professor taikang ning and professor deborah fixel · 2019-12-20 · research poster presentation...
TRANSCRIPT
RESEARCH POSTER PRESENTATION DESIGN © 2015
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The traditional stethoscope is a tool used to hear a heartbeat. The figure
below is a traditional stethoscope with the various parts labeled. The main
components to note on the traditional stethoscope are the bell, the tubing
and the earpieces.
In a traditional stethoscope, the heart sound travels from the bell to the
earpieces through the tubing. The earpieces of the traditional stethoscope
force one to rely on human hearing to detect various heart sounds,
including heart murmurs. This can be difficult using only this sense
because, human hearing is subjective. For example, if a doctor is told that
there is a heart murmur, they are more likely to hear one, even if one does
not exist. With human hearing, it is possible that one doctor will hear a
murmur and one will not, which can cause confusion and be unnerving for
a patient. The traditional stethoscope is limited to one listener. To get a
second opinion using the traditional stethoscope, another doctor has to
come into the room in the presence of the patient, which can cause anxiety.
To improve the traditional stethoscope we want to replace the earpieces
with a microphone. The addition of a microphone means that we now have
an electrical signal for the heart sound. This electrical signal can be
displayed, making it clear if a heart murmur exists or not.
Introduction
Problem Statement
Our design, the wireless electronic stethoscope, aimed to collect a signal
directly after the bell and wirelessly transmit it to a display. The visual
display of a sound signal eliminates the subjectivity of human hearing. In
our project, we updated the design of the traditional stethoscope by
removing the earpieces and tubing and replacing it with a microphone. The
signal from this microphone was then amplified to a high enough voltage
to be read by a microprocessor. The signal was also passed through a filter
before it was fed into the microprocessor. The microprocessor was used to
convert the signal from analogue to digital and then display the signal on
the LCD. Wireless transmission protocol then allow the signal to be sent
via Bluetooth to a host computer or mobile device. Ultimately,
redesigning the traditional stethoscope using modern technology will allow
for a visual representation of the heart sound, which eliminates the
subjectivity caused by using the traditional stethoscope.
Our Design
Microphone: The microphone was chosen based on two specific
parameters, the first being size. The microphone was chosen to fit within
the tubing attached to the stethoscope bell. Additionally, the microphone
was chosen because it operates within a frequency range which includes
the frequency range of heart murmurs, which is 75 to 1500 Hz. For this
project, a signal in the range of volts is desired, but the microphone
outputs a weak signal in the range of only 10s of millivolts. Therefore, the
signal needed to be amplified by about 100.
Results
IntegrationAll components of our project works separately but we faced problems integrating the
whole system. We were able to pass a signal through the whole system, but
it was not amplified to the level it was expected to. The integrated circuit
is seen below to the left, while the signal passed through the whole system
is displayed on the LCD below to the right.
References1. http://midlevelu.com/blog/anatomy-stethoscope (stethoscope)
2. http://www.analog.com/media/en/technical-documentation/data-
sheets/AD621.pdf (instrumentation amplifier)
3. http://www.electronics-tutorials.ws/filter/filter_4.html (bandpass filter)
4. http://www.cui.com/product/resource/cma-4544pf-w.pdf (microphone)
AcknowledgementsTrinity College Engineering Department
Faculty Advisors: Professor Taikang Ning and Professor Deborah Fixel
Engineering Department Technician: Andrew Musulin
Engineering Department Chair: Professor John Mertens
Heart murmurs are whooshing or swishing sounds during your heartbeat
cycle made by turbulent blood in or near your heart. Assuming 75 beats per
minute, a heartbeat cycle lasts for 0.8 seconds. This is a very short time
interval and can lead to heart murmurs misdiagnosis when using a
traditional stethoscope. Hence, the goal of this senior design project is to
use modern technology to improve a traditional stethoscope into a wireless
electronic stethoscope.
Professor Taikang Ning and Professor Deborah Fixel
Victoria A. Baez, Courtney B. Driscoll, Monica C. Mhina
Wireless Electronic Stethoscope
Goals and Objectives
The main objective of this project is to use modern technology to improve
a traditional stethoscope. To do so, several specific goals were set:
• Eliminate the stethoscope tubing in order to collect the least distorted
signal possible; collect the signal directly after the bell
• Replace the earpieces with a microphone that will collect the heart
sound from the bell
• Amplify the signal from the microphone to the range of volts
• Filter the signal so that only signals within the desired frequency range
are considered
• Convert the signal from analog to digital before the signal is sent to the
LCD Display.
