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Mini project 2013 Heart rate measurement through finger tipCHAPTER 1
INTRODUCTION
This project is based on the principle of photoplethysmography (PPG) which is a non-invasive method of measuring the variation in blood volume in tissues using a light source and a detector. Since the change in blood volume is synchronous to the heart beat, this technique can be used to calculate the heart rate. Transmittance and reflectance are two basic types of photoplethysmography. For the transmittance PPG, a light source is emitted in to the tissue and a light detector is placed in the opposite side of the tissue to measure the resultant light. Because of the limited penetration depth of the light through organ tissue, the transmittance PPG is applicable to a restricted body part, such as the finger or the ear lobe. However, in the reflectance PPG, the light source and the light detector are both placed on the same side of a body part. The light is emitted into the tissue and the reflected light is measured by the detector. As the light doesn’t have to penetrate the body, the reflectance PPG can be applied to any parts of human body. In either case, the detected light reflected from or transmitted through the body part will fluctuate according to the pulsatile blood flow caused by the beating of the heart.
There is a reflectance PPG probe to extract the pulse signal from the fingertip. A subject’s finger is illuminated by an infrared light-emitting diode. More or less light is absorbed, depending on the tissue blood volume. Consequently, the reflected light intensity varies with the pulsing of the blood with heart beat. A plot for this variation against time is referred to be a photoplethysmographic or PPG signal.
The PPG signal has two components, frequently referred to as AC and DC. The AC component is mainly caused by pulsatile changes in arterial blood volume, which is synchronous with the heart beat. So, the AC component can be used as a source of heart rate information. This AC component is superimposed onto a large DC component that relates to the tissues and to the average blood volume. The DC component must be removed to measure the AC waveform with a high signal-to-noise ratio. Since the useful AC signal is only a very small portion of the whole signal, an effective amplification circuit is also required to extract desired information from it.
The use of TCRT100 simplifies the build process of the sensor part of the project as both the infrared light emitter diode and the detector are arranged side by side in a leaded package, thus blocking the surrounding ambient light, which could otherwise affect the sensor performance. The output pulse can be fed to either an ADC channel or a digital input pin of a microcontroller for further processing and retrieving the heart rate in beats per minute (BPM).
Department of ECE 1 Al - Ameen Engineering College
Mini project 2013 Heart rate measurement through finger tip
CHAPTER 2
LITERATURE SURVEY
The Heart rate measurement through fingertip project, the infrared LED and photodiode
used for finger photoplethysmography were actually from salvaged parts, and therefore,
could not provide specifications for them in the article. As a result of that it takes quite a
bit of time to replicate that project with a different set of IR LED and photodiode as the
values of the current limiting and biasing resistors may have to be changed for the new
sensor to work properly. This is a revised version of the same project but with all the
components specified this time. The new version uses the TCRT1000 reflective optical
sensor for photoplethysmography. The use of TCRT100 simplifies the build process of
the sensor part of the project as both the infrared light emitter diode and the detector are
arranged side by side in a leaded package, thus blocking the surrounding ambient light,
which could otherwise affect the sensor performance.
Department of ECE 2 Al - Ameen Engineering College
Mini project 2013 Heart rate measurement through finger tip
CHAPTER 3
BLOCK DIAGRAM
3.1 Amplifier and Counter section
Fig 3.1 Block diagram of Amplifier and Counter section
Department of ECE 3 Al - Ameen Engineering College
Mini project 2013 Heart rate measurement through finger tip3.2 Power Supply
Fig. 3.2 Block diagram of Power supply
Department of ECE 4 Al - Ameen Engineering College
Mini project 2013 Heart rate measurement through finger tipCHAPTER 4
BLOCK DIAGRAM DESCRIPTION
4.1. AMPLIFIER AND COUNTER
The sensor used in this project is TCRT1000, which is a reflective optical
sensor with both the infrared light emitter and phototransistor placed side by side and
are enclosed inside a leaded package so that there is minimum effect of surrounding
visible light. Pulling the enable pin high will turn the IR emitter LED on and activate
the sensor. A fingertip placed over the sensor will act as a reflector of the incident light.
The amount of light reflected back from the fingertip is monitored by the
phototransistor.
