1. Tire Tread Checking System Final Presentation Group #11 Rene Lamb, Byungchan Ryu, Jongho You

2. Overview Laser Rangefinder to MEASURE DISTANCE Rail System allows measurement across tire surface Microcontroller calculates tread depth RTC, accelerometer controls when the measurement takes place

3. Top Level System Block Diagram

4. Laser Rangefinder Parallax Laser Rangefinder 1 mm accuracy @ 15-20cm range Small spot size allows measurement into tread Specs Include: Power Requirements: 5 VDC @ 150 mA Communication: Asynchronous serial 300–115,200 baud with automatic baud rate detection Range finding sample rate of 1 Hz

5. Laser sensor measurement testing Measuring distance into the inner, outer surfaces of the tire 2 Tests, done from different locations

6. Laser Rangefinder Requirements/Verification RequirementsVerifications Sensor measures distance to an object 20 cm away with a resolution of 1 mm 1.Position the laser distance sensor 20 cm away from object. 2.Connect the sensor to the PIC microcontroller. 3.Make the laser output measurements continuously. 4.Move the laser towards the object by 1mm. Observe the measurement output. Sensor reports tread depth to ±1mm. 1.Place the sensor such that laser is pointing into the inner and outer surfaces of the tire (LT245/75R16) 2.Make measurements by interfacing with PIC microcontroller. 3.Compute tread depth by calculating the difference.

7. Real Time Clock SPI-bus Real Time Clock Relatively low current draw (~160 µA) Operating voltage of 2 ~ 5.5 V More accurate PIC’s Watchdog timer Triggers weekly alarm

8. RTC Requirements/Verification RequirementsVerifications RTC generates an interrupt signal after a preset amount of time in ± 10% accuracy 1.Connect RTC to PIC 2.Configure RTC to generate an interrupt every second 3.Program PIC to toggle an LED every interrupt 4.Time the LED toggles 5.Configure RTC to generate an interrupt every minute 6.Time the LED toggles

9. Power Supply Original Power Supply: Two series 1.5 V AA Batteries 3000 mAh RTC/PIC/Boost Converter 3.3 V Boost Converter WiFi/Accelerometer 5 V Boost Converter Laser Rangefinder/Servos Power Supply Modification 5 V Linear Regulator for RTC/PIC 16F877a PIC requires at least 4.5 V supply Did not have access to low voltage PIC version Supplied through 5 V linear regulator

10. Battery Life Calculation Power Source -2 Series 1.5 V batteries -3000 mAh total -PIC: 20 Mhz at 5.0 V Modes of Operation Current Draw -Sleep mode = 2.2 mA -Active Mode = 1036.3 mA Operation Periods (per week) -1 week = 604800 s -Sleep mode time = 604740 s -Active mode time = 60 s

11. Battery Life Calculation

12. 5V/3.3V Boost Converters 2MHz Switching Regulators Up to 2.1 A Output Current Accepts Vin between 2.3 and 5.5 V Adjustable Vout via external voltage divider PIC controlled Enable pin allows for power savings Enable PIN Low causes true load disconnect, cutting current flow to devices

13. 5.3/3.3 V Boost Converters Calculations Programming Vout Vout = 1+R1/R2 Allowed Inductor Ripple diL =.3 * Iout(max) * Vout/Vin Minimum Inductor Value L = Vin * (Vout – Vin) / (diL * fsw * Vout) Component/Value3.3 V Regulator5 V Regulator R1 (k Ω )230N/A R2 (k Ω )100N/A I out(max) (A)1.8 V in (V)3.0 V out (V)3.35.0 f sw (MHz)2.0 di L (A).59.9 L (uH).23.6

14. Duty Cycle D = 1 – (Vin * n / Vout) n ≈.9 Minimum Capacitance at Output Cout(min) = (Iout(max) * D) / (fsw * dVout) Minimum Capacitance at Input Data Sheet Recommended 22uF 5.3/3.3 V Boost Converters Calculations Component/Value3.3 V Regulator5 V Regulator I out(max) (A)1.8 V in (V)3.0 V out (V)3.35.0 f sw (MHz)2.0 C out (uF)1.62.76 D.18.46

15. Boost Converter Requirements/Verification RequirementsVerifications 5V Converter provides constant output voltage within the range of 4.85V < 5V < 5.15, with and without current draw. 1.Supply power supply breakout PCB with 3 V. 2.Set EN pin high 3.Observe that output voltage is within range 4.Set EN pin low 5.Observe that output voltage is 0 V 6.Set EN pin High 7.Sweep DC voltage between 2.8 and 4.5 V 8.Observe that output voltage is within range 3.3V converter provides output voltage range of 3.0V<3.3V<3.6V, with and without current draw. 1.Supply power supply breakout PCB with 3 V. 2.Set EN pin high 3.Observe that output voltage is within range 4.Set EN pin low 5.Observe that output voltage is 0 V 6.Set EN pin High 7.Sweep DC voltage between 2.8 and 3.2 V 8.Observe that output voltage is within range

