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									Brake Intensity Advisory System




 ECE 4007 Senior Design Final Project Report

          Section L01, Brakes Team
       Project Advisor, Dr. Linda Milor

                 Jace Hall
               Michael Purvis
               Caleb Trotter
                  Ed Yri




                  Submitted

              December 14, 2011
                               Table of Contents

Executive Summary …………………………………………………………………………..ii

1. Introduction ………………………………….…………………………………….……..1

       1.1 Objective ………………………………………………….………………………...….1
       1.2 Motivation ……………….…………………………………………….………….…...2

2.     Project Description and Goals ………………………….………………………...….….2

3.     Technical Specifications ………………………………………….……………....….…..4

4.     Design Approach and Details ……………………….…………………...………...........4

       4.1 Force Sensor Input ....………………………………………………………………….5
       4.2 Processing Unit ………….…………………………………………………….………5
       4.3 Output ……………………………………………………………………....……..…..7
       4.4 Codes and Standards …………………………………………………………….….....8
       4.5 Constraints and Alternatives ………………………………………………………......9

5.     Schedule, Tasks, and Milestones ……………………………………………….………..9

6.     Results and Acceptance Testing………………………………………………………….10

7.     Budget and Cost Analysis ………………………………………………………………..11

8.     Conclusions and Future Work …………………………………………………………..13

       8.1 Conclusions …………………………………………………………….……………..13
       8.2 Future Work …………………………………………………………………………..14

9.     References ………………………………………………………………………...……....15

Appendix A ……………………………………………………………………………………A1

Appendix B ……………………………………………………………………………………B1




     BIAS Team (ECE 4007lm2)                                             i
                                        Executive Summary

The objective of the BIAS (Brake Intensity Advisory System) is to visually alert other drivers that “hard

braking” is occurring. The system consists of a brake pedal, a force sensor, a microcontroller, and a set of

LEDs located around the perimeter of a standard brake light. When the driver who is using the BIAS

presses the brake pedal, a force sensor and microcontroller determines if “hard braking” is occurring and

relays the appropriate signal to the brake light. The BIAS analyzes user-applied pedal force to illuminate

the LEDs. The motivations for the BIAS come from high volumes of rear-end collisions, which are the

second most frequent type of automobile accident. The prototype targets all car manufacturers concerned

with incorporating innovative safety features into future vehicle designs. The principle goals of the

design are increasing safety and providing drivers with a more detailed description of braking tendencies.

Although other forms of braking indication systems have been proposed, none use force-sensing resistor

(FSR) technology. The input to be processed by the control circuitry is provided via an FSR attached to

the brake pedal, and the output is relayed to a voltage divider circuit for conversion. The voltage divider

circuit converts the resistance value into a voltage between 0-3.3 V, which is interpreted by the processing

unit. The processing unit consists of a microcontroller and LED drivers to implement a real-time system.

The mbed platform was used to handle the system processing in order to reduce development time. The

LED drivers alert other vehicles of the force applied to the brakes by increasing the area of illumination

produced by the LED array. The array consists of three LED lines corresponding to three specific areas.

Non-intrusive design and simplistic integration with future braking systems will establish the prototype’s

marketability. With a parts cost of $128.97, low mass production cost is achievable.




  BIAS Team (ECE 4007lm2)                                                                                     ii
1.      Introduction

The Brake Intensity Advisory System (BIAS) is a method that visually indicates to other drivers when

“hard braking” occurs. The major components of the BIAS are a brake pedal, a force sensor, a

microcontroller, and a brake light composed of LEDs. The BIAS senior design team spent $128.97 to

develop the prototype.



1.1.    Objective

The objective of the BIAS is to visually alert drivers that “hard braking” is occurring in vehicles within

their line of sight. The system consists of a brake pedal, a force sensor, a microcontroller, and a set of

LEDs located around the perimeter of a standard brake light. When the driver who is using the BIAS

presses the brake pedal, a force sensor and microcontroller determine if “hard braking” is occurring and

relay the appropriate signal to the brake light. The BIAS analyzes user-applied pedal force to illuminate

the LEDs. Figure 1 shows a block diagram of the system.




