Pressure Sensor for Peripheral Neuropathy

1
Pressure Sensor for Peripheral Neuropathy

• Group 19
• Pankil Dharia
• Zachary Hafez
• Mustafa Manzoor

2
Agenda

• Introduction
• Objective
• Review of Design
• Functional Tests
• Successes and Challenges
• Marketing Factors
• Recommendations
• Questions

3
Introduction

• People who suffer from peripheral neuropathy are
  left with partial or no feeling in their limbs.
  They often bump or scrape these limbs
  unknowingly, which leads to infection and
  possible amputation.
• According to the Neurology Channel Online
  (http//www.cnn.com/2006/HEALTH/conditions/01/27/r
  are.conditions/index.html), Peripheral Neuropathy
  affects at least 20 million people in the United
  States.
• Nearly 60 of all people with diabetes suffer
  from peripheral neuropathy

4
Objective

• We want to construct a product that senses when
  trauma to the foot has occurred, alerting the
  user of potential injury.
• Pressure sensors will be located on each toe,
  which are the most vulnerable to trauma in
  patients with neuropathy of the foot.
• Temperature sensors will be included to alert the
  user that their skin is in danger
• An alarm and corresponding LEDs will activate
  when a traumatic event is detected by the sensors

5
Design of the Product
6
Objective (cont.)

• Benefits
• Instant notification of possible traumatic event
• Low cost
• Comfortable
• Adjustable
• Light weight and discrete
• Portable
• Commercially recreational
• Reduced probability of dangerous infection
• User friendly

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Objective (cont.)

• Features
• Various pressures and temperatures sensors
• Multiple sensor locations for distributed sensing
• Identification of traumatic event to assess
  possible damage
• Visual output for corresponding notifications
• Distinct sound output (alarm) for dangerous
  pressures and temperatures for audible
  notification
• Adjustable strap for variable location
• Easy to use reset button
• Multi-colored LEDs for differentiating causes of
  trauma
• Battery operated (9V)

8
Review of Design
9
Review of Design
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Review of DesignPower

• 9V Battery powering entire device
• -9V produced by the above circuit

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Review of Original Design
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Review of DesignPressure Sensors

• 25lb. Flexi Force Pressure Sensors(A201-25)
• Sensors placed on each digit
• The pressure exerted on the force transducer will
  vary the resistance in the sensor
• When a certain voltage threshold is reached, an
  alarm will sound with LED notification

Tekscan
13
Review of DesignTemperature Sensors

• Ametherm Thermistor (NT05-5029)
• Sensors placed on the sides of the foot
• As temp. increases, resistance decreases
• When a certain high or low threshold is reached,
  an alarm will sound with corresponding LED
  notification

Ametherm
14
Review of Design
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Review of DesignOperational Amplifier

• Sensors output low voltages in millivolt range
• Operational amplifiers amplify the input voltage
  of the Flexi-force transducer by 50 times to
  about 2-5 Volts
• Output signal sent to the comparator for further
  analysis

16
Review of Design
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Review of DesignComparator Circuit (Pressure)

• Circuit uses a comparator with Vref set to 3V
• Vref corresponds to the 5lb/(inch2) threshold
  pressure for pain
• If input signal gt Vref
• Comparator outputs a logical high to the alarm
  system
• If input signal lt Vref
• Comparator output will remain logically zero

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Review of DesignComparator Circuit (Temp.)

• If input temp gt 50C
• ? Resistance across Thermistor decreases ?
  Increases current and input voltage to comparator
  ? Triggers comparator to output logical high
  signal when input voltage gt Vref (3.12V)
  
• If input temp lt -5C
• ? Resistance across Thermistor increases ?
  Decreases current and input voltage to
  comparator? Input voltage amplified with gain of
  10 ? Triggers comparator to output logical high
  signal when Vref (4.0V) gt input voltage

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Review of Design
Pressure Sensor Circuit
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Review of Design
Temp. Sensor Circuit
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Review of Design
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Review of DesignLatch

• An S/R latch (CD4043BE) is used to hold the
  signal once it has been triggered even after the
  input has been removed.
• Latch will enable the user to reset the alarm
  after being notified.
• The latch will reset the speaker alarm as well as
  the 3 LEDs.

