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RESEARCH ARTICLE
OPEN ACCESS
Manuscript received June 03, 2022; revised September 10, 2022; accepted September 12, 2022; date of publication October 28, 2022
Digital Object Identifier (DOI): https://doi.org/10.35882/ijahst.v4i4.256
Copyright © 2022 by the authors. This work is an open-access article and licensed under a Creative Commons Attribution-ShareAlike 4.0 International
License (CC BY-SA 4.0)
How to cite: Andi Fathkur Rohman, Muhammad Ridha Mak’ruf, Triwiyanto, Lamidi, “Analysis of the Effectiveness of Using Digital Filters in Electronic
Stethoscopes”, Journal of Electronics, Electromedical Engineering, and Medical Informatics, vol. 4, no. 4, pp. 229–234, October. 2022
Analysis of the Effectiveness of Using Digital
Filters in Electronic Stethoscopes
Andi Fathkur Rohman1, Muhammad Ridha Mak’ruf1, Triwiyanto1, Lamidi1, and Phuoc-Hai Huynh2
1 Department of Medical Electronics Technology, Poltekkes Kemenkes Surabaya, Indonesia
2 Faculty of Information Technology, Angiang University, Vietnam
Corresponding author: Muhammad Ridha Mak’ruf (email: ridha@poltekkesdepkes-sby.ac.id)
ABSTRACT The heart sound produced in some cases of the disease shows a specific pattern. This study aimed to design an
electronic stethoscope for cardiac auscultation using digital filter to improve accuracy. This study's contribution is showing certain
patterns that can be diagnosed in the sound signal. So that the pattern can be known when there is a heart disease disorder, an
electronic stethoscope will be made for auscultation of the next display, making it easier for users to diagnose heart disease. The
heart sound is obtained from the heart's mechanical activity, which is tapped by a condenser mic. The heart sound will be held in a
pre-amp circuit, then the filters used are High Pass Filters and Low Pass Filters with an interrupted frequency of 20-95 Hz. The
output of the filter circuit will enter the booster circuit. Then it will be processed by the microcontroller. In processing the data that
will be displayed on Nextion and Speaker, the author uses Arduino Mega. Based on the test, it can be seen that the digital filter has
a slight error rate because it removes the most noise, while in the analog filter there is still a lot of noise. The results of the research
that has been done can be implemented using a system that really supports the needs.
INDEX TERMS Stethoscope, Low Pass Filter, High Pass Filter, Speaker.
I. INTRODUCTION
Technological progress is something that we cannot avoid in
this life because technological progress will run in accordance
with the progress of science. Every innovation is created to
provide positive benefits for human life. Provides many
conveniences and a new way of doing human activities[1][2].
Especially in the technology field, society has enjoyed many
benefits brought by the innovations that have been produced.
The technological revolution in the health sector that has been
achieved to date is a significant feature of modern life[3].
However, the power of technology must be used carefully and
responsibly to ensure that we apply it efficiently and humanely.
Appropriate use of health technology involves mastery of
science, engineering or machine tools and concepts and
knowing economic, ethical, and moral issues [4]. A stethoscope
is basically an acoustic medical instrument used to examine
sounds in the body. One of them is hearing the heartbeat's sound
and detecting abnormalities. The stethoscope was invented in
France in 1816 by a man named René-Théophile-Hyacinthe.
Earpieces, Tubing or Tube, Diaphragm, and Bell. Auscultation
is a technique or method that is most often used by medical
personnel in the initial examination of patients[5]. One way is
to use a tool called a stethoscope. A stethoscope is a simple
acoustic medical instrument that is used to diagnose sounds in
the human body. Medical personnel often use this acoustic
stethoscope to examine heart sounds. One sound that can be
detected is the sound associated with the heart's pumping
activity. Voices claim indication of heart rate and heart rhythm.
The sound is also useful for providing information about the
effectiveness of the pumping activity of the heart and heart
valves. Until now, the clinically used instrument for detecting
heart sounds is the acoustic stethoscope[6]. The heart is the
center of internal blood circulation. The human body has a very
vital role. Without a heart, humans will not be able to live,
because the organs in the body will lack oxygen and die. A
healthy heart is absolutely necessary for a person. Without a
healthy heart, a person will lose their quality of life. Knowing
the rhythm of the heartbeat is one way to maintain a healthy
heart. A heart that works too fast will disrupt the balance of the
body and will also have the same result if the heart works too
slowly[7]. One way to find out the patient's condition is to listen
to sounds from inside the human body, namely through an
instrument called a stethoscope. The process of examining the
sound of respiration or heartbeat is called auscultation.