The output (VSENSOR) from the sensor is a periodic physiological
waveform attributed to small variations in the reflected IR light which is caused by the
pulsatile tissue blood volume inside the finger. The waveform is, therefore, synchronous
with the heartbeat. The AC signal is amplified by the transistor BC548.
Output of monostable 555 multivibrator remains in its stable state until it
gets a trigger. Primarily the transistor and capacitor are shorted to ground, this state is
considered as the stable state of monostable 555 multivibrator.As we know that, when
the voltage at the second pin of 555 IC goes below 1/3 Vcc, the output becomes high.
The high state is known as ‘Quasi stable’. The trigger causes the transition from stable
state to Quasi stable state. So when we press the button (Trigger), the voltage at 2nd pin
become less than 1/3 Vcc (Disconnected from Vcc), hence the output is high. Then the
discharge transistor is cut off and capacitor starts charging towards Vcc (refer internal
circuit) internal Charging of capacitor is through the resistor R1 with a time constant
R1C1. As the capacitor voltage increases and finally exceeds 2/3 Vcc, it will reset the
internal control flip flop, there by turning off the 555 timer IC. (more than 2/3
Department of ECE 5 Al - Ameen Engineering College
Mini project 2013 Heart rate measurement through finger tip
Department of ECE 6 Al - Ameen Engineering College
Mini project 2013 Heart rate measurement through finger tip
voltage at the threshold pin (6th pin) causes IC to reset).Thus the output goes back to its
stable state from Quasi stable state.
The CD54/74HC190 are asynchronously presettable BCD decade
counters, whereas the CD54/74HC191 and CD54/74HCT191 are asynchronously
presettable binary counters. Presetting the counter to the number on preset data inputs
(A−D) is accomplished by a low asynchronous parallel load (LOAD) input. Counting
occurs when LOAD is high, count enable (CTEN) is low, and the down/up (D/U) input
is either high for down counting or low for up counting. The counter is decremented or
incremented synchronously with the low-to-high transition of the clock. When an
overflow or underflow of the counter occurs, the MAX/MIN output, which is low
during counting, goes high and remains high for one clock cycle. This output can be
used for look-ahead carry in high-speed cascading. The MAX/MIN output also initiates
the ripple clock (RCO) output, which normally is high, goes low, and remains low for
the low-level portion of the clock pulse. These counters can be cascaded using RCO.
The decoder converts BCD input data into control signals. The output form the control
signals for the 7 segment display
Display is the machine man interface in every unit. This section displays
information from the microcontroller. We are planning to use alpha numeric display
since it can display both alphabets and numerals. The display units are incorporated to
perform the machine man interface through which the machine interacts with the user.
The user is first of all advised to enter his / her card in the socket and remove it once the
system read the data. Also other commands to the user are conveyed through this.
Department of ECE 7 Al - Ameen Engineering College
Mini project 2013 Heart rate measurement through finger tip
4.2. POWER SUPPLY
The correct voltage is of almost important for the proper functioning of
IC’s used in the system. Power supply in the circuit is built by using centre tapped full
wave rectifier, filter and regulator. 7812 and 7805 is used for 12V and 5V respectively.
In the receiver with a transformer 230V AC source is stepped for 24V peak to peak. The
down converter is then passed through a bridge rectifier to be converted to 12V DC
supply. Capacitor keeps the voltage to be constant, but as expected, the wave form
contain a lot of ripples. Therefore voltage regulator is needed to correct the imperfection
of the transformer. A 12V 7812 is used to generate 12V and 5V regulator 7805 is used
to generate 5V that is needed. In addition, large capacitors are coupled with the
regulator to offset any ripples or imperfection generated by the transformer.
The rectifier and filter circuit, which are used in the initial stages of a DC
power supply is essential for the operation of almost all electronic devices. A rectifier
circuit is a circuit which convert AC voltage to pulsating DC. There are 2 type of
rectifier circuit are half wave rectifier and full Wave rectifier
Now in the case of full wave rectifier circuit, this allows a unidirectional
current to flow through the load during the entire input cycle. As a result of this, output
voltage that pulsates every half cycle of the input.
