An Improved Signal Conditioning system for
wireless health monitor
T.Meenalochini
P.Manimehalai
S.Ravindrakumar
Department Of ECE
Chettinad College of Engineering
and technology
Karur, India
Department Of ECE
Chettinad College of Engineering
and Technology
Karur, India
Department Of ECE
Chettinad College of Engineering
and Technology
Karur, India
meenalochini93@mail.com
manimehalai58@gmail.com
Abstract --- The aim of this paper is to develop a small wireless
sensor system that records ECG signal and sends to a PDA via a
Bluetooth module. The Electrocardiogram (ECG) is an essential
diagnostic tool that measure and record the electrical activity of
the heart. A wide range of heart conditions can be detected while
interpreting the recorded ECG signals. These qualities make
ECG a perfect instrument for patient monitoring and
supervision. The commonly used ECG-machine used for
diagnosis and supervision at the present is expensive and
stationary. This paper makes the patient mobile, contributing to
the cable reduction in medical and physiotherapy environments.
ECG sensor system prototype is to be developed. Using
Bluetooth™ technology the ECG sensor system can connect to a
personal digital assistant (PDA) which graphically presents the
ECG-signals. Software for the PDA is developed for presentation
of the 2-channel ECG-sensor. With the use of a microcontroller
the analog signal is digitally converted at a specific sample rate
based on the resolution of the ECG signals. The prototype is well
suited for patient monitoring with a low noise and a power
efficient system, powered by a cellular phone battery.
Keywords: ECG, Bluetooth, PDA
I. Introduction
The electrocardiogram (ECG) is one of the most relatively
inexpensive and easily accessible investigational tools for the rapid
diagnosis of arrhythmias. The ECG is graphical record of direction
and magnitude of the electrical activity that is generated by
depolarisation of atria and ventricles. In fact, beat detection is
necessary to determine the heart rate and several related arrhythmias
such as Tachycardia, Bradycardia and Heart Rate Variation. It is also
necessary for further processing of the signal in order to detect
abnormal beats [3]. Our idea is to use an instrumentation amplifier
along with state variable and fleige filter, notch filter to be cascaded
for removing DC offset. We have designed the circuit for the same.
The significant advantage of this paper is its ability for accessing
vital bio-signals of several patients and makes such monitoring
convenient.
A.ECG Waveform
A typical waveform from an electrocardiogram (ECG) is
shown in fig.1. It consists of several complexes, the P-complex, the
RS-complex, the T complex and the U-complex.Fig.1- Typical wave
gsravindrakumar7@gmail.com
form of an ECG. The dominant component of the ECG is the QRS
complex, which indicates the electrical depolarization of the muscles
in the ventricle of the heart. [1] Several clinical applications
including ECG monitoring system in intensive care unit, operating
room and implantable defibrillator require accurate QRS detection
algorithms whiles the QRS is easily recognized by a human observer.
Fig. 1 ECG Waveform
1) Artefacts
The ECG waveform contains, in addition to the QRS
complex, P and T waves, 60-Hz noise from power line interference,
EMG from muscles, motion artefact from the electrode and skin
interface, and possibly other interference from electro-surgery
equipment in the operating room. Many clinical instruments such as
a cardio-tachometer and an arrhythmia monitor require accurate realtime QRS detection. It is necessary to extract the signal of interest,
the QRS complex, from the other noise sources such as the P and T
waves. The motion artefacts, EEG signals and muscle noise are also
accompanied in ECG where they are been major cause for error in
ECG measurement [2].
2) ECG Signals
Each wave in ECG presents recharge and discharge of a
certain region of heart [3]. This helps in indicating which area of the
heart is affected. Also, the size of each wave corresponds to the
amount of voltage generated by that region or the event creating it. In
a standard ECG recording there are five electrodes connected to the
patient namely right arm,left arm, left leg, right leg and chest.
Each pair contains unique information of the heart activity that
cannot be obtained from another pair of leads. The different leads are
divided into groups depending how they are connected to the ECG
amplifier [1].
B. Lead I
the R wave, and finally squared to further exploit the highfrequency content of the QRS complex. The ECG signals
considered at this point are measured as discrete-time signals
by an analog-to-digital converter (ADC) performing
quantization with a resolution of 12 bits at a sampling
frequency of 200 Hz. Power-of-two coefficients filters lead to
design constraints that make it difficult to achieve sharp cutoffs. Equation (1) defines the transfer function for the digital
band-pass filter.