Figure 1. Overview of the Brake Intensity Advisory System.

BIAS Team (ECE 4007lm2)                                                                                      1
1.2.      Motivation

The motivations for the BIAS comes from high volumes of rear-end collisions, which are the second most

frequent type of automobile accident. Although these types of accidents only make up 17% of all claims,

the average cost of each incident is over $13,000 [1]. This prototype is implemented in a Ford Motor

Company vehicle, but in the future, will target all car manufacturers concerned with incorporating

innovative safety features into future vehicle designs. By creating the BIAS, the senior design team hopes

to decrease the quantity of rear-end collisions while increasing the overall safety on the highways.



2.        Project Description and Goals

The BIAS analyzes user applied brake pedal force to control an auxiliary set of LEDs located around the

perimeter of standard brake lights. The system gives a visual indication of braking force, as seen in

Figure 2, by

        Illuminating an increasingly larger area of LEDs when “hard braking” force is applied, and

        Incorporating a delay between the standard brake lights and the auxiliary LEDs.




Figure 2. Actual visual progression of braking intensity using the BIAS prototype.




BIAS Team (ECE 4007lm2)                                                                                   2
Due to the simplistic design of the BIAS, all of the proposed design goals were met. These goals included

       Ease of integration with current braking systems

       Added hardware cost of less than $150

       Non-intrusive design

       Real-time response

       Manufacture software definability based on specific car model brake pressure parameters

However, in order to achieve all of the proposed goals, a few design modifications were necessary,

including

     A 12 volt regulator was added to the LED driver circuit in order to prevent any overvoltage
      supplied by the automobile’s power supply

     A 1.5MΩ grounding resistor was added to the LED driver circuit in order to drive the control pin
      to ground when floating

     The grounds on all of the circuits were unified in order to stabilize the system




BIAS Team (ECE 4007lm2)                                                                                 3
3.       Technical Specifications

Table 1. Technical specifications

Force Sensor
     Thickness                                                     Max. 0.208mm
     Force Range                                                      0-100 lb.
     Response Time                                                      5 μs
     Linearity Error                                                  <+/- 5%
     Voltage Range                                                   0 – 5 VDC
Microcontroller
     ADC                                                        Min. 8-bit, 400KHz
     PWM Output                                                Min. 3 channel output
     Clock Speed                                                    Min. 1MHz
     Memory                                                          Min. 64kB
LED
     Luminous Flux                                                     >0.5 lm
     Wavelength                                                     625-640 nm
     Operating Temp. Range                                      0°C – 80°C or better
LED Driver
     Operating Input Voltage                                         >12V DC
     Dimming Ability                                               PWM Control
     Max Driving Curent                                              ≥5000mA




4.       Design Approach and Details

There are three main focal points to the BIAS: the force sensor input, the processing unit, and the LED

array design. The force sensor detects braking intensity from a user. The processing unit monitors the

force sensor and controls the LED array. The LED array’s illumination area increases after passing an

intensity threshold. The “hard braking” threshold was determined to be 1.9V. The experiment consisted of

placing a force sensor on a vehicle and varying the applied brake pressure.


BIAS Team (ECE 4007lm2)                                                                                   4
4.1.    Force Sensor Input

The input to be processed by the control circuitry is provided via a force-sensing resistor (FSR). The FSR

outputs a resistance, which is proportional to the force applied by the driver. As the force increases, the

value of resistance decreases. The sensor is attached to the brake pedal and the output relayed to a

voltage divider circuit for conversion, as seen in Figure 3. The voltage divider circuit converts the

resistance value into a voltage between 0-3.3V that is interpreted by the processing unit.




Figure 3. Force-sensing resistor and voltage divider circuitry .



4.2.    Processing Unit

The processing unit consists of a microcontroller and LED drivers to implement a real-time system. The

mbed platform was used to handle the system processing in order to reduce development time. It provides

ADC support along with Pulse Width Modulation (PWM) outputs. PWM signals control the LED circuits

as shown in Figure 4.




BIAS Team (ECE 4007lm2)                                                                                       5
Figure 4. System diagram with detailed LED driver circuit.



