2012 7th International Conference on Electrical and Computer Engineering
20-22 December, 2012, Dhaka, Bangladesh
272
Microcontroller Based Health Care Monitoring
System Using Sensor Network
Md. Manirul Islam1,*, Fida Hasan Md. Rafi1,**, Mohiuddin Ahmad1,***, and Abu Farzan Mitul1,****, T. M. N. Tunku
Mansur2, M. A. Rashid2,*****
1
Department of Electrical and Electronic Engineering, Khulna University of Engineering and Technology
Khulna-9203, Bangladesh
2
School of Electrical System Engineering, University Malaysia Perlis, Malaysia
*
mmislameee@gmail.com, **fidaeee@yahoo.com, ***ahmad@eee.kuet.ac.bd, ****mitulnaya@yahoo.com,
*****
abdurrashid@unimap.edu.my
Abstract— Non invasive and continuous measurement of blood
pressure becomes popular now a day. This is very effective way
for hypertensive patients to prevent cardiovascular problems
and precisely regulate anti-hypertension cures. Blood pressure
can be measured by conventional cuff-based sphygmomanometer
or invasive instruments in non continuous mode. In this paper,
we propose the microcontroller based continuous non invasive
cuff less blood pressure measurement system with an alarm
circuit for health care monitoring system. Light signal is used in
sensor network section of this embedded system as light does not
have any harmful effect on human body when it works in
continuous mode. Pulse rate calculation and body temperature
determination is also embedded in this system using sensor
network. Accuracy of the system is found in acceptance range by
comparing the results with the existing conventional systems. If
BP reading, heart rate or body temperature exceeds the standard
range for any patient, the system is able to notify using an
alarming circuit. The whole system is controlled by
microcontroller ATMEGA8L. The overall system is reliable,
accurate, portable, trust worthy, user friendly and cost effective.
Index Terms— non invasive BP, SP, DP, pulse rate, body
temperature, PPG signal, ARS, health care, alarm circuit
I. INTRODUCTION
Health care monitoring system is an important means for
hypertensive patients. Previously many authors worked on this
concept using different methods. Our developed system can
introduce a new approach in healthcare monitoring system by
the use of volume oscillometric method and sensor network
for continuous BP and temperature measurement. Non
invasive continuous BP measurement process can be
organised without calibration means using PWV methods [1].
Although the standard deviation (SD) and mean standard
deviation (MSD) was in acceptable standard value, it can be
further modified with calibration in continuous mode for
higher accuracy.
Instead of using sensor in particular organ, a wearable
health-shirt can be used for 24 hours intensive monitoring
using pulse transit time (PTT) method [2]. However the
variation of the output from standard scale was high enough
and not feasible for critical conditioned patients for 24 hours
monitoring [2]. To achieve the advantage of oscillometry and
vessel buckling method low cuff pressure process for BP
measurement can be used [3]. Since, it was conflicted with
the cuff less requirement for continuous monitoring in noninvasive means.
Accurate beat to beat systolic blood pressure (SP)
calculation using pulse wave transit time (PWTT) method is
useful. It has a singular relation with SP. Diastolic blood
978-1-4673-1436-7/12/$31.00 ©2012 IEEE
pressure (DP) was left outside of study in daily exercise case
[4].
A PTT based BP model and computational algorithm was
used to show dramatic variation of blood pressure in surgical
stimulation. The considered velocity of blood is in a rigid
medium artery [5]. But artery wall expands when blood
volume increases. So volume concept can attain appropriate
result than PTT. New parameter was introduced QdZ for cuff
less non-invasive blood pressure measurement [7]. It is rather
complicated and concerned only SP. Near Infra Red (NIR)
CCD camera was introduced for continuous non-invasive
blood pressure measurement with GPS notification in a
compact system [8]. The overall system was costly and bulky
for portable blood pressure monitoring means.
An algorithm for the estimation of BP from pulse arrival
time (PAT) and heart rate using body sensor network was
proposed in [9]. PPG signal integrated with ECG signal for
continuous non-invasive blood pressure measurement system
is helpful in development of body sensor network [10]. From
only PPG signal BP can be calculated. Nocturnal BP
measurement and monitoring for patient’s during sleep
condition was studied in [11].
