1. Final Design Review for
MedPhone, Inc.:
The MedBox
TOBENNA ANENS, KHALID ETEER,
ASHWIN KUMAR, MARKAN PATEL,
ANIRUDH VINNAKOTA
CLIENT: DR. MARK KAPLAN
April 30th, 2015
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Background: Auscultation
Auscultation (n): “the act of listening to sounds arising within organs as an aid
to diagnosis and treatment.” from Merriam-Webster
● Different types of sounds are present in the chest cavity
o Low-pitch and high-pitch
● Multiple diseases that can be diagnosed with the help of auscultation
o Heart murmurs
▪ 10% of all adults in the US [1]
o Heart arrhythmias
o Rales & ronchi
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Our Project Scope
Our project objectives were, in order of priority, to create a
proof-of-concept prototype specifically for use in isolation
rooms that will show we can
1. Amplify and output internal body sounds
2. Be easily cleanable by existing disinfectant solutions
3. Not interfere with wireless hospital technology
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Critical Design Specifications
Requirement Specification Justification Priority
Acquire and filter the
signal
Filter a range of 20 - 1000 Hz Heart and lung sound frequencies are within this range. [2] 1st
Amplify and output
sounds for multiple
people
Maximally outputs > 75 dB Since our intended target market are isolation rooms, conversations and
ambient noise ≅ 65 dB [3], and sounds over 75 dB may cause discomfort.
2nd
Resists damage from
cleaning
Thickness difference before after 100
cleanings of 10% bleach and alcohol
< 0.1%
10% bleach and alcohol are common hospital cleaning disinfectants 3nd
Maintain a short delay < 200 ms The delay between signal transmission and projection should be less than 200
ms, which is the preferred standard for latency in telephone calls as it is not
detectable by people. [4]
4rd
Preserve quality from
input to output sounds
R2 correlation between maximum
amplification theoretical signal and
experimental signal should be > 0.9
Professional opinion survey, with average
rating must be equal or greater than
standard stethoscope (n = 5)
We want to ensure the quality is preserved during amplification. R2 of above
0.9 is a good measure.
User surveys are a good indication of quality of product
5th
Easy to use and clean Average rating must be equal or greater
than standard stethoscope (n = 10)
User surveys provide evidence of the quality of a product that should
outcompete existing technology.
6th
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Concerns from Paper Design Review
Concern Change Made
Ambient noise from microphone
placed next to diaphragm
Selected a smaller microphone to fit
snugly inside neck of diaphragm
piece
Testing of the electrical design Validated tests of the electrical design
with frequency response curves
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Device in its Environment
● Device will be wall-mounted
● Will rest in space between
outlets and bed
● Cord will be able to reach
patient no matter position on
bed
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How We Acquire Sound
● Sound waves are
mechanical waves
● Diaphragm funnels sound
waves to microphone
● Electret microphone
transduces mechanical
energy to electrical energy,
needs power to do so
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Circuit Diagram
Stage 1:
Pre-Amplifier (Gain 200x)
Speaker
Output
Microphone
Input
LED Light
Stage 2:
Bandpass Filter
(Gain 10x, Passband:
20-200 Hz for Heart,
100-1k Hz for Lung)
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Key Specifications
Design Features
1. Circuit design can theoretically filtering range to
capture heart and lung sounds range of 20 - 1000 Hz
2. Speaker can output up to 75 dB
3. ProJet Acrylic Resin withstands bleach and 10%
alcohol after 100 washings.
4. Everything is hardwired, should experience minimal
delay (<200 ms)
5. Preamplification and filtration from 2 bandpass filters
ensures high quality signal.
