Board
Microcontroller Decoupling
capacitors located physically and electrically close to chip
Every pin is padded out for debugging and/or expansion
Pads provided for precision oscillator module, though it should not be required
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PCB Layout – Main Board
Power supply Switching regulator
is on top of continuous ground plane, and high dI/dt nodes are very short
Linear regulator has many vias to copper plane for heatsinking
Sufficient capacitance nearby for low ripple
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PCB Layout – Main Board
Optical Isolation Physically separate
from most other critical interfaces
Keepout areas near battery connectors – physical isolation is several times what is required
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PCB Layout – Main Board
Xbee Antenna connection
is as far from other components as possible
Capacitor located nearby to provide current pulses during RX->TX mode switches
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PCB Layout – Main Board
LED Drivers Located directly
underneath 7-segment LED modules for compactness
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PCB Layout – Main Board
USB UART Trace length from
USB connector is minimized to preserve differential nature of bus
Decoupling capacitors located as close as possible
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PCB Layout – Main Board
EEPROM Located under
PIC32 for layout convenience and to minimize length of high-speed SPI traces
Decoupling capacitor nearby
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Software Design/Development Status Battery monitors
Software is essentially done Need mechanism to calibrate
measurements▪ Preliminary tests indicate this will be easy
Roughly 400 lines of well-commented assembly code
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Software Design/Development Status Main controller
Began reading up on various microcontroller features (DMA, interrupt mechanism)
Installed and began experimenting with C compiler
Simple programs compile successfully
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Project Completion TimelineItem Expected Completion WeekOrder all remaining components 8Complete design and order main PCB
9
Complete battery monitor software 10Assembly of battery monitor boards 10Complete battery monitor packaging 11Main board software complete 13Assembly of main board 13Complete main package enclosure 14Final integration 15
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Questions / Discussion