An ADC is needed in order to capture data points from the force sensor. Interrupt-driven input data

acquisition drives the programmed state machine in Figure 5. In the interrupt routine, voltage levels from

the FSR circuit are categorized by the voltage threshold for “hard braking”.




BIAS Team (ECE 4007lm2)                                                                                  6
Figure 5. ADC interrupt driven state machine intended for mbed.



As shown in Figure 5, state changes caused by passing voltage thresholds change the PWM control

signals to the LED driver. The drivers control the on/off switching of the LED lines within the array and

also have the ability to change the luminosity of the LED lines. The code for the state machine can be

seen in Appendix A.



4.3.    Output

The LED array alerts drivers of the force applied to the brakes by increasing the illumination area. All

LEDs have a wavelength of 630nm +/- 5nm. The array consists of a minimum of three LED lines

corresponding to Areas 1, 2, and 3 in Figure 6. Area 1 functions as a normal brake light. Engaging the

brakes will illuminate Area 1, state “Light Braking” in the state machine. As the “hard braking” threshold

is crossed, states “Hard Braking 1” and “Hard Braking 2” in the state machine, Area 2 and Area 3, will




BIAS Team (ECE 4007lm2)                                                                                     7
illuminate with a slight delay in between. This delay creates a “step-through” animation that increases the

illumination area.




Figure 6. LED Array Configuration divided into Areas 1, 2, and 3.



4.4.    Codes and Standards

The BIAS does not currently employ any standard. A controller area network bus (standard ISO 11898-1)

will have to be considered for integration into a vehicle’s network [2]. Current LED based automotive

brake lights must conform to SAE J1889 standards [3].




BIAS Team (ECE 4007lm2)                                                                                   8
4.5       Constraints and Alternatives

Constraints

         LED array must run off of a 12V DC line

         System size must be small in order to be non-intrusive to operators

Alternatives

An alternative to the force sensor input was to retrieve data from the ABS of a vehicle. Modifying the

ABS within a vehicle was not viable due to safety and legal concerns. Alternative microcontrollers were

also considered, including TI‟s MSP430 and the PIC family. These were not chosen due to limited PWM

capabilities and additional development of I/O based circuit boards for the microcontrollers. The Atmel

MSL2040AU was another LED driver choice, but could not be used due to availability.



5.        Schedule, Tasks, and Milestones

Figure 7 displays a detailed schedule of tasks for the BIAS design, while Appendix B contains a Gantt

chart outlining these tasks.




Figure 7. Schedule of tasks and milestones.

BIAS Team (ECE 4007lm2)                                                                                   9
6.      Results and Acceptance Testing

The BIAS was demonstrated by attaching a force sensing resistor to a vehicle brake pedal while, the

circuitry and LED array was attached to a subsidiary platform. The brake pedal was pressed to replicate

normal braking force that was calculated to be less than 1.9V. When the pedal was pushed under these

conditions, the standard brake light illuminated, as seen in Figure 8. During the demonstration, the

voltage threshold of less than 1.9V was confirmed through use of a voltmeter.




Figure 8. Standard brake light illumination.



“Hard braking” was displayed by further increasing the force applied to the brake pedal. When the “hard

braking” threshold of greater than 1.9V was achieved, a second and third set of LEDs were illuminated

after a short, but visually perceivable delay of 0.25s as in Figure 9. All three areas of LEDs remained

illuminated until the driver no longer applied force to the brake pedal. The 0.25s delay was verified

through the use of a timer that is included in the mbed software.




BIAS Team (ECE 4007lm2)                                                                                   10
                                                   +0.25s




Figure 9. The step through illumination of “hard braking.”



7.        Budget and Cost Analysis

To help aid in the determiniation of the cost to develop BIAS, Table 2 gives a breakdown of the part

prices needed to develop the protoype for the BIAS. Table 3 shows a detailed description of the hardware

required and the cost of each.



