Professor Taikang Ning and Professor Deborah Fixel · 2019-12-20 · RESEARCH POSTER PRESENTATION DESIGN © 2015 The traditional stethoscope is a tool used to hear a heartbeat. The

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.