brake intensity advisory system design assessment jace hall michael purvis caleb trotter edward yri...
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Brake Intensity Advisory System Design
Assessment
Brake Intensity Advisory System Design
AssessmentJace Hall
Michael Purvis
Caleb Trotter
Edward Yri
ECE 4007-L0111/02/2011
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Project Details Project Details
• What- BIAS (Brake Intensity Advisory System) operates by
illuminating an auxiliary set of LEDS located around the perimeter of the standard brake lights when “hard braking” occurs.
• Cost- The cost associated with mass production of the BIAS
is projected to be $75.84.
3
Project MotivationProject Motivation
• Why- The percentage of rear-end collisions (17% of all
claims) ranks second among all automobile accidents.
• Who- BIAS is intended for drivers and car manufacturers
who are concerned with operating and manufacturing safer vehicles.
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BIASBIAS
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- Simple integration with current braking systems
- Non-intrusive design
- Real-time response
- Software definability based on vehicle brake force
parameters
Design Goals
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- Receive a voltage sensor output between 0-3.3V corresponding to a defined force.
- Categorize the inputs into three defined states using the Mbed microcontroller.
- Illuminate the auxiliary LEDS when a voltage of 1.9V or higher is received by the microcontroller.
- Achieve a visual indication of braking force in real time.
Technical Objectives
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High Level BIAS Schematic High Level BIAS Schematic
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Force Sensing Resistor (FSR) Operation Force Sensing Resistor (FSR) Operation
- The FSR is a polymer thick film device.
- The output resistance decreases as the force applied increases.
- FSRs provide a cost benefit of two orders of magnitude over load cells (another commonly used force sensor.)
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Interpreting FSR Output as VoltageInterpreting FSR Output as Voltage
- The FSR must be connected to a voltage divider circuit to interpret the applied force as a voltage.
- A voltage regulator must be inserted to convert the input voltage to 3.3V due to Mbed voltage input constraints.
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Determining the Fixed Resistor ValueDetermining the Fixed Resistor Value
- The fixed resistor value in the voltage divider helps determine the sensitivity of the output.
- Decreasing RF allows for a more dynamic range of force values to be converted to a corresponding voltage.
- Test: Dynamic Braking Resistor Value: 63Ω-2000Ω
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Confirming the Theoretical Threshold Confirming the Theoretical Threshold
- The FSR was attached to a brake pedal and braking pattern voltages were recorded.
- The “hard braking” threshold was determined to be any voltage above 1.9V.
- A custom bracket was fabricated to ensure the applied braking force was absorbed solely by the FSR.
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Problems Encountered with FSRProblems Encountered with FSR
- Loose connections creating transients.
- Determining the proper fixed resistance value.
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High Level BIAS Schematic - MicrocontrollerHigh Level BIAS Schematic - Microcontroller
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Mbed I/OMbed I/O
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Why Mbed?Why Mbed?
• Extensive libraries for rapid prototyping
• Meets technical requirements of proposal
• Integrated 6 PWM channels
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Program OverviewProgram OverviewState: NormalNo braking force detected.
Braking > 1.9V
Braking > 0
State:Light BrakingPWM1 = 40% Dc.LED Array 1 is on.
Braking= 0
State: Hard Braking 1PWM2 = 80% Dc.LED Arrays 1 & 2 on.
State: Hard Braking 2PWM1 = 80% Dc.PWM3 = 80% Dc.LED Arrays 1,2 & 3 on.
Delay0.025 s.
Yes
YesYes
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High Level BIAS Schematic – LED ArrayHigh Level BIAS Schematic – LED Array
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LED Array and Driver Specifications LED Array and Driver Specifications
• LEDs - Outdoor and automotive rated
- Max luminous intensity: 5500 mcd- Max junction temp: 130°C
• LED Drivers- PWM control for dimmable LED output
- Max current : 1 A
- Max input voltage: 30 V
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LED Array DesignLED Array Design
L1
R1
Vin 12V
C1
Z1
LEDDriver
PWM Signal
CTL
GND
Vin
SET
SW
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Current Limiting Resistors in LED Array Current Limiting Resistors in LED Array
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Brake Light ConfigurationBrake Light Configuration
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Brake Light OperationBrake Light Operation
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• Voltage threshold < 1.9 V.
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Brake Light OperationBrake Light Operation
• Voltage threshold ≥ 1.9 V.
1
2
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Brake Light OperationBrake Light Operation
3
1
2
• Voltage threshold ≥ 1.9 V after a 25 ms delay.
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Budget/Cost AnalysisBudget/Cost Analysis
• Prototype Budget Status - Of the requested $405, $98.99 has been spent. All parts
have been procured at this time.
• Projected Implementation Cost- The BIAS prototype includes a more expensive
microcontroller and added voltage source. The cost of the production model will reflect these deducted costs.
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Production Cost Break DownProduction Cost Break Down
Parts Mass Production Cost Prototype Cost
FSR $16.00 $7.95
Wire/Connectors $5.50 Donated
Resistors/Voltage Regulator/Capacitors
$4.95 Donated
Perforated Boards $5.75 Donated
Microcontroller$10.00 Donated
LEDs $19.25 $19.25
LED Drivers $4.50 $4.50
Parts Total $65.95 $31.70
Contingency (15%) $9.89 $4.76
TOTAL $75.84 $36.46
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Future WorkFuture Work
Task Deadline
Assemble LED Array 11/4
Program microcontroller 11/16
Solder LED array circuit to perforated board 11/19
Test LED array and microcontroller 11/21
Integrate LED array, microcontroller, and FSR 11/28
Finalize prototype 12/2
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