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Document Sample
Pressure Sensor for Peripheral
Neuropathy
Group 19
Pankil Dharia
Zachary Hafez
Mustafa Manzoor
Agenda
Introduction
Objective
Review of Design
Functional Tests
Successes and Challenges
Marketing Factors
Recommendations
Questions
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/rar
e.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
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
Design of the Product
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
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)
Review of Design
Review of Design
Review of Design
Power:
1 8
+9V
0.1u
2 7
MAX1044
Switched-Capacitor
3 6
10u Voltage Converter
10u
4 5
-9V
Output
9V Battery powering entire device
-9V produced by the above circuit
Review of Original Design
Review of Design
Pressure 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
Review of Design
Temperature 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
Review of Design
Review of Design
Operational 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
Review of Design
Review of Design
Comparator Circuit (Pressure):
Circuit uses a comparator with Vref set to 3V
Vref corresponds to the 5lb/(inch^2) threshold
pressure for pain
If input signal >= Vref
– Comparator outputs a logical high to the alarm system
If input signal < Vref
– Comparator output will remain logically zero
Review of Design
Comparator Circuit (Temp.):
If input temp > 50°C
Resistance across Thermistor decreases
Increases current and input voltage to comparator
Triggers comparator to output logical high signal
when input voltage >= Vref (3.12V)
If input temp < -5°C
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) >= input voltage
Review of Design
2K 5.1K
1 8 1 8
Rg Rg Gnd Vcc +9V
2 7 2 7
-In +Vs +9V +In Output
3
AD622AN 6 3
LM311N 6
+In Output -In Bal/Strobe
4 5 +9V 4 5
1.5K
Output to System Design Block
-Vs REF Vee Bal
20K
750
FlexiForce Sensor -9V
Block
560
Pressure Sensor Circuit
Review of Design 1
2K
8
Gnd Vcc +9V
2 7
+In Output
3
LM311N 6
+9V 5K Ohm
Temp.
-In Bal/Strobe
1K
Thermistor
+9V 4 5
5.2K Vee Bal
Sensor 1.1K
-9V
Block
Circuit 1
Rg
2K
Rg
8
1
2K
8
Gnd Vcc +9V
2 7
-In +Vs
2 7
AD622AN +9V +In Output
3 6 20K
+In Output
3
LM311N 6
-In Bal/Strobe
4 5
-Vs REF
1K 4 5
Vee Bal
-9V
Block -9V
Block
Output to L-O-S Block
Output to L-O-S Block
(Cold)
(Hot)
Review of Design
Review of Design
Latch:
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.
Review of Design
Review of Design
Speaker:
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
Review of Design
LEDs:
Different colored LEDs are used to distinguish
between temp. and pressure
Red coincides to a temperature >= 50°C
Yellow coincides to a temperature <= - 5°C
Green coincides with a pressure >= (5lb/inch^2)
Review of Design
+9V
0
Vcc1
1 16
a1 b1
1 12
Input from Inv. in 2 15
System Design
a2
CD4043BE b2
C2 C1
Block (pressure) 3
a3 b3
14
3 10
4 13
a4 b4
5 12
Switch
a1 b1 4 9
6
a2 b2
11
C4 C3
Input from
7 10 6 7
Comparator Block a3 b3
(Hot) 8 9
a4 b4
GND
0
Pressure
Input from
LED
Comparator Block
(Cold)
10 K
Cold Temp.
Output LED
10 K
Hot Temp. to System
10 K
Latch-Switch- LED Design Block
(NOR gate)
Output Block Output
to System
Design Block
Output
to System
Design Block
(NOR gate)
(NOR gate)
Review of Design Input from
L-S-O Block
Input from
L-S-O Block
Input from
L-S-O Block +9V
Amp-Comparator Block for Pressure (1)
Pressure
1 14
a1 b1
2 13
Amp-Comparator Block for Pressure (2) a2 b2
Overall Sensor
Amp-Comparator Block for Pressure (3)
3
4
a3
a4
SN74LS260N
SN74LS260N
b3
b4
12
11
5
NOR Gate 10
Circuit
a1 b1
System 6
a2 b2
9
Foot
Amp-Comparator Block for Pressure (4) 7 8
a3 b3
Blocks
Design Amp-Comparator Block for Pressure (5)
Block Temp. Sensor Circuit
Comparator Block for Temperature
+9V
1 14
a1 b1
2 13
a2 b2
L-S-O Block
L-S-O Block
3 12
a3 b3
Output to
Output to
(Cold)
(Hot)
4 11
SN74ALS04BN
a4 b4
5
a1 Inverter b1
10
L-S-O Block
(Pressure)
Output to
6 9
a2 b2
7 8
a3 b3
Latch-Switch-Output Block
Speaker
Functional Tests
Pressure
sensor without
amplification
Channel 1:
Input
Channel 2:
Output from
pressure
sensor
Functional Tests
Pressure
sensor with
amp. (Gain = 5)
Channel 1:
Input
Channel 2:
Output from
pressure
sensor
Functional Tests
Comparator
Circuit
Channel 1:
Input to
comparator
Channel 2:
Output showing
logical high
when Vref (3V)
is exceeded by
input signal
Functional Tests
Temp. Input With Corresponding Comparator Output
3
2.5
2
1.5
Volts
1 Comp. Output
Input
0.5
0
-0.5
-1
-0.000006 -0.000004 -0.000002 0 0.000002 0.000004 0.000006
Seconds
Functional Tests
Oscilloscope reading of Thermistor Response
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 -20°C...flame 50°C)
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.
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
Successes and Challenges
Successes and Challenges
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
Successes and Challenges
PCB
Successes and Challenges
PCB
Successes and Challenges
PCB
Marketing Factors
Part Description Quant. Price Part Description Quantity Price
Battery Connection for 9V 2 $1.00 FlexiForce Pressure force 5 $60.00
Connector battery A201-25 transducer (25lb)
Speakers Used to notify user of 1 $5.00 Thermistors Temperature 1 $2.00
dangerous-pressure or NT05-5029 sensor with
temp. variable resistance
LED Light Emitting Diodes 3 $.50 Sock Casing for the 1 $5.00
(green, red) for sensors device
displaying signal to user
Batteries 9V 1 $2.00
Operational Amplifies voltage signal 6 $15.00
Amplifier from sensors Maxim To generate - 9V 1 $2.00
AD622AN Capacitor
Latch Used to keep alarm/LED 1 $.50
CD4043BE on until device is reset PCB Printed circuit 1 $30.00
board
5-input NOR gate Used to determine if a 1 $.50
SN74LS260A signal is on from the 5 TOTAL $136.00
pressure sensors
Inverter Invert output 1 $.50
SN74LS04
Electrical Wire Standard wiring 5 feet $10.00
Resistors Standard resistors $2.00
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
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
Relevant Ethical Issues
Current leakage
– ‘Leakage Current Tests’ are run on medical related
devices for safety
– How much current goes through a person’s 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.
Special Thanks
Professor Chiang Liu (University of Illinois)
Dr. Andrew Reed
Dr. Walid Hafez
Dr. Raymond Fish
ECE Parts Shop Staff
Hyesun Park
Questions
Any Questions?
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