Problems that occur in cardiac auscultation using a
conventional stethoscope are environmental noise, ear
sensitivity, low frequency and amplitude, and relatively similar
sound patterns. The results of hearing sound are also very
subjective so everyone can interpret the results differently[8].
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Previous research has been made by Carlos Aguilera-
Astudillo et al. to develop a 3D printing stethoscope that is
connected to a Smartphone[9]. The study reads data through a
smartphone and displays a signal to a smartphone. The
weakness of this tool is that there is still a cable connected from
the smartphone to the system. Filter, which functions to pass
the desired signal frequency and hold unwanted signal
frequencies, in the signal extraction process, the filter used can
use an analog filter or a digital filter. The analog filter has a
weakness; namely, there is still a lot of noise during the process
of filtering the respiration rate signal from the ECG signal,
while the digital filter produces less noise compared to the
analog filter[10][11]. This digital filter is better in using the
process of decreasing the respiration rate signal than ECG, and
also the level of accuracy and precision of the digital filter is
more accurate and precise[12][13]. In 2017, Donald L. Hall et
al. made a digital stethoscope that was designed to be
reconstructed from a mathematical model accompanied by the
physical equipment used. After the systematic exploration of
mathematical principles is completed, the working performance
of the instrument is shown, followed by the derivation and
implementation of the step-size variable least-mean-squares
adaptive noise canceling algorithm[14][15].
In 2017, Jatmiko and Burhanudin made a digital stethoscope
with signal-processing wavelet transformation. This research
has designed and developed a digital stethoscope with
modifications from an ordinary stethoscope that can produce
heart sounds through audio and graphics. The results can be
stored in computer memory with the identification of heart
conditions. The advantages of this research are that the
production is very cheap, portable, produces audio and graphic
data, and can store data and identify the patient's heart condition
83.3%, mitral stenosis with 75% accuracy and the lowest for a
normal heart with 70% accuracy[16]. In (2018) Fardhon
Danang Prakoso has made a tool entitled Electronic
Stethoscope for Wireless-Based Heart and Lung Auscultation
[2][17]. The study reads heart sound signal data using a
computer, so that when operating the device, it still requires a
computer. The weakness of the tool in using a PC is that when
conducting an examination by displaying a heart sound signal,
a PC must be available.
In the Year (2019) Muhammad EH Chowdhury et al has
made real-time digital stethoscope to monitor the heart disease
[18]. The study reads heart sound signal data using a PC, so that
when operating the device, it still requires a PC. The weakness
of the tool in using a PC is that when examining by displaying
a heart sound signal, a PC must be available. In the Year (2019)
Gadang Hendra Prabowo. has made a tool entitled Portable
Electronic Stethoscope. The study displays the signal and BPM
using TFT. The weakness of this tool is that in displaying the
signal it still uses TFT[19][20]. Based on some of the references
above and there are still shortcomings in the development of the
tool, the author will create a device entitled analysis of the
effectiveness of using digital filters in Electronic stethoscopes.
The author wants to develop from the technology side to make
it easier for users so that the examination can be monitored in
real time by displaying signals and BPM values through the
android screen, making diagnosing it easier.
This article has the following structure, in Section 1
(Introduction) which contains the background of the research.
Then Section II (Materials and Method) explains the materials
used in the research, data collection, and procedures used. In
Section III (Result) contains the results and data analysis of the
research that has been done. Section IV (Discussion) contains
sections that need to be discussed regarding the findings in the
research conducted. For Section V (Conclusion) contains the
conclusions of the research that has been done and suggestions
for further research.
II. MATERIALS AND METHODS
This research was conducted as experimental research. The
author intends to conduct further research on the effectiveness of
the use of digital filters to be used in electronic stethoscopes.
Materials and methods will be explained in the following
sections.
Analog Filter
Pre Amplifier
Summing Amplifier
Microcontroller
FIGURE 1. Block diagram of sound signal processing from the heart and
processing of analog and digital filters to display on the LCD Nextion
In the experimental setting, this study used 8 normal people
as respondents. Each respondent will be tapped heart sounds with
several different frequencies. After going through the tapping
process, the signal will be processed with a digital filter and
displayed to the PC display and the signal that has been
converted into a heart sound will be transmitted to a Bluetooth
headset. This study uses a condenser microphone to capture heart
sounds. For voice signal processing digital filters are used. This
study also uses Bluetooth headset that functions to receive heart
signals that have been processed in the form of sound. For this
reason, this research also uses a Bluetooth module. In this study,
after the device was completed, the researchers carried out the
process of tapping heart sounds. Tests carried out at 8
respondents who have gone through the sound recording process.
In the testing process, each respondent will be wired 2 times.