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Review of Design
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Review of DesignSpeaker

• This will output a sound to alert the user of
  hazardous conditions.
• The 3 latch outputs are ORed and sent to the
  speaker
• The speaker is triggered when either latch
  (pressure, cold temp., hot temp.) is set to high

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Review of DesignLEDs

• Different colored LEDs are used to distinguish
  between temp. and pressure
• Red coincides to a temperature gt 50C
• Yellow coincides to a temperature lt - 5C
• Green coincides with a pressure gt (5lb/inch2)

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Review of Design
Latch-Switch- Output Block
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Review of Design
Pressure Sensor Circuit Blocks
OverallSystemDesignBlock
Temp. Sensor Circuit
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Functional Tests
Pressure sensor without amplification Channel 1
Input Channel 2 Output from pressure sensor
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Functional Tests
Pressure sensor with amp. (Gain 5) Channel 1
Input Channel 2 Output from pressure sensor

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Functional Tests
Comparator Circuit Channel 1 Input to
comparator Channel 2 Output showing logical
high when Vref (3V) is exceeded by input signal
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Functional Tests
32
Functional Tests
Oscilloscope reading of Thermistor Response
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Functional Tests

• Pressure Sensor
• Tested in accordance with known pressures that
  cause damage to foot
• Sensors were first aligned to the tip of each
  digit of subject.
• Tested the sensitivity of the sensors, when
  mapped to a specific foot.
• Temperature Sensor
• Exposed to varying degrees of temp. (dry ice
  -20C...flame 50C)
• Power Supply
• Voltage leaks were tested
• Voltages at every component were measured
• Calibration and Reliability
• The pressure sensors were calibrated to injurious
  measurements
• Damaging forces were tested to ensure reliability
  of the circuit.

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Successes and Challenges

• Successes
• Able to run entire device with one 9V battery
• After consultation with podiatrist (Dr. Reed),
  able to achieve specific thresholds
• Able to successfully implement a fully-functional
  model of device

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Successes and Challenges
36
Successes and Challenges
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Successes and Challenges

• Challenges
• Calibrating the circuit to work with precision
• Amplifying the signals coming from temp. and
  pressure sensors
• Figuring an accurate model for testing the
  product
• Using PTC-thermistors instead of NTC-thermistors
• Implementing device on PCB

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Successes and ChallengesPCB
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Successes and ChallengesPCB
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Successes and ChallengesPCB
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Marketing Factors
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Marketing Factors

• Condense Circuit
• Condensing current circuit on 4-layer PCB
  increases cost
• Pressure Sensor Sheet
• Instead of specific points, cover entire foot
• PolyVinylidine DiFluoride (PVDF)
• Increases cost
• Reliability
• Decreasing false positives
• Safer design

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Recommendations

• Programmable ICs
• Integrate amplifier and comparator on one IC
• PCB technique
• Use insulated PCBs to prevent accidental open
  circuits
• Multi-functional Speaker
• Be able to generate different frequency sounds
  for different signals

44
Relevant Ethical Issues

• Current leakage
• Leakage Current Tests are run on medical
  related devices for safety
• How much current goes through a persons body
  when they initially come in contact with the
  device until the current moves to ground.
• There usually will always be some current flow
  however, the amount is what is measured here.
• Prevention
• Low current distributes throughout our circuit.

45
Special Thanks

• Professor Chiang Liu (University of Illinois)
• Dr. Andrew Reed
• Dr. Walid Hafez
• Dr. Raymond Fish
• ECE Parts Shop Staff
• Hyesun Park

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Questions

• Any Questions?