ECE 477 Design ReviewTeam 4 Fall 2010

(L to R) Andy Sydelko, Chris Cadawallader, Mike Wiliams, Craig Pilcher

Outline

Project overviewProject-specific success criteriaBlock diagramComponent selection rationalePackaging designSchematic and theory of operationPCB layoutSoftware design/development statusProject completion timelineQuestions / 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: 3741 so far in 2010 alone

Our goal is to prevent as many deaths as possibleIf the caretaker cannot be warned, the child protection system will try to act on its ownExtensible, 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 portAn ability to determine the presence of a child in a safety seatAn ability to use multiple safety seats in one vehicleAn ability to sound an audible alarm when the ignition is turned offAn 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 availableMultiple CAN ports, PWM for audio output, ATD converters, dual SCI ports, timers, etc.

Large amounts of available flash (512KB) for audio sample storageControllable 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 supportLong range (up to 1km), allows the use of small, inefficient antennasTransmitter only powered when sending switch statesCritical for battery-powered child sideReceiver enters low-power polling state when not receiving

Transceiver/Encoder pair operate with a microcontollerExtra input pins for future expansion8 inputs = 256 possible status messages

Packaging Design – Car Side

Car side box contains:

16-pin OBD-II cableRS-232 connectorTwo 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 deviceTo be replaced for integration with specific devicesChild side box must have access for battery replacement

General Schematic/Theory of Operation

2 CAN ports – Vehicle communicationHigh-speed CAN compatibility for vehicle state detection and unusual vehiclesSingle-wire CAN for peripheral control, such as windows, alarm, etc.2 SCI ports – RS232 (debugging) and RF RX2 ATD – Car state detection for older OBD-II protocolsPWM – Audio Output11 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 importantAccurate clock sources are important for high-speed CAN communicationExtensive debugging access and expandabilityNeed multiple power supplies:–5V for most chips

–3.3V for RF decoder

–12V for SWCAN transceiver

Child Side Layout - General Considerations

Two boards completedImportant considerationsRemove ground plane from AntennaBring extra inputs to headers for expanding system

Future improvements:Debounce learn switchMake sure to bring VccChange antenna drill hole sizes

Microcontroller Layout Considerations

Very specific oscillator layout required for accurate crystal operation.

–Current layout should exceed Freescale recommendationsExtensive 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 antennaNo planes or traces under the decoder or antenna

–Ground plane recommended for the receiverReceiver requires very clean, 3.3V power supplyDesigned to operate from a battery with no bypass capacitorsUtilizes 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- PWM audio output test

- CAN debugging routines

- Generic digital port dumps

- ATD converter test

Operational Software- Detection of cars on older

protocols completed

- 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 / DiscussionQuestions / Discussion