Table 2. Cost of Development
     BIAS Component       Labor Hours     Wage/Hour      Labor Cost     Equipment Cost       Total Cost
 LED Array Assembly              42          $30.00         $1,260.00        $35.42           $1,295.42
 Install Force Sensor            4           $30.00          $120.00         $27.20            $147.20
         Program
                                 5           $30.00          $150.00         $59.00            $209.00
      Microcontroller
     Project Meetings            14          $30.00          $420.00          $0.00            $420.00
      Demonstration              3           $30.00          $90.00           $0.00            $90.00
          Totals                 68          $30.00         $2,040.00        $121.62          $2,161.62




BIAS Team (ECE 4007lm2)                                                                                  11
Table 3. Hardware costs breakdown


                                          Hardware Costs
         Component                               Model                   Unit Price     Quantity      Price
             LED                             516-1372-ND                    $0.77          46         $35.42
         LED Driver                         AP8803WTG-7                     $1.50           3         $4.50
Breakout Board (SO23 to DIP)                  BOB-00717                     $0.95           3         $2.85
        Force Sensor                 KIT-S-20-1000-FS100LB-KT              $27.20           1         $27.20
       Microcontroller                            mbed                     $59.00           1         $59.00
                                                                                            Total $128.97


Production Cost Projection

To date, there have been no similar BIAS products introduced into the market. Since a BIAS does not

already exist, this allows for complete control of the market. According to [4], there were approximately

12.1 million vehicles produced in 2010. Of those 12.1 million vehicles produced, 16.44% were produced

by the Ford Company [4]. The following development cost projections (Table 4) and profit projections

(Table 5) are based on 500,000 BIAS units being installed in Ford vehicles within the first year of

production with an estimated profit per vehicle of $2.00.



                       Table 4. Development Cost

                             Components of Development                  Cost

                         Hardware                                     $128.97

                         Labor                                        $2040.00

                         Overhead                                      $50.00

                                                            Total     $2,218.97




BIAS Team (ECE 4007lm2)                                                                                  12
                          Table 5. Projection of profit for the first year

                                                                      Quantity

                           Royalty per Vehicle                           $2.00

                           Number of Vehicles                          500,000

                                                 Total Profit       $1,000,000.00



Previously the team calculated the total cost of design to be $14,303.80. As can be seen in Table 4,
production cost has been greatly reduced to $2,218.87. The reasoning behind this large discrepancy in
cost is due to the fact that the previous values were based on the group producing the BIAS in mass
production for a year. The newly calculated price is based on the cost for one BIAS prototype to be
designed and built.


8.        Conclusions and Future Work

8.1       Conclusions

The BIAS prototype was fully operational, and all of the design goals and technical specifications were

met. Only a few modifications to the initial design were made. The BIAS was designed in a simple

manner so that the senior design team would have enough time to complete all of the design goals and

specifications before December 14, 2011. If improvements were to be made to the prototype, they would

include

         Using a printed circuit board with a more circular layout for the LED arrays

         Displaying the prototype in a more visually appealing manner rather than on a sheet of plywood

         Designing a more realistic brake light lens to accent each level of braking intensity




BIAS Team (ECE 4007lm2)                                                                                   13
8.2       Future Work

Steps to take to go from prototype to production

      1. Find replacement microcontroller that meets technical specifications at a much lower cost.

      2. Program new microcontroller with state-machine.

      3. Integrate system within a car manufacturers existing vehicle design.

      4. Fabricate circuit board to accommodate new microcontroller, existing circuitry, and manufacturer

          specifications.




BIAS Team (ECE 4007lm2)                                                                                14
                                           References

[1]    Occupational Health and Safety Administration, “Causes and Solutions of Fleet Safety
       Accidents,” Power Point, N/A. [Online]. Available:
       www.osha.gov/dcsp/alliances/presentations/motor_vehicle_safety.ppt. [Accessed: Sep. 15, 2011].


[2]    ISO Committee, “Road vehicles-Controller area network (CAN),” ISO/CD 11898-1, Oct., 1999.


[3]    SAE International, “L.E.D. Signal and Marking Lighting Devices,” SAE J1889, 01 Jul., 2005.


