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Measuring Ocular MicrotremorThomas
RutkowskiVivian PhinneySalman Al-Saif
Mark HasemeyerSteve Carroll
Ocular Microtremors (OMT)
-Low-amplitude, high-frequency tremors of the eye. (20-100Hz)
-Caused by random, ground-state signals on oculo-motor nerves
-Oculo-motor nerves originate in brain stem. OMT indicates brainstem health.
-OMT correlated with patient’s level of consciousness.
-Gives strong indication of the chances of recovery for coma patients.
System OverviewWaveform Generator
OMT Simulator
Sensor (Provided)
Power Supply
Analog Input/
Preprocessing Circuitry
- Amp
Test MUX
Microprocessor with Integrated A/D, UART, and
DSP
Bedside Monitor (Philips MP-
60/70 or Agilent V24/26)
Philips VueLink Module – M1032A
For MCU, currently looking at Atmel AVR32 with 10-bit A/D and integrated DSP functions,50 MHz clock.
System Module Overview
LCD SD Card
16-bit Timer
10-bit A/DUART
Controller
256kB Flash
AVR32UC3B1256 Microcontroller
16Mhz Crystal
PLL – 50 Mhz CPU Clock
Signal Conditioni
ng
Sensor
RealTerm/ Bedside Monitor
3.3 V Power Supply
MAX3380E UART Level
Shifter
SPI Controller
3.5” Graphic LCD
16-bit Parallel Interface
SD Card
Basic CPU Architecture and Connectivity
GPIO Controller
Start Sampling Buffer 0
Wait until Buffer 0 Full (1 sec)
Start Sampling Buffer 1, Start FFT
on Buffer 0
Wait until Buffer 1 Full (1 sec) – FFT on Buffer
0 finishes ~1 ms
Start Sampling Buffer 0, Start FFT
on Buffer 1
Find OMT frequency from FFT output just
completed
Currently using 1024 sample buffer and 1024 kHz sampling frequency, giving 1 second of data in buffer.
Send frequency and waveform
samples to UART(monitor),
LCD, and SD card.
Perform inverse FFT on
frequencies within valid
range. Wait until Buffer 0 Full (1 sec) – FFT on Buffer
1 finishes ~1 ms
Processing Algorithm
Signal Processing – General OverviewUsing FFTs, much faster than DFT
algorithmsAtmel studio has several built in FFT
algorithms that require minimal modification But… it’s not working as we had anticipated
Further work in DSP is needed Just recently got sampling, buffers, and FFT
workingFurther testing required to find optimal DSP
algorithm
Signal SamplingUsing the built in ADC in the Atmel processor to
sample data
The input voltage ranges from 0V to 3.3V (adjustable), the signal needs to be scaled and clamped to avoid causing damage to the processor
Use of a 8:1 voltage divider, or an op-amp circuit with gain K = 0.125, assuming a maximum 12V input from the sensor IC
A 3V zener diode is used to clamp the analog input, or a comparator circuit
Signal Sampling (contd.)-Sensor output is in the range ±12 V
-A/D takes 0 - 3.3 V
-First stage inverts and scales sensor output to ±1.5 V
-Second stage adds 1.5V DC offset for new range of 0 – 3 V for A/D
Signal to be sampledFrequency components at 15Hz, 90Hz, and
165Hz
Signal recreated with MATLAB
0 20 40 60 80 100 120 140 160 180 200200
210
220
230
240
250
260
270
280Sampled Signal, Frequency Content at 15Hz, 90Hz, 165Hz
Vol
tage
[m
V]
Time
FFTAs with other things involving signal processing,
we are currently experimenting with the built in FFT functions
The FFT routines functioned properly with minimal modifications
Going forward, two possible solutions to processing that we are consideringAfter determining the frequency of the OMT signal,
a sinusoidal wave is generated with varying amplitudes proportional to the OMT
Using wavelet processingWe will know more once we’ve done more careful
testing, since our sensor is very sensitive, there is a lot of room for error
FFT (contd.)Filtering and Noise Reduction
As mentioned previously in PDR, the OMT frequency range lies between 40Hz and 120Hz
Use of a high pass filter at 20Hz, and a low pass filter at 150Hz
We identified the main source of noise as that coming from various power lines across the room
A notch filter is used (bandstop) for the frequency range 57Hz-62Hz
Sensor is sensitive, picks up the slightest movement, another sensor might be used to provide a differential solution
The other main artifact that affects the signal is heartbeat and voice, we are still considering solutions to both problems
FFT (contd.)The following slide represents an example of
the same signal sampled aboveWe used the FFT algorithms to represent the
frequency content of the analog signalSimple processing was done to filter out
unwanted frequency content (below 20Hz, above 150Hz, and 60Hz)
The slide after that is a capture of Vivian’s OMT frequency content
0 50 100 1500
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2Fourier Transform of Processed Signal
Ene
rgy
Frequency [Hz]
Processed signal
Captured OMT Signal over 1 Second Interval
We believe that thorough testing and experimentation is very important to the success of our project
After CDR, we will continue with OMT processing
Power ManagementUtilizing a medical grade power supply, since
project is not power centric, plus it is safer to go with this option and avoid any risk or harm to the experimental subjects (basically us)
ELPAC MED113TT, provides three regulated outputs, 5V, ±12V
LP2951 voltage regulator from TI will be used to power the Atmel processor
Power Management (contd.)
