Preliminary Design Review

Seizure Monitor Senior Design Project P06210Alexey Chernyakov (EE), Piyanant Siridej (EE)Eric Smith (ME), Zac Levine (ME),

Agenda

Description of the Process Request Requirement Specification Design

Description of the Design Drawing Block Diagram Circuit Schematics Flow Chart Bill of Materials

Description of the Implementation Plan Implementation Testing Evaluation

Process - Request

The initial written customer request-The parent would like a device that could detect the rhythmic motion their child exhibits during a seizure and set off an audible alarm to alert the night nurse or wake the parents themselves.

During the meeting with the customer, the situation was further clarified- Exhibits generalized tonic-clonic (GTC) seizures Seizure detection needs to occur in less than three minutes

After researching GTC seizures, two candidate seizure symptoms were identified- Abnormal motion, detectable by an accelerometer Increased heart rate, detectable by a heart rate monitor

Dr. Berg, the director of the Strong Epilepsy Center, gave further design considerations- A motion based system could be used to detect multiple types of seizures To detect multiple types of seizures, multiple detection units are needed A library of seizure data could be formed, leading to a robust detection algorithm

Process – Request (Continued)As our project involves not only our customers child, but also patients at

Strong Memorial Hospital, further documentation is required- A patient consent form to explain the risks and benefits Health Insurance Portability and Accountability Act (HIPAA)

certification to insure patient confidentiality and safety A testing protocol for University of Rochester’s and RIT’s internal

review boards (IRB)s

Since a robust multi-unit, multi-seizure type detection unit is beyond the scope and time constraints of our original design project, the project was divided into several development phases-

I. Develop an accelerometer based worn unit that can wirelessly transmit seizure data. The data will be sent and stored in the base unit.

II. Acquire a library of seizure data. Then use this library to develop a seizure detection algorithm for each seizure type.

III. Develop a base unit that can implement the seizure detection algorithms and alert a guardian in case of seizure activity.

Process - Requirements1. Seizure monitoring system during sleep time.

2. Continuous Battery operation up to 12-14 hours with exchangeable battery.

3. Monitoring system consists of 2 units; base unit and a worn unit.

4. Two units must communicate wirelessly over a distance of 150 feet.

5. No way of harming the wearer.

6. The worn unit will be easily attached/detached by a guardian.

7. The base unit will be capable to store at least 10 seizure events.

8. The base unit will alert the guardian of the seizure activity using an audible alarm on the base unit.

9. Develop a preliminary seizure detection algorithm to process the seizure data.

10. Using the collected seizure data validate the accuracy of the preliminary seizure detection algorithm.

Process - Specifications There may be up to 6 worn units communicating to the base unit to properly monitor

seizure activity.

A seizure activity will be detected using a 3-axial accelerometer with acceleration values up to 6g.

An accelerometer reading will be passed to the microcontroller on the worn unit where it will be checked against an adjustable threshold voltage.

ZigBee wireless communication will be used between the worn unit(s) and the base unit.

The transfer rate of data between two units will be 250 kbps.

The base unit will be capable of writing the seizure data to a USB flash drive with maximum capacity of 1GB in a text file format for later analysis.

The base unit will run on a standard wall outlet

The worn unit will run on 2 standard AAA batteries

Attach/Detach system, for the worn unit, will use a Velcro strap.

Size of the worn unit will be approximately 2.5” x 2.5” x 1.5”

Process – Specifications (Continued) 15 Hz max signal (tested) will be sampled at 120 Hz, converted through a

10 bit ADC

3 axis accelerometer, possibly 6 total accelerometers. Therefore 17280 bits/s

Typical max seizure length = 5 minutes. Therefore 5,184,000 bits < 1 Megabyte

Necessary transfer rate from worn to base: 2,880 bits/s (0.3515625 kb/s)

With 6 accelerometers the base unit must handle a transfer rate of 2.11 kb/s

Acceleration Info: +/- 6 g’s (tested) Bandwidth maximum = 150 Hz

Frequency Resolution is based on sample time, our 5 minutes could produce accuracy up to 0.003 Hz.

Specifications – Self Test

The battery voltage on the worn unit will be constantly monitored when the unit is turned ON. In the event it drops below 2.4V, the “Low Battery LED” on the worn unit will be turned ON.

The worn unit will implement a self test each time the unit is turned ON. This self test is used to test the following components and functions of the seizure monitor system:

Accelerometer (worn unit) Wireless transmitter (worn unit) Wireless receiver (base unit)

To ensure system integrity, the wireless communication system and accelerometer will be tested in addition to the startup test. The “System Operates Properly LED” on the worn unit will be blinking every second unless it is turned OFF during the self test as following:

Specifications – Self Test (Continued)

Wireless Communication Test In the event that no signal is transmitted from the worn unit to the base unit during one minute, a test signal will be sent to the base unit. The base unit will detect the test signal and will send it back to the worn unit. In the event that no signal is received back from the base unit, the “System Operates Properly” LED on the worn unit will be turned OFF.

In the event that no signal is received by the base unit from the worn unit (including the test signal mentioned above) during one minute, the base unit will trigger the sound alarm to alert the guardian. The “Communication Operates Properly” LED on the base unit will be turned OFF.

Specifications – Self Test (Continued) Accelerometer Test When the worn unit is turned ON, a small, unbalanced DC motor,

similar to those used in pagers and cell phones, will be activated for a second. The vibration produced by the DC motor will be detected by the accelerometer and the signal will be transmitted to the base station and written to a file.

