Group 27-SenseWalk

1. Group 27-SenseWalk Mark Applegate (EE) Sara Belichki (CpE) Matthew Czarniak (CpE) Nicholas Heintze (EE)

2. Motivation & Project Goals • Improve the independence and quality of lifefor the visually impaired. • Optimize a tool commonly used by the visually impaired.

3. How to we do this? • Sonar:detect upcoming obstacles and vibrate a motor attached at the user’s wrist. • GPS: the SenseWalk will hold the user’s saved routes to guide them when needed. • Bluetooth:the user will be alerted of upcoming instructions as they go about a route.

4. Sense Walk System Design MCU GPS Sonar SD Card Digital Compass Bluetooth Power Supply

5. Microcontroller MCU GPS Sonar SD Card Digital Compass Bluetooth Power Supply

6. Microcontroller Requirements • The SenseWalk requires a microcontroller that contains • High flash memory-between 256 KB-512 KB • High frequency • ADC peripheral • Supports UART connection • Low power

7. Microcontroller Options MSP430F6659 ATmega2560

8. Microcontroller Final Selection

9. Sonar Design MCU GPS Sonar SD Card Digital Compass Bluetooth Power Supply

10. Sonar Specs and Requirements • Distance From 1 meter to 3 meters • Sonar operate at 40kHz • Not affected by noise • Microcontroller calculate distance • Vibrate a motor at different magnitudes proportional to distance

11. Ultrasonic Transducer Selection

12. Ultrasonic Drive Circuit Options • 555 Timer • Square wave is highly distorted by load. • Phase shift Oscillator • Square wave is distorted by load. • 40kHz Crystal- CMOS Inverter Oscillator • Minimum distortion

13. Ultrasonic Transmitter Circuit Hex Inverter

14. Ultrasonic Receiver Circuit Quad Op Amp

15. Sonar Testing

16. Bluetooth MCU Sonar Bluetooth GPS Digital Compass SD Card Power Supply

17. Bluetooth Requirements • Only needs to be able to cover a short distance (Class 1 BT modules have a range of ~100 m, Class 2 ~10 m). • Needs to have a good data rate to ensure no delay. • Use UART to connected to embedded system. • Low power consumption. • Must have appropriate Bluetooth protocol to send out audio messages to headset.

18. Bluetooth Comparison PAN1315 RN-42

19. Bluetooth Module Selection RN-42

20. Navigation Design MCU GPS Sonar SD Card Digital Compass Bluetooth Power Supply

21. GPS Module Selection

22. Digital Compass Selection

23. SD Card & Breakout Board • San Disk 4 GB • Petite FatFS • SD Library

24. Loading Waypoints on SD Card • Use route planner to create CSV / GPX • Upload CSV file with waypoints to SD

25. Software Class Diagram SenseWalk SDCard Compass Bluetooth Sonar GPS Init() getDirection() getCurrentCoordinates() getCurrentWaypoint() sendBluetooth() calculateSonar() determineRelativePos() determineCorrection() Sonar SDCard Bluetooth Compass GPS determineDistance() sendMotorCommand() ConnectHS() Transmit() OpenFile() CloseFile() ParseWaypoints() CurrentWaypoint() calibrateCompass() currentDirection() establishConnection() currentCoordinates()

26. Power Supply MCU GPS Sonar SD Card Digital Compass Bluetooth Power Supply

27. Power Supply Requirements

28. AC-DC Efficiency Requirements • Energy Star Requirements have become industry standard “AC-DC External Power Supply- An external AC-DC power supply is an EPS designed to convert line voltage ac input into lower voltage dc output.” [1] Output Power: 14.4W Minimum Efficiency Requirement: 73% [1] http://www.energystar.gov/ia/partners/prod_development/revisions/downloads/FinalSpecV2.pdf

29. Flyback Switching Converter • High Efficiency 80+ % capable. • Least costly of all isolated switching power supplies. • Full isolation capable. • Ideal for 0-200Watts. • Limited to 200Watts due to high peak switch currents. Magnetic & Capacitive Component Issues Controller & FET selection EMI design issues

30. Continuous Conduction Mode VS Discontinuous Conduction Mode CCM DCM DCM • Lower energy in transformer= smaller transformer • Less windings = lower I2R Losses • Higher ripple current = output capacitor ESR requirements • Higher transistor and diode peak current requirements CCM Lower ripple current Lower transistor and diode peak current requirements Right Half Plane Zero requires complicated control loop Higher energy in transformer = larger transformer

31. Transformer Design DCM • Primary Inductance: 1.078mH • Primary Peak Current: 0.75A • Max Input RMS Current: 0.32A • Max Output RMS Current: 2.08A • Turn Ratio: 8.94 • Primary & Secondary Wire Size • Core Material Selection • Gap Length, Total Winding Area

32. Transformer Design Equations DCM

33. Transformer Design Equations DCM

34. MOSFET Selection • Power MOSFET required - 600V and >2 Amps. • Experiment with MOSFETs to find best fit for efficiency. • Switching losses - Low parasitic capacitances and fast rise/fall times will combat switching losses. • Conduction losses - Low Rds(on) will combat conduction losses.

35. High Voltage MOSFET Selection

36. Flyback Converter Schematic

37. AC-DC Efficiency Vs. Load

38. Li-ion Switching Battery Charger • Three states: Preconditioning, Constant Current, Constant Voltage [2] Courtesy of Texas Instruments

39. Battery Charger Schematic

40. Li-ion Battery • Capacity: 2600 mAh • Working Voltage: 7.2V • Peak Voltage: 8.4V • Cut off voltage: 5.5 V • Max Charging Current: 2 Amp • Length: 2.8" • Width: 1.45" • Height: 0.8" • Weight: 3.5 Oz

41. Linear Vs Switching Regulators Linear • Low Cost • Low Design Complexity • Low Noise • Small size • Poor Efficiency <40% • High Heat Dissipation Switching • High Efficiency 80+% • Extended Battery Life • Higher Cost • Higher Design Complexity

42. Boost converter Schematic

43. Current Progress

44. Who does what?

45. Current Budget

46. Questions?