6. Made of lightweight acrylicShould be < 3 lbs.
Handheld = ~1.5 lbs
Critical Requirements
1. Acquire and filter the signal
2. Amplify and output sounds for
multiple people
3. Resists damage from cleaning
4. Short delay
5. Signal quality
6. Weight
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Materials (1 of 2)
Component
Housing for circuit
components
Sound capture system
Microphone
Material
3D Printed ProJet Acrylic
Resin
Aluminum Dual-Head
Stethoscope
CUI Inc CME-1538 Electret
Condenser Microphone
Justification
Strong, non-porous, non-reactive
(alcohol, bleach)
Industrially used for electronic
stethoscope applications
Frequency range 20 - 20k Hz,
Captures heart and lung sounds
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Materials (2 of 2)
Component
Audio Cable
Flashlights
Speaker System
Material
10 Foot Redco 4 Channel
Audio Cable
SparkFun Super White LED
Dell A215 Speakers
Justification
High quality insulation between
each conducting line
Outputs ~15 lumens,
> requirement of 10 lumens
(standard medical flashlight)
>75 dB volume, excess of
isolation noise level of 65 dB,
bass frequency of 60 Hz
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1st Iteration: MRSAnary 2nd Iteration: Stethophone
Bulky Non-functional
Difficult to handle Volume dial difficult to reach
Fragile material (failed drop test) Loose acoustic piece
4 second delay because of Bluetooth
wireless transmission
Back plate not firmly secured to rest of
body
Limitation on Past Iterations
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Improvements on Past Iterations
● Wired
● No latency
● Flashlight
● Projected diaphragm
● Speakers output low
frequency sounds
● Capture lung sounds
● Higher volume
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User Operation*
The expected user operation procedure is the following:
1. Turn on the MedBox with a switch located on the mounted box.
2. Remove the handheld piece from its tray on the box compartment.
3. If necessary, change the frequency option by using the button located on the box.
4. Place the diaphragm piece on the patient’s thoracic cavity
5. If necessary, adjust the volume by using the dial on the handheld device
6. Further adjust the volume piece as desired.
7. If necessary, turn on the flashlight by using the button on the top of the handheld
device.
*Recommend operation by health professionals only
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Design Changes Since Paper Design Review
● Change from piezoelectric microphone to electret microphone
○ Piezoelectric microphone picks up applied pressure.
○ Piezoelectric microphone has components on the surface that prevent it from being
cleanable.
● Change from Cardionics diaphragm to aluminum dual-head stethoscope diaphragm
○ Cardionics diaphragm opening did not create good seal for microphone, aluminum dual
head diaphragm did.
● Redesigned and slimmed down handheld casing
○ Was bulky and expensive, now sleek and cheap.
● Moved frequency button to box
○ Button controls circuit in box.
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Engineering Analysis (2 of 4):
Finite Element Analysis
● Need to ensure that the
case will not
permanently bend with
force applied upon
application
● Applied a force between
1 - 6 lbs. at neck of
casing downwards
towards the body
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Engineering Analysis (4 of 4):
Finite Element Analysis
● Force above 4.85 lbs
applied directly to the
neck may cause
permanent bending
damage to the casing.
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Overview of
Validation/Verification Tests (1 of 3)
Criteria Test Summary Pass Criteria
Sound acquisition* Input pure sine frequencies between 20-200
Hz & 100-1000 Hz, measure frequency
response with output voltage determine if
circuit passes this range
Full circuit has a passband of
20-200 Hz for heart sounds,
and 100-1000 Hz for lung
sounds, within 20% tolerances
Amplify and output
sounds for multiple
people*
Measure ≥ 5 individuals’s heart sounds
(both lub and dub). Record with sound
meter outputted sounds standing 3 ft away
from speaker.
Both sample means for heart
sounds > 75 dB
Resists damage from
cleaning*
Wash backplate of Projet acrylic material
100 times with hospital disinfectant, and
record changes.
Thickness percent change
(ΔL/L) < 0.1% after 100
cleanings
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Overview of
Validation/Verification Tests (2 of 3)
Criteria Test Summary Pass Criteria
Short delay* Survey >= 5 participants on the nature of the delay
observed.
Compare timestamps of output waveform and input
waveform
Have “no delay” for all 5/5 surveys
Should experience minimal delay (
<200 ms)
Signal quality Measure the average R2 correlation between maximum
amplification theoretical signal and experimental signal for
signal inputted between frequency ranges for heart and
lungs (20-200 Hz, 100-1000 Hz).
Mean R2 for both filter set-ups ≥ 0.5
Ergonomic
size
Conduct an ergonomic survey on medical professionals
using both the MedBox and current disposable stethoscope.
