Andrew Phillips, Ben Laskowski, Shannon Abrell, Rob Swanson
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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
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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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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Op-Amps – LM324
 Operates from single 5v supply
 Low supply currents (700μA per amplifier)
 Low cost
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Current sense amp – INA148
 Inputs need not be referenced to circuit ground
 Large common-mode input voltage range
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External ADC – MCP3204
 Needed extra ADC channels
 This IC inexpensive and meets speed/resolution needs
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Battery Management Micro – PIC18F4423
 13 ADC channels w/ 12-bit resolution
 Easily obtained
 Mature technology (few silicon errata items)
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Main Micro – PIC32MX575F256L
 6 UARTs, product familiarity
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Wireless – XBee Pro 900MHz
 6 mile range, sufficient data transfer speed
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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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Battery Management
 Stand-alone package
 Plastic case provides
electric isolation
 Slots for battery leads
and serial line to main
controller
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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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Battery Micro
 Digitizes and scales
battery voltages via
simple code
 Integrates current flow
over time to obtain
battery charge
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External ADC
 Used to increase
number of ADC channels
available
 Interfaces to battery
microcontroller over SPI
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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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Power supply
 Converts 12V to 5V and
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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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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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XBee module
 Appears as serial port to
PIC32
 Hardware flow control
pins used to minimize
risk of buffer overflow
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LED Drivers
 TLC5917
 Similar to 74HC595 but
includes constantcurrent output drivers
 Ease PCB routing – 3
wire bus instead of 13
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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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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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Voltage followers
 Mostly uninterrupted
ground plane for noise
rejection
 Decoupling capacitor
very close to op-amps –
vital for stability
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Current monitor
 Completely
uninterrupted ground
plane
 Voltage reference IC and
decoupling caps very
close to op-amp
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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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Power supply
 Linear LDO regulator
 Expected power
dissipation ~100mW
 Bulk capacitor located
nearby for stability
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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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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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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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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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LED Drivers
 Located directly
underneath 7-segment
LED modules for
compactness
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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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EEPROM
 Located under PIC32 for
layout convenience and
to minimize length of
high-speed SPI traces
 Decoupling capacitor
nearby
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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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Main controller
 Began reading up on various microcontroller
features (DMA, interrupt mechanism)
 Installed and began experimenting with C
compiler
 Simple programs compile successfully
Item
Expected Completion Week
Order all remaining components
8
Complete design and order main PCB
9
Complete battery monitor software
10
Assembly of battery monitor boards
10
Complete battery monitor packaging
11
Main board software complete
13
Assembly of main board
13
Complete main package enclosure
14
Final integration
15