Concept
Motivation
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Tech Specs
Requirements
Architecture
Use Cases
System States
Risks
Error Handling
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TEAM 10: APOCALYPSE
Spring 2009

MEMBERS

Mark Hamilton
Rebecca Levin

PROJECT CONCEPT

A "black box" device for vehicles used to reconstruct an accident with data from GPS, accelerometers, force sensors, etc.

Some modern cars incorporate event data recorders that record some information about the car's sensors before a crash. However, we did not find any that incorporate accelerometer or GPS data and none of these devices are available aftermarket.

TECHNICAL SPECIFICATIONS

Hardware:

Atmel ATMega168 microcontroller at 20MHz
32 Channel GPS 5Hz receiver
3 Single-Axis Accelerometers (+\-200g)
Flexiforce Pressure Sensor
Breakout Board for SD-MMC cards
12V power source (from vehicle)

Software:

We will write all the software for the microcontroller in C. No existing software will be used on the microcontroller itself.

Protocols:

I2C (Accelerometer)
RS-232/NMEA 0183 (GPS)
SPI (SD Card)

PARTS

REQUIREMENTS

Reads data from 5Hz GPS receiver.
Reads data from a 3-axis accelerometer at a rate of at least 100Hz.
Reads data from up to four resistive force sensors at a rate of at least 100Hz.
Records sensor data to an SD card.
Continuously records at least the last 20 seconds of sensor datat to a buffer in a FIFO manner. Old data are overwritten once the buffer is filled.
If a crash event is detected, the data from the event are frozen in the buffer and are not overwritten.
The device must be powered from the vehicle's electrical system and must tolerate the noise and voltage fluctuations present in this power supply.
The device will contain a backup battery and will automatically switch to this power source if the power source from the vehicle is interrupted as could occur in a crash.
System will be small in size and easily mountable in a vehicle.

ARCHITECTURE

USE CASES (INTERACTION DIAGRAMS)

To be completed.

SYSTEM STATES & TRANSITIONS

RISKS & MITIGATION STRATEGIES

Sensor failure - If one of the sensors fails or the system loses communication with a sensor, it shall continue to read data from all remaining sensors and not crash. Furthermore, it will alert the user that an error has occurred via the display.
SD failure - If for some reason data cannot be written to the SD card, if a crash event occurs the system will record as much data as it can to the internal flash on the microcontroller. In this way the system can still provide useful data even if it cannot record to the primary storage device.
Power failure - The system will have a battery backup circuit that will provide power in the event of external supply failure.