Compare statistically with paired t-test
Reject the null hypothesis that the
means for the survey results of the
MedBox and disposable stethoscope
are the same at an α = .05
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Overview of
Validation/Verification Tests (3 of 3)
Criteria Test Summary Pass Criteria
Usability Conduct a usability survey on medical professionals
using both the MedBox and current disposable
stethoscope. Compare statistically with paired t-test
Reject the null hypothesis that the
means for the survey results of the
MedBox and disposable
stethoscope are the same at an α =
.05
Weight Measure handheld device on a scale. < 1.5 lbs
Illumination Measure power wattage applied to light to calculate
associated lumen output
> 10 lumens
Electrical Safety Compare with IEC 60601-1 standards Meet IEC 60601-1 standards [3]
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Sound Acquisition (1 of 5): Purpose
● Validate we can effectively acquire and filter low-amplitude signals
for heart sounds (20-200 Hz) and lung sounds (100-1000 Hz)
● Verify we can obtain a frequency response curve for both heart and
lung acquisition
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● Input 9 pure sine wave audio file at frequencies from
○ between 20-200 Hz for heart sounds
○ between 100-1000 Hz for lung sounds
● Played sounds from at 75 dB to speaker ~20 cm away from microphone.
● Recorded input and output from LabVIEW
● Divide peak-to-peak voltage for output by peak-to-peak voltage for input
Sound Acquisition (2 of 5): Methods
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Sound Acquisition (4 of 5):
Results Failed
● Frequency response curve plotted
against gain (dB)
● Cutoffs for lung sounds:
111.36 - 209.7 Hz
● Anticipated cutoffs were thought to be
100-1000 Hz
● High pass is off by 11.36%
● Low pass is off by 283.9%
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Sound Acquisition (5 of 5):
Results Failed
● Frequency response curve plotted
against gain (dB)
● Cutoffs for heart sounds:
76.78 - 302.66 Hz
● Anticipated cutoff:
20 - 200 Hz
● High pass is off by 11.36%
● Low pass is off by 283.9%
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Amplification (1 of 3): Purpose
● Validate that our product can amplify low-amplitude sounds to a
level that multiple people can hear
● Check if we can output a sound > 75 dB (10 dB above that of
isolation room ambient noise level)
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Amplification (2 of 3) - Methods
● Measured heart sounds for 5 random individuals with full circuit
apparatus turned on
● Recorded sound outputted from speaker 3 ft away from the
speaker with Sound Meter Lite application.
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Amplification (3 of 3): Results Passed
Both sample means were > 75 dB.
S1 Loudness
(Lub, Closing of AV valves)
S2 Loudness
(Dub, Closing of Semilunar valves)
● 77.8 ± 0.8 dB 79.8 ± 0.8 dB
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Resist Damage from Cleaning (1 of 2):
Purpose
● Validate that our product can be cleaned in its intended
environment
● Check if prototype withstand harsh cleaning agents used in
isolation rooms
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Resist Damage from Cleaning (1 of 2):
Methods
● Wipe surface the thickness of our handheld (made of Projet acrylic
resin) with 10% v/v alcohol
● Wait for material to dry before proceeding to next wipe
● Measure the thickness of the piece with calipers after wipes
○ 0
○ 50
○ 100.
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Resist Damage from Cleaning (2 of 2):
Results Passed
● No appreciable
degradation noticed or
measured with
calipers (rated for a
resolution of 0.01 cm).
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Signal Quality (1 of 4): Methods
● Validate our product does not introduce noise into the signal before
output and make diagnosis from auscultations difficult
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Signal Quality (2 of 4): Methods
● Input 9 pure sine wave audio file at frequencies from
○ between 20-200 Hz for heart sounds
○ between 100-1000 Hz for lung sounds
● Played sounds from at 75 dB to speaker ~20 cm away from microphone.