In this paper the system shows reliable output for BP, heart
rate and body temperature using cuffless and non-invasive
continuous operating mode with negligible error. This health
care monitoring system works in very efficient way to
calculate blood pressure (BP), body temperature and pulse
rate of a subject. A sensor network consisting of BP sensor
and temperature sensor is used to get PPG signal and body
temperature. It is shown in Fig.1. Output from the sensor is
amplified using double stage amplifier constructed with
LM324 Op-amp with variable gain controller. The amplified
signal is sampled and quantized in ADC and used for the
estimation of BP and heart rate using microcontroller
ATMEGA8L. Calibration set and memory storage block are
used for accurate data analysis and decision making.
Monitoring circuit is also introduced in case of patient’s
critical BP, heart rate and temperature condition.
Temperature sensor
Blood
LED
LDR
Light
Finger
Fig. 1 Position of sensors in the sensor network.
273
The temperature sensor senses patient’s body temperature
change in accordance with the change of patient’s BP and
heart rate. Overall processed numerical data from
microcontroller is displayed in a mini LCD of the system.
This paper is organized as follows: Section II describes the
methodology of BP measurement system. Section III explains
the simulation results as well as calculation of real results and
error. Finally, section IV concludes the entire paper.
II. METHODOLOGY
SP is the degree of force when the heart is pumping
(contracting) and is the maximum blood pressure point.
Similarly the DP is the degree of force when the hearts is
relaxed (expanding) and is the minimum blood pressure point
in Arterial BP curve as shown in Fig. 2.
Arterial blood pressure
140
SP
Pressure (mm Hg)
130
120
microcontroller ATMEGA8L. This microcontroller has 6
channel 10 bit built in ADC. So it makes the overall system a
compact one. A preloaded algorithm processes the data and
estimates BP and pulse rate of the patient. This data is stored
in memory storage for future processing and to compare it
with a predefined standard SP and DP of a patient. If any
patient`s data exceeds the standard value then the alarm circuit
will become activated and will notify patient or the doctor of
the patient’s in such critical condition. A temperature sensor
IC (LM35) is also used along with the arrangement to
determine patient’s body temperature in accordance with the
patient’s BP and heart rate. LM35 can detect temperature
between -55°C to 155°C .This temperature is proportional to
the BP of a patient. So, in hypertension condition patient
sweats a lot. The processed digital data from the
microcontroller attains numerical value and is displayed in a
mini LCD. The mini LCD has 16×2 display section. Only two
lines of results can be displayed. All results can be shown in it
simultaneously.
110
100
Gain
control
MAP
90
DP
80
Heart rate and
BP sensor
70
Sample
and hold
Amplifier
60
0
0.5
1
1.5
2
Time (Second)
2.5
Fig. 2 Typical arterial BP curve for human body.
Mean arterial blood pressure (MAP) can be calculated from
(1).
(1)
MAP = 13 SP + 23 DP
LCD
BP has a proportional relation with density of blood in the
artery or vessel. The work done by the pulse wave can be
expressed in terms of the kinetic energy of the wave and the
gravitational potential energy:
W = F × l = PB A × l = 12 mv 2 + mgh
2
constant ( g = 9.81m / s )and h is height of blood in the
vessel. From (2) PB can be solved.
[
]
Where, V is volume of blood (V=Al) and
blood (
ρ=
m
V
Sample
and hold
Temp.
Sensor
Alarm
circuit
Speaker
Fig. 3 Complete block diagram of health care monitoring system.
The overall system connection for BP measurement and
monitoring is shown in Fig 4. Alarm circuit will be connected
with microcontroller which is not shown in the Fig 4.
5V
10k
1uF
1k
10V
density of
500k 50%
1k
100k
4.7k
7
1k
).Density of blood vessels increases in
accordance with the increase of blood pressure [6].
