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Wireless Portable Emergency Sensing Device
Group 10Steven Garrett, Param Vora, Collin Liu
ECE 445 : Senior Design
Presentation Outline1. Introduction2. Device Features3. Hardware Design
◦ Pulse Oximeter ◦ Accelerometer◦ Bluetooth◦ Battery Circuit
4. Nexus One® Interface
5. Ethics
6. Competitors7. Future
Recommendations8. Credits9. Resources
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
Introduction
◦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
Features
HardwareLED Drive Ckt
Accelerometer
Speaker Ckt
BluetoothModule
MSP430 Microcontroller
PowerTPS61016 Boost Converter
Initial Circuit TestingBread-board Circuit Used to Test individual Hardware Components
Bluetooth Communication
LED-Drive Circuit Switching
Accelerometer Sampling
Pulse-Ox Signal Sampling
Speaker and Switch Operation
Hardware: Device PCB Layout
76.2256 x 22.3928 mm
Primary Device Circuit Layout
Hardware: Power PCB Layout
22.447 x 12.7 mm
Power Supply Unit
Primary Circuit
Power Supply UnitAccelerometer
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
Nellcor Sensor
Design Of Pulse Oximeters [1]
Photodiode: Second Stage Amp
Offset
+
-
VCC
Vout
Vin
R2
R115 14out offset inV V V
• Subtracting Amplifier Circuit
• Reduce DC offset and amplify signal
• Gain is Adjustable using MSP430 internal resistor ladder
• Chosen gain:
Pulse Oximeter Sampling Rate: 310Hz
Desired Cutoff Frequency: 5Hz◦ Ensure that 60Hz
and 120Hz signals are minimized
Gain: 10 x 104
Pulse Oximeter: Digital Filter
Low Pass Filter Magnitude Response
Pulse Oximeter: Filtered Waveform
LED Voltage Switching
Filter Chosen as a balance between computational expense and signal clarity
Pulse Oximeter: Final Waveform
Infrared Signal Red Signal
• 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
2
( )
[ ( )]rms
prms
Log V redS O
Log V ir
XYZ-Axis Sensing Optimal Sensitivity: 600 mV/g [2] Energy Expenditure calculated in .8 second
time window Expenditure threshold found by empirical
testing
Accelerometer
Median Filtered Signals are High Pass Filtered to remove Tilt sensing information
Filter Order: 35 Sample @ 45Hz Cutoff @ .5Hz Unity Gain
Accelerometer High Pass Filter
High Pass Filter Frequency Response
Accelerometer Signals
Energy Expenditure
Vibration Fall Detected
Fall is detected as Energy exceeds threshold of 19Heavy vibration does not exceed threshold
MSP430 Code Layout Diagram
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
Bluetooth
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
Android Application Components
Android Application Flow
Receive Flags1. 00FF00: Heart rate
and Sp02 data to be followed
2. 00FF01: End of data3. 00FF03: Emergency
detected!4. FF5500: Reset flagSent Flags5. 00FF02: user
requests data6. 00FF04:
confirmation of received emergency flag
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
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 withNormal operation
Operable On Standard Battery Sizes
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
Helmet Technology:
[4] Helmet Internal Structure
CodeBlue: Wireless Sensor for Medical Care◦ Harvard Biosensor Group
Others fall detection system currently targets senior residents at nursing homes
Future Product Competitors:
[5] Code Blue Developed by Harvard Sensor Group
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
Ethics:
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.
Future Recommendations:
Nonin® Texas Instruments Sunstone® Circuits National Instruments Technical Support ECE Electronic Part Shop Mark Smart Professor Carney Christyn Collum
Special Thanks To:
[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
Resources:
Thank YouQuestions?