● Recorded input and output from LabVIEW
● Calculated R2 coefficient between input x expected gain the output
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Signal Quality (3 of 4):
Results for the Heart Filter Passed
● R2 plotted against the frequency
range of passband of heart filter
● Slight dip at ~120 Hz, leading to
possible lessened signal-noise ratio
● Sample mean of R2 value within the
passband = 0.713
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Signal Quality (4 of 4):
Results for the Lung Filter Failed
● R2 plotted against the frequency
range of passband of the lung filter
● Signal to noise ratio introduced as
you move away from the passband
● Lessened signal to noise also
observed within passband
● Sample mean of R2 value within the
passband = 0.258
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Short Delay (1 of 3): Purpose
● Validate that our product will not lead to user dissatisfaction and
potential misdiagnosis due to excessive latency
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Short Delay (2 of 3): Methods
● Qualitative assessment
● Recruited 5 random participants (n =5) in the Lurie Biomedical Engineering
Building
● Tapped the membrane of the diaphragm piece 3x and listened to output
● Asked to elect one of the following:
○ No delay
○ Some delay
○ Significant delay
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Short Delay (3 of 3):
Results Passed
● 100% of subjects elected “No delay”
● Anticipated because of hard-wired components
● More quantitative assessment to follow
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Device Ergonomics (2 of 3): Methods
● Conduct a survey with 10 medical professionals (n = 10)
● Asked subjects to handle a standard disposable stethoscope first for ~2
min. and prompted them with questions
● Later, asked subjects to handle the handheld portion of the MedBox and
prompted them with questions
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Device Ergonomics (3 of 3):
Results Passed
● Performed a 2 sample
paired t test between the
responses for each
question.
● p values were significantly
below our alpha value of
0.05 for question one and
question three
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Usability (1 of 2): Purpose
● To ensure the device is intuitive to use for medical professionals and that the signal quality of the
device is comparable to existing technology
● To do this, we will conduct a usability survey. We will ask medical professionals to use a
standard disposable stethoscope, the technology currently used in isolation rooms, and have
them take our survey. After, we will have them use the MedBox and conduct the same survey. A
one sided two sample t-test with a α of 0.05 will then be used to statistically analyze the surveys.
The null hypothesis is that both devices are the same, while the alternate hypothesis is that our
device is better.
● We will ask three physicians.
● The test is passed if the null hypothesis rejected at α of 0.05
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Usability (2 of 2): Methods
● Conduct a survey with 3 medical professionals (n = 3)
● Subjects donned a white coat and wear gloves prior to entering the room
● Asked to treat a teammate who acted sick
● Subjects used a standard disposable stethoscope first to auscultate the
chest. Subjects then asked questions from survey
● Subjects then used the handheld portion of the MedBox and prompted with
the same questions
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Usability (2 of 2): Results
● Three medical students surveyed, results
showed no significant difference between the
MedBox and disposable stethoscopes for any
questions
● Because of 2 tailed test, MedBox responses
were significantly lower than stethoscope
responses either
● Mean score for our device were slightly
higher than the disposable stethoscopes
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● Weighed handheld device without the cord a scale
● Measured 0.32 lbs.
● Lighter than previous iteration prototype (0.44 lbs.)
Weight (2 of 2): Methods & Results
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Validation Results (1 of 3)
Test Design Specification Results Conclusion
Sound Acquisition Filters from ranges of 20 – 200
Hz and from 100 – 1000 Hz,
with a 10% tolerance
Did not meet bandpass regions with respect
to both heart (76.8 - 302.7 Hz) and lung
(111.36 - 209.7) sounds within the given
tolerances
Failed
Resists Damage
from Cleaning
Mean thickness percent change
(ΔL/L) < .1% after 100
cleanings with 10% alcohol and
bleach solutions.
Thickness reduction < 0.001% Passed
Signal Quality Average R2 > 0.5 for both heart
sounds and lung sounds filters
Mean heart sounds filter
R2 = 0.716
Mean lung sounds filter
R2 = 0.258
Passed
Failed
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Validation Results (2 of 3)
Test Design Specification Results Conclusion
Device
Ergonomics
Mean score of ergonomics survey questions
for MedBox ≥ that of disposable stethoscopes
2 sample paired t-test with α of 0.05
showed that one handed movement
and accessibility were significantly
better than disposable stethoscopes.
Pass
Usability Mean score of usability survey questions for
MedBox ≥ that of disposable stethoscopes
2 sample paired t-test with α of 0.05
showed that sound quality, diagnostic
usefulness, intuitiveness, and
cleanability were not significantly
different than disposable
stethoscopes
Pass
Illumination LED light between 10-15 lumens at 90
degrees normal to the light
15.43 lumens, based on LED
specifications
Pass
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Validation Results (3 of 3)
Test Design Specification Results Conclusion
Output Volume Speaker output volume ≥
75 dB 1 meter away
during S1 and S2 of
heart sounds
Speakers output mean
78 dB for S1 and 80 dB
for S2
Pass
Short Delay “No delay” assessment
provided by all users
surveyed
All 5/5 users surveyed
confirmed “no delay”
assessment
Passed but pending for
quantitative assessment
Electrical Safety Device adheres to IEC
60601.1 standards
We did not have time to
contact this company
Pending
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Validation Completion
● Short Delay
○ Future testing would use software packages and LabView VI’s specifically designed
for this application.