In the event no signal is transmitted from the accelerometer to the microcontroller in one minute, the unbalanced motor will be turned ON by the microcontroller to “shake” the board. If no signal will be detected from the accelerometer, the “System Operates Properly” LED on the worn unit will be turned OFF and the “System Failure” signal will be sent to the base unit to produce an audible alarm to alert the guardian. A “System Failure” LED on the base unit will be turned ON.

Process – Design Decision Matrix for assessing top 3 candidates for GTC seizure monitoring

Scale (1-10 with 10 being the best)

FrequentlyExhibited

Easily Measured/ Ease of Use

Magnitude of Variation from

Baseline

Symptom Occurs

QuicklyCost Sum

Body Shakes 10 8 9 7 5 39

Breathing 7 4 6 4 5 26

Oxygen Saturationlevel

6 9 8 4 3 30

Blood pressure 7 6 7 7 6 33

EEG abnormality 10 3 10 10 2 35

Body Temperature 3 9 4 2 9 27

Heart rate 9 8 8 7 9 41

Process – Design (Continued)

Easy to implement using a base and a

worn unit?

Easy to attach/detach?

Accuracy of result?Continuous power for 14

hour operation?

Body shakes OK Best OK OK

EEG abnormalitydetected by multiple

electrode EEG recording

Worst Worst Best Worst

Heart rate Best OK Worst Best

Top 3 candidates for GTC Seizure Monitoring

Process – Design (Continued)

802.11 Bluetooth ZigBee UWB

Range ~ 100 m ~ 10 m ~ 100 m ~ 10 m

Throughput < 54 Mbps < 3 Mbps < 0.25 Mbps < 500 Mbps

Battery Life Fair Good Very good Good

Cost Fair Good Good Good

Ease of use Very good Fair Very good Good

Network Technologies Table

System Design Based on the Original Request

Person Exhibits

symptoms of Seizure

Device Detects

Symptom

Person has

seizure

Send Data Wirelessly

to Base Unit

Worn Unit

Base Unit

Receive Data from Worn Unit

Alarm Sounds

System Design Based on Requirements

Place Worn Unit on Patient

Turn On Device / LED ON turns on

Battery Low? No

Turn off the device and take Worn

Unit offReplace Battery

Turn On Base UnitReceive Data

from Worn Unit(s)

Device Ready and standby for

communicationYes

Alarms the guardian

Microcontroller reads data

No

Base Unit

Unit Ready Movement? Seizure?

No

Transceiver sends data to Base Unit

YesAnalyze data by

comparing to library

Worn Unit

System Design Based on the Specifications

Place Worn Unit on Patient

Pass?Initial Test on Worn Unit and

Network

Turn On Device / LED ON turns on

Pass LED turns on

Battery Low? No

Yes

No

Fail LED turns onTake Worn Unit off

Turn off the device and take Worn

Unit offReplace Battery

Movement?

Contact distributor

Yes

Amplitude/Frequency

above threshold?

Seizure Activity

Yes

Unit Ready

Perform self-test at t = initial time + 60

seconds.

no

Yes Pass?

Fail LED turns on. (alert?)

Transceiver sends data to Base Unit

Seizure Stops?

Yes

No

Worn Unit

Turn On Base UnitReceive Data

from Worn Unit(s)

Device Ready and standby for

Communication

Check Network Integrity

Yes

Pass?Yes

Writes data to flash Memory

Alarm the guardian

Microcontroller read/analyze data

No

No

Base Unit

Turn Off Base Unit

No

Design – Block Diagram of Overall Process

Design – Block Diagram of Worn Unit

Design – Circuit Schematics

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Preliminary Schematic 2Nov2005

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Design – Preliminary Bill of Materials

Design – Worn Unit Model

Feasibility: Zigbee communication and accelerometers have been used in

similar applications. Signal processing has been accomplished by one of the team

members in the past on accelerometer data. Antenna design is a new area for all team members providing some

concern. The team will get help from Dr. Venkataraman in designing the antenna.

Without a pure way of accessing the battery life there exist some concern in meeting a long life (preliminary calculations have been accomplished).

Board layout has been accomplished by two team members in the past, but there is some intrinsic difficulties in any board layout.

The design uses devices that have been previously tested on humans, so no foreseen implications from this testing are expected.

Implementation Plan

1. Use the evaluation board that includes the accelerometer unit and the transceiver to develop software code for the microcontroller on the worn unit.

2. Develop software code for the microcontroller on the base unit.3. Breadboard the worn unit to validate the accuracy of the design.4. Assemble a prototype worn unit and perform “in house testing”.5. Make a preliminary printed circuit board layout for the worn unit.6. Develop a preliminary seizure detection algorithm to process the

seizure data.7. Upon approval from RIT/U of R IRB Review Boards, implement

human testing and capture data.8. Using the collected seizure data validate the accuracy of the

preliminary seizure detection algorithm.

Summary Team members gained significant knowledge on seizure types and

possible detection techniques.

The preliminary design of the seizure monitoring system has been accomplished. As the ZigBee evaluation kit will be used for initial data acquisition, there may be some changes to the design.

Upon assembling and testing a prototype, consideration of modifying the design will be made based on the test results and the functionality of the system to meet the desired outcome.

Data collection will be orchestrated early in Senior Design II at Strong Memorial Hospital.

A low level algorithms for detection will be written and then tested once the seizure data has been collected. Some changes may occur based on the test results.

Acknowledgements:

Dr. Phillips

Dr. Berg – Director of Center for Epilepsy at Strong Memorial Hospital, Rochester, NY.

This material is based upon work supported by the National Science Foundation under Award No. BES-0527358.

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