A transformer is static piece of apparatus by means of which electric
power in 1 circuit is transformed in to electrical power of the same frequency in another
circuit. It can raise or lower the voltage in a circuit but with corresponding decrease or
increase in current
Department of ECE 8 Al - Ameen Engineering College
Mini project 2013 Heart rate measurement through finger tip
CHAPTER 5
CIRCUIT DIAGRAM
5.1 SENSOR AND AMPLIFIER
Fig: 5.1 Circuit diagram of Sensor and Amplifier
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Mini project 2013 Heart rate measurement through finger tip
5.2 COUNTER AND DISPLAY
Fig : 5.2 Circuit diagram of Counter and Display
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Mini project 2013 Heart rate measurement through finger tip
5.3 POWER SUPPLY
Fig: 5.3 Circuit diagram of Power Supply
Department of ECE 11 Al - Ameen Engineering College
Mini project 2013 Heart rate measurement through finger tip
CHAPTER 6
CIRCUIT DIAGRAM DESCRIPTION
6.1 Amplifier and Counter section
The sensor used in this project is TCRT1000, which is a reflective optical
sensor with both the infrared light emitter and phototransistor placed side by side and
are enclosed inside a leaded package so that there is minimum effect of surrounding
visible light. The circuit diagram below shows the external biasing circuit for the
TCRT1000 sensor. Pulling the enable pin high will turn the IR emitter LED on and
activate the sensor. A fingertip placed over the sensor will act as a reflector of the
incident light. The amount of light reflected back from the fingertip is monitored by the
phototransistor.TCRT1000 used for sensing pulse from fingertip
Department of ECE 12 Al - Ameen Engineering College
Mini project 2013 Heart rate measurement through finger tip
Fig 6.1: Sensor circuit
The output (VSENSOR) from the sensor is a periodic physiological
waveform attributed to small variations in the reflected IR light which is caused by the
pulsatile tissue blood volume inside the finger. The waveform is, therefore, synchronous
with the heartbeat. The following circuit diagram describes the first stage of the signal
conditioning which will suppress the large DC component and boost the weak pulsatile
AC component, which carries the required information. The AC signal is amplified by
the transistor BC548.
Department of ECE 13 Al - Ameen Engineering College
Mini project 2013 Heart rate measurement through finger tip
Fig 6.2: BC548
6.1.1 Monostable Multivibrator
Output of monostable 555 multivibrator remains in its stable state until it
gets a trigger. Primarily the transistor and capacitor are shorted to ground, this state is
considered as the stable state of monostable 555 multivibrator. As we know that, when
the voltage at the second pin of 555 IC goes below 1/3 Vcc, the output becomes high.
The high state is known as ‘Quasi stable’. The trigger causes the transition from stable
state to Quasi stable state. So when we press the button (Trigger), the voltage at 2nd pin
become less than 1/3 Vcc (Disconnected from Vcc), hence the output is high. Then the
discharge transistor is cut off and capacitor starts charging towards Vcc (refer internal
circuit) internal Charging of capacitor is through the resistor R1 with a time constant
R1C1. As the capacitor voltage increases and finally exceeds 2/3 Vcc, it will reset the
internal control flip flop, there by turning off the 555 timer IC. (more than 2/3 voltage at
Department of ECE 14 Al - Ameen Engineering College
Mini project 2013 Heart rate measurement through finger tipthe threshold pin (6th pin) causes IC to reset).Thus the output goes back to its stable
state from Quasi stable state.
Design equation for monostable multivibrator
On time, T=1.1 R1 C1 For time period : 30 seconds
Assuming C=470µF, we get R=56kΩ
For time period: 20 seconds
Assuming C=470µF, we get R=39kΩ
For time period: 3 minutes
Assuming C=470µF, we get R=330Kω
6.1.2 555 Timer IC Working Principle
Comparator 1 has a threshold input (pin 6) and a control input (pin 5). In
most applications, the control input is not used, so that the control voltage equals +2/3
VCC. Output of this comparator is applied to set (S) input of the flip-flop. Whenever the
threshold voltage exceeds the control voltage, comparator 1 will set the flip-flop and its
output is high. A high output from the flip-flop saturates the discharge transistor and
discharge the capacitor connected externally to pin 7. The complementary signal out of
the flip-flop goes to pin 3, the output. The output available at pin 3 is low . These
conditions will prevail until comparator 2 triggers the flip-flop. Even if the voltage at
the threshold input falls below 2/3 VCC, that is comparator 1 cannot cause the flip-flop to
change again. It means that the comparator 1 can only force the flip-flop’s output
high.To change the output of flip-flop to low, the voltage at the trigger input must fall
below + 1/3 Vcc. When this occurs, comparator 2 triggers the flip-flop, forcing its
output low. The low output from the flip-flop turns the discharge transistor off and
forces the power amplifier to output a high. These conditions will continue independent
of the voltage on the trigger input. Comparator 2 can only cause the flip-flop to output
low.