Fig. 2 Einthoven triangle
The main signal measured from Lead I is by
measuring the electrical potential between left arm and right
arm. The left arm is the positive pole; an electrical wave
moving towards the left arm will cause an upward deflection
of electrocardiograph. Lead I has angle that is 0º relative to
the heart therefore it is most useful for detecting electrical
activity in a horizontal direction. Einthoven’s triangle is an
equilateral triangle with the heart at the centre. The difference
in the potential between L1 (connected to left arm) and L2
(connected to right arm) is used to produce a wave of an ECG
trace. The L3 connected to the left leg of body is common
grounded [3].
II. Literature Survey
A. Qrs Detection
2) Filter Properties
Since band pass filters can operate at higher speeds than
traditional designs, they are often the best type of filter when
using slow general-purpose microcontrollers. These filters
also minimize the round-off and truncation errors. Amplitude
response of the digital band pass filter by using bit-shifting
and add-subtract instructions instead of floating-point
multiplication instructions which makes the resulting
programs less burdensome to implement [10].
3) Drawback
There is noise interruption which can be overcome by
advanced function such as digital noise rejection filter. It is
not reliable. There would be an alarm circuit to alert in case of
emergency.
B. Total Heart Care Unit
Fig. 3 Filtering of ECG signals
The detector is based on the Hamilton- Tompkins backward
difference algorithm [7]. The detection algorithm uses a band
pass filter and a squaring stage to improve the signal-to-noise
ratio for an adaptive threshold decision stage. The
performance of the presented detector was tested with
artificially generated signals, and with records from the MITBIH arrhythmia database. The QRS detector is divided into
two stages, (1) the pre-processor stage and (2) the decision
stage. The first stage enhances the QRS complex by reducing
the contribution of the non-correlated noise. The second stage
detects the enhanced QRS occurrences based on an adaptive
threshold algorithm [5].
The easy-to-use Total Heart Care Unit device helps
monitoring patients at risk of suffering a heart attack and takes
the appropriate action to detect and overcome the potential
problem. It acts as a permanent wireless communication link
to the doctor and assists patients in making healthy life-style
decisions. It is intended as a portable device that an individual
can wear constantly, with data sent to a central server for
storage or further analysis as needed
1) Working
The ECG signal is first band pass filtered to suppress noise
and artefacts, then differentiated to highlight the large slope of
Fig 4 Total Heart Care Unit
1) ECG Sensor And Monitoring Circuit Design
The design is based on the converter-per-channel
monitoring circuit used in many ECG devices. This design amplifies,
filters, and digitizes each analog channel independently, resulting in
superior throughput speed and the ability to further process. Each
channel using features built into the analog to digital converter
(ADC).
Fig. 5 MONITORING CIRCUIT
The hardware component of the Total Heart Care
Unit consists of a sensor circuit, which filters the measured
heart wave, and a data acquisition unit, which interfaces with
the analysis program by converting the signal into digital form
and sending the information to the computer through the
serial port.
2) Disadvantage
Though it is found easier in wireless application, it is
found that the working took much time for table replacement.
It could cover only a distance of 10m radius. There is no fast
transmission of data and there occurs a delay but the time is
mandatory for emergency monitoring. The power consumed is
very large. It does not offer NFC (Near Field Communication)
support.
III. Proposed Work
Fig.6 Block Diagram
ionic current generated from electrochemical activity into the
electronic current of measurement system. Nowadays, EIT
(electricity Impedance technology) becomes one of the
research hot spots in the field of Biomedical Engineering [4, 5
and 8]. The skin must be rubbed with a mild abrasive to
remove the thin layer of dead skin to enable better ion flow
between the tissues. Electrolyte on the electrode Dry and/or
old skin creates a high impedance, which makes it difficult to
acquire good readings. In addition, electrode to skin
impedances varies due to ethnicity, age, and gender. Skin to
electrode impedances at 10 Hz using silver/silver chloride
electrodes, with the skin properly prepared, are typically about
5 kΩ. When designing ECGs and other bio-potential front-end
circuits, the designer must remember that an impedance of
500 kΩ can be encountered frequently.
1) Ag/AgCl Electrode
A very popular electrode is silver/silver chloride
(Ag/AgCl) because of its very low half-cell potential of
approximately 220 mV and its ease of manufacturability.
Ag/AgCl electrodes are low noise and low polarization
electrodes [5], they allow current to pass across the interface
between the electrolyte and the electrode. Non-polarized
electrodes are better than polarized electrodes in terms of their
rejection of motion artefacts and their response to
defibrillation currents. Both motion artefacts and defibrillation
events can charge up the capacitance from the electrolyte and
electrode interface. The AgCl layer lowers the impedance of
the electrode. This is important at low frequencies near dc,
where ECG measurement is taken. The voltage is in the range
of 1 mV ~ 5 mV.
