International Journal of Engineering Trends and Technology (IJETT) – Volume 10 Number 6 - Apr 2014
Medical Application of RISC core on single FPGA
Sonal S. Tayade1, S. B. Patil2
Department of Electronics,
Shri Sant Gajanan Maharaj College of Engineering, Maharashtra, India
Abstract— This paper presents the methodology
for monitoring patient using very high speed hardware
description language (VHDL) technique. Patient
monitoring system consist of equipment, devices and
supplies that measure, display and record human
physiological characteristics including heart rate, and
body temperature. A patient monitoring system includes
continuous monitoring of patient including data
acquisition and processing module receiving physiological
data from the patient. The major reason for the
development of this system is to reduce product size,
power consumption and cost of the system. The design has
been implemented in FPGA board and some typical
monitoring and control system has been developed.
Keywords—FPGA, microcontroller, heart rate, body
temperature, beats per minute (bpm).
I. INTRODUCTION
This project aims at making the monitoring system by using
PicoBlaze soft core processor connected the peripheral blocks.
The main objective of this project is to design a system that
continuously check the peripheral readings and control the
system accordingly. The microprocessors used for executing
instructions by fetching from memory. The processor interact
with other peripherals, it requires additional circuitry. This
makes system complexity, requires large area and high power
consumption. We required microprocessor that itself capable
to handle peripherals up to its limit. This feature comes in
PicoBlaze microprocessor. PicoBlaze is a soft core
microprocessor developed by Xilinx that can be synthesized in
some FPGA families. The objective of this work is to design a
non-intrusive, accurate, and low cost biomedical sensor
interface for processing heart rate, and body temperature. The
work deals with the signal conditioning of heart rate, and body
temperature.
A patient monitoring system is an instrument that collects
and displays physiological data, often for the purpose of
watching for, and warning against, very serious changes in
physiological state. Patient monitoring systems can also help
the patient, caregiver, and the provider make more informed
decisions. Care delivery is improved with the use of patient
monitoring systems as the data can trigger alarms or alert
prompting provider intervention with the potential and then to
improve health outcomes.
ISSN: 2231-5381
II. RELATED STUDY
Many works have been conducted to determine the types of
vital signs such as blood pressure, body temperature,
respiration rate that are regularly measured. In our work, we
propose the sensor interface design for only two vital signs
that are heart rate and body temperature.
A. Heart Rate
Heart rate indicates the soundness of our heart and helps
assessing the condition of cardiovascular system [3]. In
clinical environment, heart rate is measured under controlled
conditions like blood measurement, heart voice measurement,
and Electrocardiogram (ECG) [4] but it can be measured in
home environment also [5]. Our heart pounds to pump
oxygen-rich blood to our muscles and to carry cell waste
products away from our muscles. The more we use our
muscles, the harder our heart works to perform these tasksmeans our heart must beat faster to deliver more blood. A
heart rate monitor is simply a device that takes a sample of
heartbeats and computes the Beats per Minute (bpm) so that
the information can easily be used to track heart condition.
There are two types of methods to develop heart monitorselectrical and optical methods. The electrical method has an
average error of 1 percent. The optical method has an
accuracy rating of 15 percent. The average resting human
heart rate is about 70 bpm for adult males and 75 bpm for
adult females. Heart rate varies significantly between
individuals based on fitness, age and genetics. Heart rate can
be measured by measuring one's pulse. Pulse measurement
can be achieved by using specialized medical devices, or by
merely pressing one's fingers against an artery (typically on
the wrist or the neck). It is generally accepted that listening to
heartbeats using a stethoscope, a process known as
auscultation, is a more accurate method to measure the heart
rate. There are many other methods to measure heart rates like
Phonocardiogram (PCG), ECG, blood pressure wave form [6]
and pulse meters [7] but these methods are clinical and
expensive. There are other cost-effective methods that are
implemented with sensors as proposed in [8] and [9] but they
are susceptible to noise and movement of subject and artery.