[4]    Ward’s Automotive Group, “U.S. Vehicle Sales Market Share by Company, 1961-2010,” Excel,
       2011. [Online]. Available: http://wardsauto.com/keydata/historical/UsaSa28summary/. [Accessed
       Sept. 11, 2011].




BIAS Team (ECE 4007lm2)                                                                             15
Appendix A – Code for the State Machine
#include "mbed.h"
#include "math.h"

PwmOut Center(p23); //Center array control
PwmOut Middle(p22);//middle ring control
PwmOut Out(p21);//outer ring control
AnalogIn ForceSensor(p20); //Input from force sensor
DigitalOut myled1(LED1); //state 1 light
DigitalOut myled2(LED2); //state 2 light
DigitalOut myled3(LED3); //state 3 light
Serial pc(USBTX,USBRX); //debug

float Force; //Input value
float Force1; // previous input value
float check; //abs(Force - Force1) in order to check for noise
int partpwr = 500; // 0.5 ms = 500 us * can play with value
int fullpwr = 1250; // 1.25 ms = 1250 us * can play with value
int midlock =0; //lock for mid
int outlock =0; //lock for out
int test =0;

Ticker adcTimer; //timer for adc

void adc() { //adc aquirement
   Force1 = Force;
   // NVIC_DisableIRQ(TIMER3_IRQn);
// critical section
   Force = ForceSensor; //Read input and place in variable
   // NVIC_EnableIRQ(TIMER3_IRQn);
}

int main() {
   Center.period(0.002); //set period to 2 milliseconds aka 500 hertz

  adcTimer.attach_us(&adc,12000); //Sampling Freq = 20 times Input Freq. (20*4.167 Hz)
  while (1) {
    wait(0.02);

     // pc.printf( "Force = %f\r\n", Force);
     check = fabs(Force - Force1);

     if (check < 0.1) {
        NVIC_DisableIRQ(TIMER3_IRQn);
        if (Force < 0.109) { ///float value btwn 0.0 and 1.0 corresponding to 0V to 3V( 0.15V ~= 5%)
           NVIC_EnableIRQ(TIMER3_IRQn);
           //Off state - Everything to zero
           Center = 0;
           Middle = 0;
           Out = 0;
           myled1 =0;
           myled2 =0;
           myled3 =0;
           midlock =0;


BIAS Team (ECE 4007lm2)                                                                                A1
             outlock =0;
          } else NVIC_EnableIRQ(TIMER3_IRQn);
          NVIC_DisableIRQ(TIMER3_IRQn);
          if (Force >= 0.11 && Force < 0.54) { //1.29V = 43% EDIT: Changed to 0.54 for 1.9V threshold
             NVIC_EnableIRQ(TIMER3_IRQn);
             if (!midlock) { //lock for second state
                Center.pulsewidth_us(partpwr);
                Middle = 0; //shutoff middle
                Out = 0; //shutoff out
                myled1 =1; //indicator
                midlock =1; //engage middle lock
                outlock=0; //unlock outer
             }
          } else NVIC_EnableIRQ(TIMER3_IRQn);
          NVIC_DisableIRQ(TIMER3_IRQn);
          if (Force > 0.391) { // if greater than threshold voltage
             NVIC_EnableIRQ(TIMER3_IRQn);
             if (!outlock) { //Lock for third state
                myled2 =1;
                Center.pulsewidth_us(partpwr); //Center @ 1/2 pwr
                Middle.pulsewidth_us(fullpwr);// Middle @ full pwr
                wait(0.25); // Delay before Out -- starts "fourth state"
                myled3 =1;
                Out.pulsewidth_us(fullpwr);
                Center.pulsewidth_us(fullpwr);
                outlock =1; //engage outer lock
                midlock = 1; //keep middle lock
                // Purpose of keeping middle lock is so
                //brake light is not reset until no pressure isapplied
             }

           } else NVIC_EnableIRQ(TIMER3_IRQn);
        }//else { pc.printf( "check = %f\r\n", check); }

    }
}




BIAS Team (ECE 4007lm2)                                                                                 A2
Appendix B – Project Gantt Chart




BIAS Team (ECE 4007lm2)            B1

								
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