• Wirelessly transmit the signal. This goal will be broken down into two
parts:
• Create a transmission protocol to send signal to one or
many host devices
• Create an encryption protocol to protect the signal
• Receive the transmitted signal and store it on a host computer or mobile
device
Materials102 1721 ND Microphone
• frequency range 20Hz to 20KHz
• Lightweight, 0.8g, and small in size, 9.7x4.5mm
AD621 Instrumentation Amplifier
• Pin strappable gains of 10 and 100
• low input bias currents low noise when operating from high source
impedances
Passive Band Pass filter
• adjustable bandwidth
ARLCD Display
• compatible with Arduino
• 16 bit microprocessor and 320x240 resolution
TinyShield Bluetooth Low Energy Board
• integrated Bluetooth Smart stack
• compatible with Arduino
• ultra compact weight and size, 20x29mm
Instrumentation Amplifier: An instrumentation amplifier was designed
to yield a gain close to 100. To obtain a gain of 100, pin 1 and 8 of the
AD621 were connected. Below to the left is the top view of the
instrumentation amplifier AD621 chip schematic. Below to the right is the
instrumentation amplifier circuit built on the breadboard using the
instrumentation amplifier chip AD621.
In the following oscilloscope figures, the input and output of the
instrumentation amplifier was displayed. To the left, an in input of
36.00mV was fed into the instrumentation amplifier. To the right, the
output of the instrumentation amplifier was 3.841V, demonstrating a gain
of 100 was achieved.
Bandpass Filter: The Band Pass Filter was designed with a lower cutoff
frequency of 75Hz and higher cutoff frequency of 1500Hz. The circuit was
built using experimental values of C1 =105.70nF and R1= 21.3kΩ for a
lower cutoff frequency of 1517.5Hz. The figure below to the left is the
schematic diagram for the bandpass filter. The of 70.60Hz; and C2=
0.95nF and R2 = 110.4kΩ for a higher cutoff figure to the right is the
bandpass schematic implemented on a breadboard.
Analog to Digital Conversion (ADC): The Arduino microprocessor can
perform 10-bit ADC. While reading an analog range of 0-5 Volts, this
allows for a 4.8 millivolt resolution.
The code sampled the analog signal every 0.3 milliseconds, which is a
sampling rate of 5000 Hz. Nyquist frequency is the absolute minimum
frequency the signal can be sampled at, without distorting it. The Nyquist
frequency is defined as 2*Fmax, where Fmax is the maximum frequency
present in the signal being sampled. Since heart murmurs reach up to
1500Hz, the Nyquist frequency of our project is 3000Hz. Our sampling
rate, 5000Hz, is well above the Nyquist frequency, and we can be
confident that our signal is not distorted due to ADC.
LCD Display: Heartbeats occur around 60Hz, or one beat per second.
The LCD was designed to show two beats at a time, covering a span of
approximately 2 seconds. A known sine wave from the function generator
was fed into the LCD Display to test its functionality. The expected sine
wave display is shown below.
In the figure below to the left is the microphone circuit and biasing circuit
schematic. The circuit below in the center shows the microphone circuit
built on the breadboard. The oscilloscope graph below to the right shows a
microphone reading where the microphone is able to pick up a weak signal
of 40.00 mV.
The graph to the right is a Bode Magnitude vs. Frequency plot to
characterize the bandpass filter.
Our design has the potential to improve lives through early diagnosis of
heart murmurs. However, implementation of a Wireless Electronic
Stethoscope is more important since it uses simple electrical devices to
achieve the goal. Since the integrated system is made of different
components whose performance depends on the performance of the
previous component, getting the desired output from each component is
crucial. To ensure expected results from the integrated system of the
Wireless Electronic Stethoscope, better ways to improve the amplification
of the signal collected by the microphone can be employed. In addition,
devising a method to record the received signal after wireless transmission
would be beneficial to the user of our product. Lastly, improvements can
be done on compactness of the system and an overall packaging can be
designed.
Future Improvements
Transmission: TinyShield Bluetooth Board was to able to connect to a
mobile device. The Bluetooth was setup up for UART communication in a
client-server configuration. An Android mobile app was created to receive
and display the signal, but has yet to be tested.