● Electrical Safety
○ Keystone compliance would perform an electrical safety test and report back to us.
○ For a fee, they will determine if our device has earned IEC 60601 certification via
their website http://www.keystonecompliance.com
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Design Modifications for Failed Specifications:
Sound Acquisition
● Passed this specification on our breadboard but not on our PCB with soldered
connections
● Soldered connections between the capacitor components, double-pull double-throw
switch (DPDT), and cables running from PCB to switch.
● Future Recommendations: Make soldering easier by...
○ Testing different switches for ease of soldering.
○ Designing slightly larger PCBs.
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Design Modifications for Failed Specifications:
Signal Quality
● Future Recommendation:
○ use Harvey Mannequins, programmable human
dummies that produce different cardiac pure
tone sine waves.
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Design Limitations Next Steps:
Single Rail Voltage
● Our op-amp requires two power rails, not
many cheap double rail AC/DC
converters on market.
● Future recommendation: use good quality
single rail op-amps, like the OP291
operational amplifier.
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Design Limitations Next Steps:
DC Rectifier
● Future Recommendation: use a “cleaner” power supply with minimized
ripple noise, although may be more expensive.
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Design Limitations Next Steps:
Piezoelectric Microphone
● Piezoelectric materials amplify applied pressure, compared to electret microphones which
amplifies acquired sound.
● Outputted sound changes as the user applies pressure of the handheld on the patient’s
chest, due to the nature of the piezoelectric material.
● Future Recommendation: use agar gel or other similar gel materials to properly stabilize
and mechanically couple piezoelectric microphone to diaphragm, but to allow for some
movement to pick up internal sounds.
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Design Limitations Next Steps:
Frequency Button On Handheld
● We moved the frequency switch to the box, as it controls the local circuit in the box.
● Future Recommendations:
○ Use a single rail op-amp, like the OP291 operational amplifier, to help free up a
cable in the four channel cable for the switch to use.
○ Use the Redco TGS-08 8 channel cable to accommodate frequency switch
cables.
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Design Limitations Next Steps: Audio Feedback
● Feedback is virtually unavoidable with any audio
system, since we have a diaphragm and
microphone input, and a speaker output.
● Future Recommendation:
○ use a diaphragm with a good seal, like the
3M Littmann Cardiology III Black 22
Stethoscope Diaphragm.
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Design Limitations Next Steps:
Better Bandpass and Notch Filters
● We use a simple bandpass filter, the dropoff after the cutoff frequency is not as
steep as it could be.
● Future Recommendations:
○ Use high order (3rd or greater) Butterworth filter.
○ Use notch filter to eliminate 60 Hz noise.
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Design Limitations Next Steps:
Lung Sound Quality
● Future Recommendations: To better acquire lung sounds...
○ Use a superior diaphragm, like the 3M Littmann Cardiology III Black 22
Stethoscope Diaphragm
○ Use more sensitive microphone, like Panasonic WM-67D Electret Condenser
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Design Limitations Next Steps:
More Ergonomic Handheld Casing
● Our casing is rectangular and has corners and edges.
● Future Recommendations: To make a more ergonomic design…
○ Eliminate corners and edges to accommodate the user’s fingers with grooves
○ Add strips of rubber in these grooves for better grip on the handheld.
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Conclusion
● Our casing is rectangular and has corners and edges.
● Future Recommendations: to make a more ergonomic design…
○ Eliminate corners and edges to accommodate the user’s fingers with
grooves
○ Add strips of rubber in these grooves for better grip on the handheld.
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References
1. Swierzewski, Stanley J. "Heart Murmur Overview." - Heart Murmur. Health Communities, 19 Nov.
2008. Web. 01 Feb. 2015.
2. "Toolkits." Electronic Stethoscopes. N.p., n.d. Web. 30 Jan. 2015.
3. "Decibel (Loudness) Comparison Chart." Decibel (Loudness) Comparison Chart. N.p., n.d. Web.
