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ECE 477 Design Review
Team 4  Fall 2010
(L to R) Andy Sydelko, Chris Cadawallader, Mike Wiliams, Craig Pilcher
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
Project Overview - Motivation
“A child safety-system that prevents parents and caretakers
from accidentally leaving children in vehicles.”
Average number of U.S. child hyperthermia fatalities per
year since 1998: 37
41
so far in 2010 alone
Our goal is to prevent as many deaths as possible
If the caretaker cannot be warned, the child protection
system will try to act on its own
Extensible, could be modified for other uses, e.g. pets or
seat belt verification on a school bus
Project Specific Success Criteria
An ability to determine the operating state of the vehicle
via the OBD-II port
An ability to determine the presence of a child in a safety
seat
An ability to use multiple safety seats in one vehicle
An ability to sound an audible alarm when the ignition is
turned off
An ability to interface directly to the internal vehicle CAN
Block Diagrams – Car Side
Block Diagram – Child Side
Component Selection Rationale - Micro
Extensive onboard peripherals are available
Multiple CAN ports, PWM for audio output, ATD converters, dual SCI
ports, timers, etc.
Large amounts of available flash (512KB) for audio
sample storage
Controllable power consumption
–Effectively battery powered when the car is off
Cost – expensive, but perfect for this stage
–Eventual goal is to scale down to the smallest 9S12(X) that handles all
peripheral, total audio samples, and speed requirements
Component Selection Rationale – RF XCVRs
Built-in pairing support
Long range (up to 1km), allows the use of small,
inefficient antennas
Transmitter only powered when sending switch states
Critical
for battery-powered child side
Receiver enters low-power polling state when not receiving
Transceiver/Encoder pair operate with a microcontoller
Extra input pins for future expansion
8 inputs = 256 possible status messages
Packaging Design – Car Side
Car side box contains:
16-pin
OBD-II cable
RS-232 connector
Two buttons (learn, reset)
Two LEDs (power, learning)
Speaker
Also needs to mount easily under
dash or near OBD-II port
Child Side
Child side box will have 1
LED (power) and 1 button
(learn) and a port for child
detection device
To be replaced for
integration with specific
devices
Child side box must have
access for battery
replacement
General Schematic/Theory of Operation
2 CAN ports – Vehicle communication
High-speed
CAN compatibility for vehicle state detection
and unusual vehicles
Single-wire CAN for peripheral control, such as windows,
alarm, etc.
2 SCI ports – RS232 (debugging) and RF RX
2 ATD – Car state detection for older OBD-II protocols
PWM – Audio Output
11 GPIO – Control lines/DEBUG/DEC data, switch inputs
RF Decoder
Decoder polls receiver to check for any
incoming packets
Baud rate tied to ground, same as encoder
High transmission speed is irrelevant
Digital outputs routed directly to
microcontroller
Learn button is now debounced through the
microcontroller, which also allows the
micro to track if we are in the “Learning
state” and activate an audio confirmation
when a seat is added.
SWCAN Transceiver
Sits on SWCAN bus, speed
controlled via microcontroller
Circuitry simply as required by
the transceiver
Powered by the cars battery
directly
Can enter sleep mode where it is
woken by SWCAN activity
Responsible for rolling down
windows, activating panic on
most vehicles
Child Side – Theory of Operation
Child Side – Theory of Operation
- Encoder sends button events to the transmitter
- All button events tied to send function
- Reduces power consumption to only when transmitting
- “Change ID” button for the one in 2^20 chances of a
conflict (probably useless)
- Encoder connected directly to transmitter, power down line
keeps transmitter off when buttons not being pressed
- Status indication LED shows when ID generation is taking
place
Car Side Layout – General Considerations
RF Isolation is important
Accurate clock sources are
important for high-speed CAN
communication
Extensive debugging access
and expandability
Need multiple power supplies:
–5V for most chips
–3.3V for RF decoder
–12V for SWCAN transceiver
Child Side Layout - General Considerations
Two boards completed
Important considerations
Remove ground plane from
Antenna
Bring extra inputs to headers for
expanding system
Future improvements:
Debounce learn switch
Make sure to bring Vcc
Change antenna drill hole sizes
Microcontroller Layout Considerations
Very specific oscillator layout
required for accurate crystal
operation.
–Current layout should exceed
Freescale recommendations
Extensive bypass capacitors
needed for power supplies,
PLL, voltage reference for
ATD converters, and internal
2.5V supply.
PCB - RF and Power Supply Considerations
Short, low-impedance connection to the
antenna
No planes or traces under the decoder or
antenna
–Ground plane recommended for the
receiver
Receiver requires very clean, 3.3V power
supply
Designed to operate from a battery with no
bypass capacitors
Utilizes input filtering and resistance to
reduce and clean supply to necessary levels
•Linear regulator chosen on car-side as a
result of noise considerations
Software Design/Development Status
Test Software Features
Operational Software
- PWM audio output test
- Detection of cars on older
protocols completed
- CAN debugging routines
- Generic digital port dumps
- ATD converter test
- Tracking of child seats state
working with ID reception
- Vehicle status state machine that
integrates multiple protocols
and seat tracking working
- Audio output not start
- Vehicle action via CAN not
started
Project Completion Timeline
Task
Timeline
Final PCB Layout Check
October 20, 2010
PCB Fabrication
~November 1
Car Detection Software via ATD
October 22
CAN Decoding Software
October 29
Audio Warning System Software
November 5
PCB Testing
November 16
Packaging
December 1
Questions / Discussion