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.

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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

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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