Department of ECE 15 Al - Ameen Engineering College
Mini project 2013 Heart rate measurement through finger tip
Fig no: 6.3 Internal diagram of 555 Timer IC
6.1.3 555 timer
From the above discussion it is concluded that for the having low output
from the timer 555, the voltage on the threshold input must exceed the control voltage
or + 2/3 VCC. They also turn the discharge transistor on. To force the output from the
timer high, the voltage on the trigger input must drop below +1/3 VCC. This also turns
the discharge transistor off.
A voltage may be applied to the control input to change the levels at
which the switching occurs. When not in use, a 0.01 nanoFarad capacitor should be
connected between pin 5 and ground to prevent noise coupled onto this pin from
causing false triggering.
Connecting the reset (pin 4) to a logic low will place a high on the output
of flip-flop. The discharge transistor will go on and the power amplifier will output a
low. This condition will continue until reset is taken high. This allows synchronization
or resetting of the circuit’s operation. When not in use, reset should be tied to +VCC.
Department of ECE 16 Al - Ameen Engineering College
Mini project 2013 Heart rate measurement through finger tip6.1.4 Counter and Display
The CD54/74HC190 are asynchronously presettable BCD decade
counters, whereas the CD54/74HC191 and CD54/74HCT191 are asynchronously
presettable binary counters. Presetting the counter to the number on preset data inputs
(A−D) is accomplished by a low asynchronous parallel load (LOAD) input. Counting
occurs when LOAD is high, count enable (CTEN) is low, and the down/up (D/U) input
is either high for down counting or low for up counting. The counter is decremented or
incremented synchronously with the low-to-high transition of the clock. When an
overflow or underflow of the counter occurs, the MAX/MIN output, which is low
during counting, goes high and remains high for one clock cycle. This output can be
used for look-ahead carry in high-speed cascading. The MAX/MIN output also initiates
the ripple clock (RCO) output, which normally is high, goes low, and remains low for
the low-level portion of the clock pulse. These counters can be cascaded using RCO.
The decoder converts BCD input data into control signals. The output
form the control signals for the 7 segment display
.
6.2 Power Supply
The system requires a regulated +5v supply for the semiconductors and
circuit. These can be delivered from the 230V domestic supply. Before applying this to
the system we must step down this high voltage to an appropriate value. After that it
should be rectified. This will provide a unidirectional current. To achieve a +5V DC we
should regulate this. All these are done in the power supply circuitry, which is explained
below. Full-wave rectification converts both polarities of the input waveform to DC,
and is more efficient. However, in a circuit with a non-center tapped transformer, four
rectifiers are required instead of the one needed for half-wave rectification. This is due
to each output polarity requiring two rectifiers each, for example, one for when AC
terminal 'X' is positive and one for when AC terminal 'Y' is positive. The other DC
Department of ECE 17 Al - Ameen Engineering College
Mini project 2013 Heart rate measurement through finger tipoutput requires exactly the same, resulting in four individual junctions (See
semiconductors/diode). Four rectifiers arranged this way are called a bridge rectifier:
A full wave rectifier converts the whole of the input waveform to one of
constant polarity (positive or negative) at its output by reversing the negative (or
positive) portions of the alternating current waveform. The positive (negative) portions
thus combine with the reversed negative (positive) portions to produce an entirely
positive (negative) voltage/current waveform
Fig 6.4 Center tapped rectifier
6.2.1 Rectifier output smoothing
While half- and full-wave rectification suffices to deliver a form of DC
output, neither produces constant voltage DC. In order to produce steady DC from a
rectified AC supply, a smoothing circuit, sometimes called a filter, is required. In its
simplest form this can be what is known as a reservoir capacitor, Filter capacitor or
smoothing capacitor, placed at the DC output of the rectifier. There will still remain an
amount of AC ripple voltage where the voltage is not completely smoothed. Sizing of
the capacitor represents a tradeoff. For a given load, a larger capacitor will reduce ripple
but will cost more and will create higher peak currents in the transformer secondary and
Department of ECE 18 Al - Ameen Engineering College
Mini project 2013 Heart rate measurement through finger tipin the supply feeding it. In extreme cases where many rectifiers are loaded onto a power
distribution circuit, it may prove difficult for the power distribution authority to
maintain a correctly shaped sinusoidal voltage curve.
