Brake Intensity Advisory System Design Assessment Jace Hall Michael Purvis Caleb Trotter Edward Yri ECE 4007-L01 11/02/2011

2 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 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.

4 BIAS

5 - Simple integration with current braking systems - Non-intrusive design - Real-time response - Software definability based on vehicle brake force parameters Design Goals

6 -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

7 High Level BIAS Schematic

8 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.)

9 Interpreting 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.

10 Determining 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

11 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.

12 Problems Encountered with FSR -Loose connections creating transients. -Determining the proper fixed resistance value.

13 High Level BIAS Schematic - Microcontroller

14 Mbed I/O

15 Why Mbed? Extensive libraries for rapid prototyping Meets technical requirements of proposal Integrated 6 PWM channels

16 Program Overview State: Normal No braking force detected. State: Normal No braking force detected. Braking > 1.9V Braking > 0 State: Light Braking PWM1 = 40% Dc. LED Array 1 is on. State: Light Braking PWM1 = 40% Dc. LED Array 1 is on. Braking = 0 State: Hard Braking 1 PWM2 = 80% Dc. LED Arrays 1 & 2 on. State: Hard Braking 1 PWM2 = 80% Dc. LED Arrays 1 & 2 on. State: Hard Braking 2 PWM1 = 80% Dc. PWM3 = 80% Dc. LED Arrays 1,2 & 3 on. State: Hard Braking 2 PWM1 = 80% Dc. PWM3 = 80% Dc. LED Arrays 1,2 & 3 on. Delay s. Delay s. Yes

17 High Level BIAS Schematic – LED Array

18 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

19 LED Array Design L1 R1 V in 12V C1 Z1 LED Driver LED Driver PWM Signal CTL GND V in SET SW

20 Current Limiting Resistors in LED Array

21 Brake Light Configuration

22 Brake Light Operation 1 Voltage threshold < 1.9 V.

23 Brake Light Operation Voltage threshold ≥ 1.9 V. 1 2

24 Brake Light Operation Voltage threshold ≥ 1.9 V after a 25 ms delay.

25 Budget/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.

26 Production Cost Break Down PartsMass Production CostPrototype Cost FSR$16.00$7.95 Wire/Connectors$5.50Donated Resistors/Voltage Regulator/Capacitors $4.95Donated Perforated Boards$5.75Donated Microcontroller $10.00Donated LEDs$19.25 LED Drivers$4.50 Parts Total$65.95$31.70 Contingency (15%)$9.89$4.76 TOTAL$75.84$36.46

27 Future Work TaskDeadline Assemble LED Array11/4 Program microcontroller11/16 Solder LED array circuit to perforated board11/19 Test LED array and microcontroller11/21 Integrate LED array, microcontroller, and FSR11/28 Finalize prototype12/2