A. DATA COLLECTION
In this study, researchers used a stethoscope with a condenser
mic as the unit tested for measurements on a digital filter. This
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research utilizes heart sound signals as research materials,
Arduino components as microcontrollers. The results are
displayed in the form of a graph on the Nextion TFT LCD.
FIGURE 1 heart sounds will be captured by a stethoscope
through a condenser mic. The condenser mic (on the
stethoscope) converts sound into an electrical signal which will
be amplified through a Pre-Amp circuit with an adjusted gain
value. The output of the Pre-Amp goes into the filter circuit so
that it can filter out the sound frequency needed then the signal
enters the microcontroller to be processed. The signal and value
graphs are then displayed through Nextion in the form of analog
and digital filters.
Start
Initialization
Sound
Detection
Data Processing
Display LCD
Nexian
Finish
FIGURE 2. Flowchart process measurement sound detection until
processing data
FIGURE 2 mic condenser as a source of leads to obtain the
sound of a heartbeat it will produce a voltage. And then it will
be processed and processed by the microcontroller to get the
appropriate signal and will be displayed on the Nextion TFT
LCD.
III. RESULT
In this study, an electric stethoscope was tested to determine the
results of the signal emitted. The following, FIGURE 3 shows
the proposed design of the heart sound detection based on digital
filter.
FIGURE 3. Analog filter Circuit for sound detection and processing circuit for
processing data
Design of electronic stethoscope device module for digital
stethoscope with Nextion display. This tool has undergone the
process of taking data from the circuit using an oscilloscope as
a measuring instrument. The results showed that the analyzer
module of the stethoscope device worked well and could display
graphics on the TFT LCD screen, the condenser mic used was
able to capture heart sound signals clearly.
A. PERFORMANCE MEASUREMENT AND TESTING
RESULTS
This Electronic Stethoscope module is equipped with LPF and
HPF filters to be able to capture human heart signals, so that the
resulting data can not only be seen through the TFT LCD. The
following are the measurement results on HPF and LPF filter
measurements.
FIGURE 4. Measurement of Heart Sound Signal Output After Non Inverting
Amplifier Circuit
FIGURE 4 explains the measurement results on a digital
oscilloscope on the signal output from the condenser mic, the
amplitude obtained is 7.29 Vpp output from the Initial Amplifier
(Pre-Amp) when detecting auscultation of heart sounds which
has the first amplification of 20 times.
FIGURE 5. Measurement of Heart Sound Signal Output After High Pass Filter
with frequency cut off 54 Hz
FIGURE 5 explaining the results of the amplifier output from
the Pre-Amp circuit, the amplitude obtained is 1.92 Vpp the
output signal after passing through the high pass filter circuit is
to pass high frequencies above the cut off frequency according
to the calculation (54.908 Hz) and suppress frequencies below
the cut off.
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TABLE 1
Output Measurement Frequency and amplitude of Heart sound use High Pass
Filter
Frequency
(Hz)
Amplitude
(Vpp)
0
0
20
0,081
40
1,8
60
2,56
80
3,12
100
3,44
120
3,6
140
3,76
160
3,84
180
4,08
200
4,08
The TABLE 1 shows the measurement when it gets input from
the function, with inputs ranging from 0-200 Hz.
FIGURE 6. Measurement of Heart Sound Signal Output After High Pass
Filter with frequency cut off 54 Hz
FIGURE 6 explaining the results of measurements on a digital
oscilloscope on the output signal of the HPF filter circuit, the
amplitude obtained is 1.92 Vpp. The output signal after passing
through the high pass filter circuit is to pass high frequencies
above the cut off frequency according to the calculation, namely
(54.908 Hz) and suppress the frequency at below the cut-off.
TABLE 2
Output Measurement Frequency and amplitude of Heart sound use Low Pass
Filter
Frequency
(Hz)
Amplitude (vpp)
20
4,08
40
3,68
60
3,2
80
2,56
100
2,08
120
1,76
140
1,52
160
1,28
180
1,12
200
0,096
220
0,088
240
0,088
The TABLE 2 shows the measurement when it gets input from
the function, with inputs ranging from 0-200 Hz.
B. MEASUREMENT RESULTS ON RESPONDENT
From the experiments conducted by the author, the results
obtained from the output of the stethoscope and inputted to the
pre-amp where data retrieval through the Deplhi software is then
processed into FFT which functions to find the dominant
frequency of the pcg pre-amp circuit. Where the x-axis
functions as the frequency and the y-axis as the amplitude.