For a given tolerable ripple the required capacitor size is proportional to
the load current and inversely proportional to the supply frequency and the number of
output peaks of the rectifier per input cycle. The load current and the supply frequency
are generally outside the control of the designer of the rectifier system but the number
of peaks per input cycle can be effected by the choice of rectifier design.
A half wave rectifier will only give one peak per cycle and for this and
other reasons is only used in very small power supplies. A full wave rectifier achieves
two peaks per cycle and this is the best that can be done with single phase input. For
three phase inputs a three phase bridge will give six peaks per cycle and even higher
numbers of peaks can be achieved by using transformer networks placed before the
rectifier to convert to a higher phase order. To further reduce this ripple, a capacitor-
input filter can be used.
This complements the reservoir capacitor with a choke and a second filter
capacitor, so that a steadier DC output can be obtained across the terminals of the filter
capacitor. The choke presents a high impedance to the ripple current. If the DC load is
very demanding of a smooth supply voltage, a voltage regulator will be used either
instead of or in addition to the capacitor-input filter, both to remove the last of the ripple
and to deal with variations in supply and load characteristics.
6.2.2 3 terminal voltage regulator for ± 5 v
The L7800 series of three-terminal positive regulators is available in TO-
220 ISOWATT220 TO-3 and D2PAK packages and several fixed output voltages,
making it useful in a wide range of applications. These regulators can provide local on-
card regulation, eliminating the distribution problems associated with single point
regulation. Each type employs internal current limiting, thermal shut-down and safe
area protection, making it essentially indestructible. If adequate heat sinking is
Department of ECE 19 Al - Ameen Engineering College
Mini project 2013 Heart rate measurement through finger tipprovided, they can deliver over 1A output current. Although designed primarily as fixed
voltage regulators, these devices can be used with external components to obtain
adjustable voltages and currents.
Fig no: 6.5 Voltage regulator
Three-terminal IC power regulators include on-chip overload protection
against virtually any normal fault condition. Current limiting protects against short
circuits fusing the aluminum interconnects on the chip. Safe-area protection decreases
the available output current at high input voltages to insure that the internal power
transistor operates within its safe area.
Finally, thermal overload protection turns off the regulator at chip
temperatures of about 170°C, preventing destruction due to excessive heating. Even
though the IC is fully protected against normal overloads, careful design must be used
to insure reliable operation in the system.
FEATURES
1. Output current up to 1.5 A
2. Output voltages of 5; 5.2; 6; 8; 8.5; 9;12; 15; 18; 24V
3. Thermal overload protection
Department of ECE 20 Al - Ameen Engineering College
Mini project 2013 Heart rate measurement through finger tip4. Short circuit protection
5. Output transition safe operating area protection
R11KU1
L7805/TO220
1
3
2VIN
GND
VOUT
C3CAP NP
D2
LED
GND
+C12200MFD
230V
D1
1n4007
1 2
+12V VCC
230V
+ C210MFD
T1
12 - 0-12V / 1AD3
1n4007
1 2
Fig 6.2.3 5V Power supply
This ac supply goes to a center tap rectifier, which converts the ac into a
unidirectional voltage. The ripples in the resulting supply is filtered and smoothed by a
2200FD/25V capacitor. The 0.1F capacitor bypasses any high frequency noises. The
resulting supply has the magnitude above 17V. This voltage is fed to the regulator IC
7805. This IC provides a regulated 5V positive supply at its 3rd pin. The required input
for this is more than 7.5V. Also there is an LED in series with a 1K resistor. This
will act as a power ON indicator.
Department of ECE 21 Al - Ameen Engineering College
Mini project 2013 Heart rate measurement through finger tip
CHAPTER 7
ADVANTAGES
7.1 ADVANTAGES
The patient’s heart beat rate is monitored using a photoelectric sensor
which can sense the patients’s pulse rate.