30 Jan. 2015.
4. Percy, Alan. “Understanding Latency in IP Telephony”. Brooktrout Technology.
http://aitel.hist.no/fag/ipt/lek02/iptel_latency_brooktrout.pdf
5. "Light Output Measurements." - Flashlight Wiki. N.p., n.d. Web. 02 Feb. 2015.
6. "IEC 80001-1:2010." ISO. IEC, n.d. Web. 03 Feb. 2015.
<http://www.iso.org/iso/catalogue_detail.htm?csnumber=44863>.
7. "Common Cold." Humidifiers. N.p., n.d. Web. 30 Jan. 2015.
8. Moritz AR Henriques FC Jr. Studies of thermal injury II: The relative importance of time and
surface temperature in the causation of cutaneous burns. Am J Pathol. 1947; 23: 915-941.17.
"Average Hand." Size. N.p., n.d. Web. 02 Feb. 2015.
9. "Acrylic Typical Properties Generic Acrylic (PMMA)." Acrylic Typical Properties Generic Acrylic
(PMMA). Prospector, n.d. Web. 18 Mar. 2015.
10. "U.S. Food and Drug Administration." Medical Device Data Systems, Medical Image Storage
Devices, and Medical Image Communications Devices. N.p., n.d. Web. 02 Feb. 2015.
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User/Stakeholder Requirements
Attribute Specifications Justification
Amplify and output sounds for
multiple people
Outputs up to 75 dB Isolation room ambient noise ≅ 65
dB [3]
Resist damage after cleaning No visible material damage after
exposure 10% bleach and alcohol
(after 100 cleanings) & still passes
quality test
10% bleach and alcohol are potent
hospital cleaning disinfectant
Short delay < 200 ms Preferred standard for latency in
telephone calls is 200 ms, since it is
not detectable by humans [4]
Illumination >10 lumens Standard medical flashlight
brightness averages between 10-15
lumens.[5]
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Functional Requirements
Attribute Specifications Justification
Can amplify signals of multiple
frequencies
Amplifies frequencies within 20
– 1000 Hz
Heart and lung sound
frequencies are within this
range. [2]
Cannot interfere with existing
hospital equipment
Complies with IEC 80001[6] IEC 80001 defines
technologies that may interfere
with other hospital equipment
Adjustable range of
amplification
Can amplify sounds
at least 50x of the input
The sound will be audible to
multiple people at volumes of
their liking
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Environmental and Interface Requirements
Attributes Specification Justification
Biocompatible Biocompatibility ISO 10993-10 ISO 10993 is a commonly used
industry standard for biocompatibility.
Easy to use and clean Average rating must be equal or greater
than standard stethoscope (n = 3)
User surveys are good indication of
quality of product
Ergonomic and grip optimization Average rating must be equal or greater
than standard stethoscope (n = 3)
User surveys are good indication of
quality of product
Operability in different
temperatures and humidities
Functions in room temperature ± 20°F
and up to 50% humidity
Rooms may be humid for sick
patients [7]
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Performance, Safety, and Quality Requirements (1 of 2)
Attribute Specification Justification
Quality R2 correlation between maximum amplification
theoretical signal and experimental signal for both
filters should be > 0.5
Professional opinion survey, with 9/10 professionals
prefer over typical disposable stethoscopes.
We want to ensure the quality is
preserved during amplification. R2 of
above 0.5 is an attainable measure
that still provides good signal quality.
User surveys are good indication of
quality of product.
Device can withstand
falls
< 2 on the damage scale after 4 foot drop test (0-10
damage scale, 0 = no damage, 10 = completely
destroyed), & still functions with a quality test
Auscultations are measured typically
2-4 ft from ground
Electrically safe to
handle
Adheres to IEC 60601-1 standards Physical barrier prevents current
from reaching user or patient
82. 4/29/2015
FINAL DESIGN REVIEW
82
Attribute Specification Justification
External Device
Temperature
Should be ≤ 35° C to the
touch
Above 35° C will cause discomfort, and above
45° C will start to cause burns. [8]
Consistency Should still operate at least 6
months and pass the quality
tests
Dr. Kaplan can use and continue to test the
device with his patients after the final
deliverable.
Diaphragm
Resistant to
Bending
Neck of diaphragm should not
experience above the flexural
yield strength of the material
(acrylic = 33.1 MPa) [9]
The material should not plastically deform
from falling stresses.
Performance, Safety, and Quality Requirements (2 of 2)