This health care monitoring system can easily be described
by block diagram as shown in Fig 3. One high bright LED is
placed in one side of the patient’s finger for sensing any
volume change of blood and a detector LDR is placed in
opposite side of the finger to convert the variation of light into
variation of resistance. BP is directly proportional to the
resistance of LDR discussed in our previous paper [6]. The
electrical signal is feed to a double stage amplifier circuit. The
amplifier amplifies the low amplitude bio-signal to high
amplitude one using gain control mechanism for further data
analysis. To suppress dc component from weak bio signal
Automatic reference selector (ARS) is used. Its function was
discussed elaborately in [6]. The highly amplified signal is
sampled. The sampled data is quantized for processing in the
Calibration
setup
ADC
(3)
ρ is
ADC
Microcontroller
(2)
Where, PB is blood pressure (BP), W is work done by pulse
wave, F is force, l is length, A is cross sectional area, m is
mass of blood, v is velocity of blood, g is gravitational
PB = 2mV v2 + Vm gh= ρ 12 v2 + gh
Memory
Storage
Automatic
Reference
selector
26
LM324
4.7k
10k
1
22
21
20
10V
10k 40%
LM324
1uF
14
15
10k
10k
10k
27
28
ATMEGA 8L
10V
500k 50%
5V
5V
25
10k
10V
10V
9
12MHZ
SP control
16
17
18
19
10
500k 50%
Start switch
8
500k 50%
DP control
1k
Gain setting
LCD (16*2)
1
2
5V
3
4
5 6
7
8
9 10 11 12
13 14 15
16
5V
Fig. 4 Complete connection diagram for BP measurement and monitoring.
274
1.00002V
-3.00mV
1.00000V
-3.05mV
0.99998V
LCD2
2.0s 4.0s
V(Vi)
Time
(a) Input weak signal
D7
D5
D4
D3
D2
D6
14
13
12
11
D0
E
D1
9
10
8
7
R
W
RS
5
6
VEE
VDD
5V
U4
14
15
16
17
18
19
9
10
-3.10mV
0s
4
BAT1
3
VSS
LM032L
1
III. RESULT AND CALCULATION
The double stage amplifier circuit from [6] is used here for
extremely high gain mechanism as the detected bio signal is
very low in magnitude even cannot be detected in oscilloscope.
The highly amplified operation of a low magnitude signal
from the amplifier is shown in Fig. 5 and Fig. 6.
The developed device is shown in Fig. 9. After inserting
finger into the sensor module “Do Calibration” instruction is
automatically shown in LCD. In the device three knobs is
used for calibration purpose (SP and DP setup) and gain
control. It is discussed in [6] elaborately. Then it starts to
measure BP continuously.
2
The output of double stage amplifier circuit is connected to
pin 26 of the microcontroller. Pin 27 and 28 are used for DP
and SP control for calibration means (tuning) [6]. A LCD
display is interfaced with the ATMEGA8L.
0s
2.0s 4.0s
V(Vo1)
Time
X1
21
20
PC0/ADC0
PC1/ADC1
PC2/ADC2
PC3/ADC3
PC4/ADC4/SDA
PC5/ADC5/SCL
PC6/RESET
PD0/RXD
PD1/TXD
PD2/INT0
PD3/INT1
PD4/T0/XCK
PD5/T1
PD6/AIN0
PD7/AIN1
AREF
AVCC
23
24
25
26
27
28
1
2
3
4
5
6
11
12
13
U1
1
37.0
ATMEGA8
12MHz
st
PB0/ICP1
PB1/OC1A
PB2/SS/OC1B
PB3/MOSI/OC2
PB4/MISO
PB5/SCK
PB6/TOSC1/XTAL1
PB7/TOSC2/XTAL2
(b) 1 stage output of amplifier
2
VOUT
3
LM35
Fig. 5 Input and 1st stage output wave shape of amplifier.
Fig. 8 Connection diagram of body temperature measurement circuit.
2.65V
2.60V
2.55V
0s
2.0s
4.0s
V(Vo2)
Time
nd
Fig. 6 2 stage output wave shape of amplifier.
(a)
High amplification can be clarified in oscilloscope where
input is in channel 1 in mV range and output is in channel 2 in
in V range. It is shown in Fig 7.
(b)
(c)
Fig. 9 Complete device. (a) Displaying BP, (b) Calibration and gain
setup and (c) Sensor attachment with finger.
