Wireless Portable Emergency Sensing Device

1. Wireless Portable Emergency Sensing Device Group 10 Steven Garrett, ParamVora, Collin Liu ECE 445 : Senior Design

2. Presentation Outline • Introduction • Device Features • Hardware Design • Pulse Oximeter • Accelerometer • Bluetooth • Battery Circuit • Nexus One® Interface • Ethics • Competitors • Future Recommendations • Credits • Resources

3. Introduction • Project Objective: • Create an Automated device to sense and report potential outdoor emergencies • Useful in the event that the user… • falls and cannot get up • becomes unconscious • Also provides a user requested measurement of blood oxygen saturation and heart rate

4. Features • Emergency Safety Monitoring Features: • Accelerometer • Used for fall and possible injury detection • Pulse Oximeter • Monitor heart rate and blood oxygen level once a possible emergency has occurred • Bluetooth • Wirelessly transmit signals from the device for optimum freedom of motion • Low Power Consumption • Travel long distances without burning through batteries • Cell Phone Interface and GPS Feature • Automatically call emergency medical services using an Android phone if needed • Using GPS, transmit location to EMS personnel

5. Hardware TPS61016 Boost Converter Power LED Drive Ckt Speaker Ckt Bluetooth Module MSP430 Microcontroller Accelerometer

6. Initial Circuit Testing • Bread-board Circuit Used to Test individual Hardware Components • Bluetooth Communication • LED-Drive Circuit Switching • Accelerometer Sampling • Pulse-Ox Signal Sampling • Speaker and Switch Operation

7. Hardware: Device PCB Layout 76.2256 x 22.3928 mm • Primary Device Circuit Layout

8. Hardware: Power PCB Layout 22.447 x 12.7 mm Power Supply Unit

9. Primary Circuit Accelerometer Power Supply Unit

10. Photodiode: First Stage Amp • The feedback resistor controls the gain • Optimal gain is the highest value possible in the range of the A/D converter Nonin Sensor Design Of Pulse Oximeters [1] Nellcor Sensor

11. Photodiode: Second Stage Amp • Subtracting Amplifier Circuit • Reduce DC offset and amplify signal • Gain is Adjustable using MSP430 internal resistor ladder • Chosen gain:

12. Pulse Oximeter: Digital Filter • Pulse Oximeter Sampling Rate: 310Hz • Desired Cutoff Frequency: 5Hz • Ensure that 60Hz and 120Hz signals are minimized • Gain: 10 x 104 Low Pass Filter Magnitude Response

13. Pulse Oximeter: Filtered Waveform • Filter Chosen as a balance between computational expense and signal clarity LED Voltage Switching

14. Pulse Oximeter: Final Waveform • Final Stage: estimate DC offset and subtract from the filtered signal • Digital DC estimation emulates a rectifying capacitor • Heart rate found using rising edge detection • SPO2 found empirically from signal ratios • Proportionality requires equal DC offset of • first stage amplifier for red and IR signals Infrared Signal Red Signal

15. Accelerometer • XYZ-Axis Sensing • Optimal Sensitivity: 600 mV/g • [2] • Energy Expenditure calculated in .8 second time window • Expenditure threshold found by empirical testing

16. Accelerometer High Pass Filter • Median Filtered Signals are High Pass Filtered to remove Tilt sensing information • Filter Order: 35 • Sample @ 45Hz • Cutoff @ .5Hz • Unity Gain High Pass Filter Frequency Response

17. Accelerometer Signals

18. Energy Expenditure Vibration Fall Detected • Fall is detected as Energy exceeds threshold of 19 • Heavy vibration does not exceed threshold

19. MSP430 Code Layout Diagram

20. Bluetooth • Class A Bluetooth device ~33ft range • Provides Wireless Link Between Phone and MSP430 • Acts as a Wireless RS-232 Port Using Serial Port Profile (SPP) • Useful for interfacing the device with a PC • Allows for real time data analysis in LabView

21. Android Application Components • User Interface file • Service file – consists of 2 threads depending on state • ConnectThread- runs during a pending connection • ConnectedThread- runs while connected • States to help facilitate debug and keep program stable • 1- No actvitiy (initializing state) • 2- Connecting to device • 3- Connected to device • Handler – interfaces the user interface with the background service • Java.io.IOStream

22. Android Application Flow Receive Flags 00FF00: Heart rate and Sp02 data to be followed 00FF01: End of data 00FF03: Emergency detected! FF5500: Reset flag Sent Flags 00FF02: user requests data 00FF04: confirmation of received emergency flag

23. Byte Handling and Error Checking • Fixes latency error by comparing the received buffer length and the stream buffer length • Repeats read() statement till they equal each other

24. Battery Circuit Test: • Output 3.44V with 520mV ripple Pk-Pk driving a LED • AA Battery Life > 3 hours under strenuous testing • Extended Battery Life >7 hours with Normal operation • Operable On Standard Battery Sizes

25. Helmet Technology: • Giro E2 Mountain Bike Helmet • Technology Safety Features • In-Mold Construction • Expanded Polystyrene (EPS) • Prolong and soften impact • Polycarbonate Shell • Helmet exoskeleton • Technology Safety Features • Placement between Polycarbonate shell and EPS • Extra ventilation system may be required [4] Helmet Internal Structure

26. Future Product Competitors: • CodeBlue: Wireless Sensor for Medical Care • Harvard Biosensor Group • Others fall detection system currently targets senior residents at nursing homes [5] Code Blue Developed by Harvard Sensor Group

27. Ethics: • Before manufacturing the device, system should be tested under multitude of conditions • Threshold for the emergency calling feature will be tested and set at a reasonable range to minimize false alarms and missed detection • System is designed to save endangered lives, not prevent injury

28. Future Recommendations: • Pulse Oximetry is not ideal for movement intensive applications • Inherently Noisy Signal • Ambient light causes inaccuracy • Placement “sweet spot” varies with individuals • Use microcontroller with integrated hardware multipliers for increased filter efficiency • Choose different accelerometer with a matching voltage range with microcontroller • Accelerometer outputs max 3.3V, but is clipped at the 2.5V—limitation of MSP430.

29. Special Thanks To: • Nonin® • Texas Instruments • Sunstone® Circuits • National Instruments Technical Support • ECE Electronic Part Shop • Mark Smart • Professor Carney • ChristynCollum

30. Resources: • [1] J.G. Webster, Design of Pulse Oximeters, New York: Taylor and Francis Group,   LLC, 1997. • [2] Human Fall Detection Using 3-Axis Accelerometer, Freescale Semiconductor Inc., Chandler, AZ, 2005 • [3] A Single-Chip Pulse oximeter Design Using the MSP430, Texas Instruments., Dallas, Texas 2000 • [4] Giro., CA. [Online]. Available: http://www.giro.com/en-us/products/cycling-helmets/ionos/ • [5] Harvard Sensor Lab., CodeBlue: Wireless Sensors for Medical Care [Online]. Available:http://fiji.eecs.harvard.edu/CodeBlue • [6] Bicycle Helmet Safety Institute., Helmet Foam. [Online] Available: http://www.helmets.org/research.htm

31. Thank You Questions?