16. Accelerometer Vehicle Engine Causes Vibration when vehicle engine is on Sampled data from accelerometer used to determine if vehicle is on 16 bit two’s complement digital output data High resolution (4mg/LSB) Fluctuations occur in Z-axis acceleration when vehicle is on

17. Accelerometer: Vehicle Testing Results Goal: Verify that accelerometer can be used to determine if vehicle is moving Accelerometer mounted to hood of vehicle (2006 Mitsubishi Eclipse) Sampled accelerations when vehicle engine is off/on Calculated standard deviations of samples Set threshold for vehicle turn on based upon difference in standard deviations

18. Accelerometer: Vehicle Testing Results Average: 8.37 Standard Deviation:.065

19. Accelerometer: Vehicle Testing Results Average: 8.35 Standard Deviation:.152

20. Accelerometer: Lab Testing Vibrations in Lab modeled using phone application 20 Samples recorded from accelerometer Average and Standard deviation calculated by PIC Results displayed to LCD

21. Accelerometer Requirements/Verification ItemRequirementsVerifications Accelerometer Standard deviation of Z-axis acceleration samples produce STD = 0.00 when no vibration detected and STD >= 0.01 when vibration detected 1.Break out accelerometer on breadboard with test LCD Display to output collected data. 2.Perform 20 samples of Z-axis data. 3.Display standard deviation of sample on LCD and verify that STD = 0.00 4.Repeat step 2 with accelerometer breadboard resting above cellphone made to vibrate with vibration app 5.Display standard deviation of sample on LCD and verify that STD >= 0.01

22. Servo Motors Parallax Continuous Rotation Servo (Rail) - Ability to control Laser sensor along the slide - 1300µs(clockwise) - 1500µs (pause) - 1700µs(counter-clockwise) Arduino 180° Micro Servo (Shutter) - Extended servo arms - Shutter needs to slide about 6cm to open.

23. Servo Requirements/Verification RequirementsVerifications Servo (Rail) Servo moves counter-clockwise, clockwise, moves the rail in 5mm ± 0.1mm units. Connect the servo motor to the PIC, connect the servo to the rail system. Move the rail clockwise for 5 mm and measure distance moved. Repeat 5 times. Repeat for counter-clockwise direction. Servo (Shutter)Servo moves from 0 to 180 degrees Connect the servo motor to the PIC, send signal to the Digital I/O pin which servo is connected to, and observe 180 degrees movement.

24. Building the Test Setup

25. Spring Calculation Subtracted 10% of torque of servo motor ; - Accounting for the friction within the rail

26. Spring Calculation Torque of Servo for Rail is: 38oz/inch (2.375 lbs/inch) - The laser sensor will be able to slide about 10inchs long Torque of Servo for Shutter is: 1kg/cm (5.5997 lbs/inch) - the shutter block only need to slide about maximum length of 2 inches. Decide to use spring with spring rate of 0.10(lbs/inch)

27. Microcontroller Operation

28. Code Structure

29. Prototyped Board

30. System Functional Testing Location 1 Location 2Location 3 Location 4

31. Failed Verifications ItemRequirementsVerifications Boost Converters 3.3V converter provides output voltage range of 3.0V<3.3V<3.6V, with and without current draw. 1.Supply power supply breakout PCB with 3 V. 2.Set EN pin high 3.Observe that output voltage is within range 4.Set EN pin low 5.Observe that output voltage is 0 V 6.Set EN pin High 7.Sweep DC voltage between 2.8 and 3.2 V 8.Observe that output voltage is within range Android Phone Receive strings from the Wi-Fi module of the PIC Use the Phone to connect to the ad-hoc network created by the Wi-Fi module on the pic. Send and receive text data. Wi-Fi Module Use Wi-Fi interface to send and receive Serial Data Connect Wi-Fi module to the PIC board, set up an ad-hoc connection. Use telnet from a laptop, send and receive commands

32. Shortcomings No PCB incorporation - bad circuit design and scheduling - modular design process Test setup - Laser Rangefinder orientation - Height of Laser Rangefinder location

33. Future Works Sweeping algorithm detects where the treads are – no need for manual input Need to interrupt the measurement cycle if vehicle starts moving during measurement More accurate rail system A better solution to detecting the car’s status - interfacing with OBD2 system, CO 2 sensor, temperature sensor, etc Need for a better, cheaper sensor - temperature rating: 0 – 50 °C - better accuracy & shorter minimum measuring distance