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?