Bedside Monitor • Leasing from Medelco
• Lease will include:
Philips MP70 Touch Screen Monitor
M1032A Vuelink Interface Module
M8048A FMS (Flexible Module Server)
M3001A MMS (Multiple Monitoring System)
• Possibly:
M1032A#K66 Cable with DSUB-9 connector
VueLink Cable Pinout Showing UART Tx/Rx Lines
VueLink Connector
DB-9 Connector
Backup Plan - Analog Input Signals
LCD Display
http://www.crystalfontz.com/product/CFAF240320K-T-TS
-Parallel or SPI Interface to LCD- 4-Wire Resistive Touch Panel- Will display small waveform and OMT frequency, in addition to bedside monitor display. -Touch-screen menu may allow user to configure data-logging options, sampling rate, and buffer size.
SD Card Socket Board
http://www.sparkfun.com/commerce/product_info.php?products_id=204
Breakout Board for SD-MMC Cards
Routes SD card pads to solder able through-hole connector.
We will use SPI mode to read/write from card.
Card requires 3.3 V
Data Logging can be started using touch screen menu on LCD.
Risks and ContingenciesBlowing the sensor piezo-transistor or integrated IC amp
Eyetect shipped a backup sensor earlier this week The FFT signal processing algorithm is a concern
Waveform spiky and aperiodic Now that we have the sampling, buffers and basic FFT
working, can test other processing strategies: Wavelets FIR Filters on Buffer followed by Peak-Count Algorithm Statistical Analysis
Product Unit Cost Amount Total Cost Provider
PROCESSING/MANUFACTURING Atmel AVR32 Development Kit 179.00 1 179.00 http://mouser.com/4-layer PCB 66.00 3 198.00 http://www.4pcb.com
Packaging 95.00 2 190.00 http://www.firstcut.com/
INTERFACE Philips M3 Bedside Monitor 600.00/mo. 2.5 1,500.00 http://www.medelco.com/patient_monitors.html
Vuelink M1032A - 1 -
M3001A MMS (Multiple Monitoring System) - 1 -M8048A FMS (Flexible Module Server) - 1 -
Vuelink connector to DSUB9 Cable 175.00 1 175.00 http://www.dotmed.com/listing/594385LEMO Circular Push Pull Connectors 24.92 3 74.76 http://mouser.com/2GB SD Flash Card Model CT2GBSD 7.99 1 7.99 http://www.newegg.com/
Breatkout Board for SD-MMC Card BOB-00204 17.95 3 53.85 http://www.sparkfun.com/ LCD Display - CFAF240320K-T-TS 30.74 3 92.22 http://www.crystalfontz.com/
MEDICAL GRADE POWER SUPPLY Voltage Regulator LP2951_33 (3.3V) 0.96 5 4.80 http://www.newark.com/Surface mount bypass capacitors (25
capacitors) 4.50 2 9.00 http://www.ti.com/Surface mount resistors 0.20 30 6.00 http://www.amazon.com/Power Connector (5-pin) 5.50 2 11.00 JB Saunders
ALPS_SKHUQBO56A Switch 2.00 2 4.00 http://www.allelectronics.com
ADMINISTRATIVE COSTS Printing Manuals 40.00 1 40.00 Poster 12.00/ft. 4 feet 48.00
Rider Insurance Policy for Bedside Monitor 250.00 1 250.00 Shipping/Handling Fees 100.00 2 200.00
MARGIN 7% 213.05
TOTAL COSTS 3,256.67 Outside Funds
OUTSIDE FUNDING EyeTect 3,000.00UROP 800.00
Northrop Grumman 200.00TOTAL FUNDING 4,000.00
Current Budget
Division of LaborTom Vivian Mark Salman Steve
Power
Power Supply X
Powering Sensor X X
MCU
Signal Sampling - A/D X X
DSP of Signal X X X
Interface
LCD Interface on Dongle X
Data Capture on SD Card X X
Condition Sensor Output X X X
Patient Bedside Monitor Interface X X
Manufacturing
PCB X X
Dongle X
Documentation
Technical Manual X X
User's Manual X X
UROP X
Extra (if time)
Data Mining/Trend Evaluation X X
Deliverables
Timeline
Questions?In Order of Appearance:
Tom
Steve
Salman
Mark
Vivian