B. Signal Conditioning
A. ECG Electrodes
Bio-electricity, a basic physiological phenomenon, can
always be measured using the biomedical electrodes.
Biomedical electrodes are a kind of biosensors that transforms
1) Instrumentation Amplifier
Many industrial and medical applications use
instrumentation amplifiers (INAs) to condition small signals
in the presence of large common-mode voltages and DC
potentials. Standard INAs using a unity gain difference
amplifier in the output stage, however, can limit the input
common mode range significantly. Thus, common mode
signals induced by adjacent equipment, as well as large
differential DC potentials from differently located signal
sources, can increase the input voltage of the INA, causing its
input stage to saturate. Saturation causes the INA output
voltage, although of wrong value, to appear normal to the
following processing circuitry. This could lead to disastrous
effects with unpredictable consequences. This paper reviews
some principles of the classic three-op-amp INA and provides
design hints that extend the input common mode range to
avoid saturation while preserving overall gain at maximum
value. The paper also discusses the removal of large
differential DC voltages through active filtering; avoiding
passive RC filters at the INA input that otherwise would lower
its common-mode rejection ratio (CMRR).
The amplifier in this paper is a standard single supply
instrumental amplifier with an additional variable gain and a
passive low pass filter of the first degree and a DC restoration
loop for elimination of possible DC offset in the circuitry.
has a power consumption of 2.3 mA that is approximate 0.5
mA lower than when using 10 MHz crystal. When the
Bluetooth™ module programs as spp_Slave the complete
circuitry has a power consumption of 60 mA when connected
in a piconet or PAN.
E. Mikro C (Microcontroller)
A C compiler, MikroC is used to create the program for
Pic18f452. MikroC creates a .hex-file that can be downloaded
into the microcontroller using MPLAB IDE 7.30 and
PICSTART Plus. The inbuilt ADC returns a 10 bit value, by
shifting the two least significant an 8 bit value that is left, can
be sent as one byte via the virtual serial port that is emulated
by the Bluetooth Module Spp_slave profile. Requirements for
the microcontroller program:
 Sample rate: 400 Hz
 Crystal: 4 MHz
 Number of channels: 2
 Bits per Byte: 8
 Baud rate: 19200 baud/s
 Stop bit: 1
2) Cascaded Filters
A state variable filter is a type of active filter. It
consists of one or more integrators, connected in some
feedback configuration. Any LTI system can be described as a
state-space model, with n state variables for an nth-order
system. A state variable filter realizes the state-space model
directly. The instantaneous output voltage of one of the
integrators corresponds to one of the state-space model's state
variables. Fliege filter, type of an active filter works as a band
pass filter. It allows huge range of ECG waves to pass through
it. It is cascaded next to the state variable filter for better
accuracy. A notch filter (band stop) having highest frequency
attenuation 10 to 100 times the attenuation of the lowest
frequency will be at final stage. It is independent of the Q
value.
F. Bluetooth Module
It supports the Serial Port Profile for the
communication between the ECG amplifier and the handheld
PDA [11].It supports distance of 100 m radius. Power
consumption is expected to be very less. BlueLab27 is used
for programming the Bluetooth® Module with the serial port
profile profile slave (spp_slave) to enable the PDA to locate
and exchange link key with the ECG-amplifier. Bluetooth
technology operates at 2.4 to 2.485 GHz ISM, industrial,
scientific and medical band. The 2.4 GHz ISM band is
available and unlicensed.in most countries [12].It uses PSK
modulation.
G. Advantages Of The Proposed Paper
C. Right Leg Drive Circuit
The function of the Right Leg Drive (RLD) is to
eliminate the common mode noise generate from the body.
The two signals that are entering the differential amplifier
from the leads placed on the right and left arm according to
Einthoven’s triangle are summed, inverted and amplified back
into the body though the right leg by a common-mode
amplifier. This signal is fed back to the other leads and
eliminates the noise signal drowning the wanted ECG signals.
D. Microcontroller
The microcontroller pic18f452 is used as ADC as
well as universal asynchronous receiver-transmitter, UART,
for a serial connection to the Mitsumi Bluetooth™ Module.
The microcontroller also controls the sample frequency which
must be set to 400Hz for both signals. The Microcontroller
It could support NFC covering larger distance. The
data is expected to transmit and the delay is expected to be
comparatively lesser from our previous literature survey. The
power consumption is very lower. It is believed to offer
greater security.
FUTURE WORK
Other advanced function such as digital noise
rejection filter or FFT analysis can be implemented in the
LabView application depending on hardware of the PDA.
CONCLUSION
We have designed filtering circuits on our own. We
have described our idea in this paper which has advanced
technology when comparing to the literature survey.
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