Using the device, several data of a patient has been
recorded during his relaxed and after exercise condition.
Pressure (mm Hg)
130
120
SP
110
100
90
80
70
(a)
(b)
60
0
Fig. 7 (a) Weak input signal versus output signal at high gain and (b) Weak
input signal versus clipped output signal due to saturation.
48
72
96
120 144 168 192 216 240 264 288
Time (Sec)
Fig. 10 Measurement of blood pressure at relaxed condition.
135
130
Pressure (mm Hg)
Fig.7 (b) shows that output is clipped due to its saturation
effect which is not desirable. So, a gain control mechanism is
used in the system to prevent saturation effect of the output.
This amplified signal is further processed for BP and pulse
rate calculation as discussed above. The temperature
measurement section is simulated and it is shown in Fig. 8.
In Fig. 8 IC LM35 is used as the temperature sensor. It is
connected with ATMEGA8L to show the body temperature in
LCD. The temperature is accurately measured as shown in Fig.
8. This verifies the proper working of the temperature sensor
in the system.
24
SP
125
DP
120
MAP
115
110
105
100
95
90
0
24
48
72
96
120 144 168 192 216 240 264 288 312
Time (Sec)
Fig. 11 Measurement of blood pressure after exercise.
275
Blood pressure of PPG system (mm Hg)
The SP, DP and MAP of the patients show reasonable
variation in the output for different conditions. The results are
in acceptable standard for practical usage in daily life.
Continuous BP curve of a subject at normal and excited
condition is shown in Fig. 10 and Fig. 11 respectively.
In fig. 12, Red dotted points on the straight line show zero
deviation between cuff based and PPG based system. The
separation between red dotted points and straight line
indicates deviation. So after collecting data of several patients
using the developed device and Sphygmomanometer, it is
plotted in Fig 12. The points are almost in-line with the
standard line which indicates less deviation.
190
REFERENCES
170
[1]
150
130
[2]
110
90
70
[3]
50
50
70
90
110
130
150
170
190
Blood pressure of cuff system (mm Hg)
Fig. 12 Deviation between cuff based and PPG based BP measurement.
For six subjects, SP and DP are measured 3 times for each.
Then MAP is calculated. Standard deviation (SD) of SP, DP
and MAP are calculated and termed as SDSP, SDDP and SDMAP
respectively. These values are shown in Table I.
Sub.
SP
(mm
Hg)
DP
(mm
Hg)
A
120
121
120
128
127
128
130
131
132
126
125
124
135
136
135
145
143
144
82
81
80
84
89
88
85
86
85
82
81
83
87
88
88
92
91
92
C
D
E
F
BP measurement
MAP
SDSP
(mm
(mm
Hg)
Hg)
94.67
94.33
93.33
98.67
101.67
101.33
100
101
100.67
96.67
95.67
96.67
103
104
103.67
109.67
108.33
109.33
[5]
SDDP
(mm
Hg)
SDMAP
(mm
Hg)
[7]
0.47
0.82
0.57
[8]
0.47
2.16
1.34
0.82
0.47
0.42
0.82
0.82
0.47
0.47
0.47
0.42
0.82
0.47
0.57
[9]
[10]
[11]
SD of SP, DP and MAP are very less. Therefore the
developed BP measurement device can easily be used in noninvasively continuous mode in daily life for 24/7 hours BP
monitoring with reliable accuracy.
View publication stats
[4]
[6]
TABLE I
BP MEASUREMENT AND SD CALCULATION
B
IV. CONCLUSIONS
BP measurement using microcontroller based PPG system
for continuous mode is user friendly, flexible and reliable for
patients. We developed the BP measurement device
considering all of these facts and found our results to be
accurate enough for clinical use and all other daily needs.
Implementation of microcontroller and sensor network in the
system has evolved a new approach of health care monitoring
system. Moreover the alarming system notifies cardiovascular
problems at initial stage to the hypertensive patients. The
healthcare monitoring system continuously monitors BP, heart
rate and body temperature with reliable accuracy and alarms
the hypertensive patients about the risk of heart stroke.
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