Brake Intensity Advisory System Design Assessment Jace Hall Michael Purvis Caleb Trotter Edward Yri ECE 4007-L01 11/02/2011
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.
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.
Design Goals - Simple integration with current braking systems - Non-intrusive design - Real-time response - Software definability based on vehicle brake force parameters
Technical Objectives • 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.
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.)
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.
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
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.
Problems Encountered with FSR Loose connections creating transients. Determining the proper fixed resistance value.
Why Mbed? • Extensive libraries for rapid prototyping • Meets technical requirements of proposal • Integrated 6 PWM channels
Program Overview State: Normal No braking force detected. State: Hard Braking 2 PWM1 = 80% Dc. PWM3 = 80% Dc. LED Arrays 1,2 & 3 on. Braking > 0 Yes Yes Braking= 0 State: Light Braking PWM1 = 40% Dc. LED Array 1 is on. Delay 0.025 s. State: Hard Braking 1 PWM2 = 80% Dc. LED Arrays 1 & 2 on. Braking > 1.9V Yes
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
LED Array Design Vin 12V Z1 LED Driver C1 Vin R1 GND SET SW L1 CTL PWM Signal
Brake Light Operation • Voltage threshold < 1.9 V. 1
2 Voltage threshold ≥ 1.9 V. 1 Brake Light Operation
Brake Light Operation • Voltage threshold ≥ 1.9 V after a 25 ms delay. 3 2 1
Budget/Cost Analysis • Prototype Budget Status • Of the requested $405, $98.99has 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.