FIGURE 7. Measurement of output Analog Filter Result from Respondent
The FIGURE 7 explain the output on the analog filter before
being inputted into the Arduino program to perform digital filter
signal processing. The output in patient 1 male gets a frequency
of 10.42KHz with an amplitude of 2.92Vpp. In the Data FFT
output digital filter, the author gets the results from the
stethoscope output where data is retrieved through the Ministry
of Environment software then processed into FFT which serves
to find the dominant frequency of the PCG pre-amp circuit.
FIGURE 8. Output measurement of digital filter Result of stethoscope
The FIGURE 8 explain about figure (a) is the result of a male
patient PCG signal graph, the graph above will be input to the
FFT Digital Filter and get the results in Figure 37 (b).
IV. DISCUSSION
For the electric stethoscope concept, a condenser mic that has
been integrated with the stethoscope will intercept heart sounds.
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Later the heart sounds that have been tapped will be processed
with a digital filter. After that, the processed signal will be
displayed on the PC screen. In addition, users can also choose
the signal to be sent. After that the signal will be converted into
heart sounds and sent to the Bluetooth headset. PC displays and
Bluetooth headsets will be monitored directly by the user or the
doctor conducting the examination.
Based on TABLE 1 it can be seen that researchers took data
with several frequencies. The input used is 4.4 volts. It can be
concluded that the data collection on the High Pass Filter circuit
with a cutoff frequency of 20 Hz, the higher the frequency, the
greater the resulting output. Likewise with table 2 of the low
pass filter with a cutoff frequency of 100 Hz, it can be seen that
the lower the frequency, the greater the output. This is because
the High Pass Filter passes signals with frequencies above the
cutoff frequency. while the Low Pass Filter passes signals with
frequencies below the cutoff frequency. The advantage of this
tool is that researchers use condenser mics. The audio signal
produced by a condenser microphone is stronger than that of a
dynamic microphone. Since they tend to be more sensitive and
responsive than dynamic microphones, condenser microphones
are better suited for capturing small details in sound.
Meanwhile, the drawback of this tool is that researchers use a
Bluetooth module to transmit heart sounds to a headset. The use
of Bluetooth has a weakness, namely the data transfer speed is
not fixed and tends to be low. The initial amplifier circuit
module (Pre-Amp) uses the TL084 Op-Amp, where the IC has
4 Op-Amps in it. For the input voltage on this Op-Amp using
+5 and -5 VDC, it is expected that the Op-Amp can work
properly. Reinforcement occurs 20 times. Comparison of the
resistor values above to determine the desired multiplier gain.
The -40dB active filter circuit module requires a passive HPF
filter circuit with 54 Hz Cut Off and an LPF active filter circuit
with 95 Hz Cut off. And we get the first filter circuit in the form
of a -40dB HPF filter and the second filter in the form of a -
40dB LPF filter circuit. The Adder circuit is used to set the
reference signal that is processed by the minimum system. Uses
a variable resistor to adjust the voltage divider[21][21] to the
sound signal that appears on the Nextion screen.
V. CONCLUSION
Overall, this research can be concluded that the addition of a
condenser mic on this tool is very helpful for doctors in
analyzing the patient's condition. When compared to
conventional stethoscopes, stethoscopes. This electric can catch
the sound more clearly. That matter because the author uses a
digital filter with a range of the cut-off frequency is between 20
– 106.15 Hz[13]. Can be seen also on High Pass Filter data table
that the frequency is below the cutoff has a small output as well
as table data Low Pass Filter that the frequency above the cutoff
has an output that is small[22][23][24]. In this study, the
researcher used an input of 4.4 volts[25], Cardiac signals that
are captured and processed by the device This electric
stethoscope is successfully displayed on the PC display and
sending signals to the Bluetooth headset and the user can select
the signal to be transmitted to the Bluetooth headset[27]. The
advantage of this tool is that the heart sound is clearly captured
with the help of a condenser mic so that doctors can more easily
analyze the patient's health condition and make it easier to use
this tool. In this study[28], the tool can produce sound that can
analyze the patient's health condition[29]. Thus this tool can be
used to analyze the condition of the patient's heart
health[30][31].
From the system performance in this circuit[32], when
tapping the condenser mic sensor there is an output signal in the
form of S1 and S2 signals from the heartbeat sound signal with
an indication of lub and dub sounds on the speakers used, the
performance of the circuit is both the Pre-Amp circuit, HPF
Filter and The LPF filter that has been made, the output in the
circuit gets the form of S1 and S2 signals, there is noise caused
by sounds from the surrounding environment[33]. The system
performance on the Nextion display will help monitor the
patient's heart rate signal so that the Nextion display will work
optimally by using the input power supply that has been set at 5
V and the Baud Rate usage on the Nextion of 9600[1].
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