This method of tracking the heart rate is more efficient than traditional
method By derives the same from the ECG graph.
The duty nurse or doctors can easily identify the problems. This saves
the life of the patient.
By using the system, labor work can be reduced i.e., there’s no need to
go and check the patients consistently.
It provides increased accuracy in identifying the breathing rhythm.
Department of ECE 22 Al - Ameen Engineering College
Mini project 2013 Heart rate measurement through finger tip
CHAPTER 8
FUTURE SCOPE
The information updated through these devices sent to a doctor or
medical adviser for checking the health status of the person. The device is of great
application since we are in a world of less time and space. All basic diagnosis involve
heartbeat. It provide a cost effective method to improve chronic disaster management. A
graphical LCD can be used to display a graph of the change of heart rate over time.
Sound can be added to the device so that a sound is output each time a pulse is received.
The maximum and minimum heart rates over a period of time can be displayed.Serial
output can be attached to the device so that the heart rates can be sent to a pc for further
online or offline analysis.
Department of ECE 23 Al - Ameen Engineering College
Mini project 2013 Heart rate measurement through finger tip
CHAPTER 9
CONCLUSION
A remote patient monitoring system was developed to facilitate patient
empowerment and also to provide accurate and timely data to the care provider to help
with disease management. This system has been evaluated in populations with
hypertension. It provides a cost effective method to improve chronic disease
management. Controlling a parameter such as blood pressure in complications such as
renal and cardiovascular disease can result in improved health outcomes and increased
quality of life. Acquiring biological signal and adequately amplifying biological signal.
Semi functional heart rate counter and use of low power components for battery
operation
Department of ECE 24 Al - Ameen Engineering College
Mini project 2013 Heart rate measurement through finger tip
REFERENCES
[1] Dr. A.K. GAUTAM “Antenna and Wave propagation” S.K Kataria &
Sons Publishers, Fourth Edition 2008 – 09.
[2] Dr.S.K. Sahwaney ”Electronics Measurement and instrument.
[3] Robert L. Boylestad “Electronics Device and Circuit Theory by “
[4] Communication System by: B.P. Lathi.
[5] S. Edwards., “Heart rate Monitor Book”, Leisure systems international,
Dec.1993.
[6] M. Malik and A. J. Camm., “Heart Rate Variability”., Futura Publishing
Co. Inc., sept. 1995.
[7] J. R. Hampton., “The ECG In Practice”., Churchill Livingstone., Mar. 2003.
[8] A. R. Houghton and D. Gray., “making sense of the ECG”., Hodder
Arnold Publishing.m 2003.
[9] Microchip
Web site: http://microchip.com
[10] American Heart Association. “Cardiovascular Disease Statistics”
[Online Document], 2008 [Cited 9 Dec 2008], Available HTTP:
<http://www.americanheart.org/presenter.jhtml?identifier=447
Department of ECE 25 Al - Ameen Engineering College
Mini project 2013 Heart rate measurement through finger tip [11] Centers for Disease Control and Prevention. “Heart Disease Facts and
Statistics” [Online Document], 10 Sept 2008 [Cited 4 Dec 2008], Available
HTTP: < http://www.cdc.gov/heartdisease/statistics.htm>.
[12] R.S. Khandpur. Biomedical Instrumentation: Technology
and Applications, McGraw-Hill Companies, Inc., 2005.
[13] V. Virgilio. “Prototype of a Portable ECG Monitoring System
(Holter Monitor) with Real Time Detection of Beat Abnormalitie”
Master thesis, Aalborg University, 2006.
[14] J. Hailong, M. Bing. “Design of Holter ECG System Based on
MSP430 and USB Technology” IEEE (2007) 976-979.
[15] The Electricity and the Heart website. Available
from :http://www.naspe.org/library/electricity_and_the_heart.
[16] Electronics for you website.
[17] Embedded lab website. Available
from: http://www.IntroducingEasy Pulse A DIY
photoplethysmographic sensor for measuring heart rate
Embedded Lab.htm.
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Mini project 2013 Heart rate measurement through finger tip
APPENDIX
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Mini project 2013 Heart rate measurement through finger tip
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