ECE4894 Final Project

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ECE4894 Final Project

• Huy Nguyen (gtg963m)
• Toni Popovic (gtg338u)
• Keith Elkins (gtg758t)

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Sensor Accelerometer

• Accelerometers are sensors for measuring,
  displaying ,and analyzing acceleration
• Can be used alone or in conjunction with a data
  acquisition system
• Important features of accelerometers
• Acceleration amplitude range measured in Gs
• Ambient conditions temperature range and shock.

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Brief History of Accelerometers

• 1967 - ICP (Integrated-Circuit-Piezoelectric)
  sensors developed and marketed
• 1973 - The first rugged, industrial-grade, ICP
  accelerometer produced
• 1984 - Silicon capacitive sensors in volume
  production
• 1987 - Automotive accelerometer technology
  development started
• 1991- Analog Devices introduced its first MEMS
  device, a single-chip accelerometer used for
  airbag deployment
• Present Increasing demand and applications for
  accelerometers

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ADXL105 Accelerometer

• Single axis accelerometer
• High performance and high resolution ( 2 mg)
• 1000 g Shock Survival
• Small size 0.4 cm3
• Low power consumption
• Can be reduced by lowering supply voltage and
  turning off accelerometer

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Applications of Accelerometers

• Automotive Airbag control units, anit-lock
  braking systems, and stability control systems
• Military and Aerospace inertial applications
  such as guidance, navigation, and targeting.
  These applications require precise and reliable
  measurements of acceleration.
• Home security alarms and motion detectors.
  Detects small changes in tilt angles or
  displacement

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Mass-Spring system

• Hookes law.
• F kx
• k is the constant
• x is the displacement
• F is the force
• Newtons second law of motion.
• F ma
• Resultant force equals ma
• Acceleration a will cause the mass to be
  displaced by

Image provided by http//ccrma.stanford.edu/CCRMA
/Courses/252/sensors/node9.html
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Mass spring system of the ADXL105

• It consists of a mass spring system as well as
  system to measure displacement.
• The mass is made of silicon, and has four
  fasteners in each corner of the mass.
• If acceleration occurs, than the mass will be
  displaced.
• Displacement of the mass is proportional to the
  acceleration.

Image provided by http//ccrma.stanford.edu/CCRMA
/Courses/252/sensors/node9.html
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Electrical Property of Capacitance

• Capacitors
• Electrical components that store charge
• Formed by placing two metal plates in parallel
• Dual Capacitor system used to measure
  displacement
• k is the property of material between the two
  plates
• Xo is the spacing between plates

Image provided by http//ccrma.stanford.edu/CCRMA
/Courses/252/sensors/node9.html
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Analysis of the Capacitor system

• At rest the capacitor contains capacitance of
• If the middle plate is moved by a distance x,
  then
• which can be expressed as
• The accelerometer also measure the difference
  between the two capacitors, which is given by

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ADXL105 Application Circuit

• Negative feedback ensures that the movement of
  the mass is kept small.
• Due to the minimal movement of the mass the
  capacitance equations remain true.

Image provided by http//www.alldatasheet.co.kr/
datasheet-pdf/view/AD/ADXL105.html
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Square Wave

• Fixed capacitor plates are driven by a 180 degree
  out of phase square wave.
• Acceleration causes the beam to deflect and it
  unbalances the differential capacitor.
• The result is an output square wave whose
  amplitude is proportional to acceleration.

Image provided by http//users.uma.maine.edu/facu
lty/rsm/slides/chap4/f4-3b.gif
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Characteristics ADXL105

• Analog Devices ADXL105 Accelerometer is a high
  accuracy MEMS (micro-electrical-mechanical
  system) accelerometer embedded on a small
  microchip.
• Measures the amount of acceleration felt in both
  positive and negative direction.
• Outputs 0 to 5 Volts with a maximum range of -5
  to 5 Gs.
• G acceleration due to gravity 9.8 m/s2.
• The voltage is proportional to acceleration

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Characteristic Polysilicon Structure

• Sensor is a surface micromachined polysilicon
  structure built on top of the silicon wafer.
• Provides resistance against acceleration induced
  forces.
• ADXL105 uses 2 um-thick polysilicon process.

Image provided by http//www.andrew.cmu.edu/user/
jamess3/MicrofabSeminar.pdf
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Characteristic Noise Density

• As the supply voltage is increased, the noise
  density dramatically decreases
• As the supply voltage is decreased, the
  accelerometers noise performance is degraded

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Characteristic Sensitivity Shift

• The sensors sensitivity changes by less than 2
  even at its maximum temperature threshhold
• The ideal operating condition can be seen to be
  approximately 30 degrees C.

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Brake Intensity Warning System

• Warns drivers of braking intensity of cars up
  ahead
• Will help to reduce rear end traffic collisions
• Will be implemented into existing GPS Navigation
  Systems

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A Need for Change

• Out of 1817 reported traffic accidents on the
  Orange County Orlando Expressway system in 2003,
  48 were rear end accidents
• The number of rear end traffic accidents
  increases each year
• Traditional brake lights are not effective

Image Provided By http//www.answers.com/main/ntq
uery?method4dsnameWikipediaImagesdekeyCar.ac
cident.arp.750pix.jpggwp8
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System Design

• ADXL 105 outputs analog signal to A-D converter
• Onboard navigation system monitors braking output
• Navigation system will send data and GPS
  coordinates via Bluetooth wireless connection
• Navigation system of rear car receives data and
  alerts driver via audio and/or video in the event
  of heavy braking
• (approximately 1.3 Gs)

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Competitive Products

• Traditional brake lights-- Not effective in
  preventing rear end collisions
• Blinking third brake light
• Supposed to get drivers attention quicker
• Currently offered on models by Mercedes and Kia
• Variable intensity brake light
• Still in research stages
• Light intensity increases as braking force
  increases
• No products offer any solutions for drivers that
  may be not focused on the road (i.e due to
  children, CD players, or cellular phones)

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Cost of System

• Cost of navigation system 2,000
• (Package cost for Infiniti G35)
• Required software upgrades (per system) 50
• Additional GPS hardware costs (per system)
  100
• (Bluetooth hardware, Interface Upgrades)
• ADXL 105 Accelerometer 7.75
• AD 7705 Analog-to-Digital Converter 4.85
• Total Upgrade Costs 162.70

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Profit Estimates

• Number of cars sold last year with GPS systems
  300,000
• Selling price of upgrade navigation system
  2325
• Profit due to upgrades
• 48,750,000

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Questions

• ???