In this paper, the design and development of a low powered
heart rate monitor device is presented that provides an
accurate reading of the heart rate using optical technology.
The device is economic, durable, and cost effective. We
incorporated the optical technology using standard Light
Emitting Diode (LED) and photo-sensor to measure the heart
rate within seconds using index finger.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 10 Number 6 - Apr 2014
B. Body Temperature
Body temperature means measurement of the body’s ability
to generate and get rid of heat. It is one of chief indicators of
normal functioning and health. The nature of human body is
to keep its temperature within a narrow, safe range in spite of
large variations in temperatures outside the body. The typical
body temperature is 37.0
0.4 (98.6
0.7 ) .When
one is too hot, the blood vessels in his/her skin expand (dilate)
to carry the excess heat to his/her skin’s surface. One may
begin to sweat, and as the sweat evaporates, it helps to cool
his/her body. When one is too cold, his/her blood vessels
narrow (contract) so that blood flow to his/her skin is reduced
to conserve body heat. One may start shivering, which is an
involuntary, rapid contraction of the muscles. This extra
muscle activity helps generate more heat. Under normal
conditions, this keeps one’s body temperature within a narrow,
safe range.
III. EXISTING APPROACHES
There are some existing approaches for monitoring heart
rate. The current technology for measuring heart rate consists
of optical and electrical methods. The electrical method
provides a bulky strap around one’s chest [12]. The optical
method requires no such strap and can be used more
conveniently than the electrical method. Low cost heart rate
measurement device was developed using optical technology.
In optical method, there is an approach using powerful LED
and Light Dependent Register (LDR) to sense pulses [10].
Here, the pulses are amplified by an amplifier circuit and
filtered by a band pass filter. After that the amplified and
filtered pulse signals are sent to the microcontroller. The
microcontroller receives the pulse signals as analog signals
and uses a standard voltage to check if the pulse signals are
valid or not. Then the heart rate is counted by that
microcontroller and displayed the result in a LCD display.
There is also an another approach using infrared Tx and Rx
which also senses pulses, amplifies the pulses and filters
pulses by a low pass filter. Then the pulse signal is sent to a
microcontroller [13, 14]. The microcontroller receives the
pulses as analog signals and checks the signals with a standard
voltage and does the same thing as the above approach. Both
the approach use analog signal to measure heart rate, but
analog signal of pulse varies from person to person. These
approaches cannot calibrate analog signal of pulses for each
person and use a standard voltage to check each pulse signal.
That why these approaches give inaccurate result in many
cases. There is also an approach which uses infrared
technology to measure heart rate and use analog temperature
sensor to measure body temperature. This approach can
calibrate analog signal of pulses for each person. The goal of
our project is to design a remote heart rate and body
temperature monitoring device which is inexpensive, accurate,
durable, and affordable and user friendly using Infrared and
VLSI technology. We have incorporated the infrared
technology using a standard Infrared LED (IR Tx) and photo
diode (Rx) and measured body temperature using LM35. The
ISSN: 2231-5381
IR Tx and Rx have been used to measure the heart rate from
any finger. A microcontroller has been programmed to count
the pulse rate. The body parameter is digitally displayed on a
FPGA display.
IV. INTERFACE DESIGN
Fig 1 Sensor interface block diagram
The above fig 1 shows the block diagram of Low Cost Heart
Rate and Temperature Interface. Fluctuation in the normal
heart rate and body temperature of the patient will be sensed
by the infrared sensor and temperature sensor respectively.
The functioning of heart rate sensor module is based on the
truth that the blood circulates for every heartbeat that can be
sensed by LED. The body temperature will be directly sent to
the microcontroller by the LM 35 temperature sensor.
A. Infrared Transmitter and Receiver
The haemoglobin molecules of blood absorb the infrared
light [10]. Each time heart pumps, the volume of oxygen rich
blood increases in the finger. As a result, the amount of
oxyhaemoglobin molecules also increases in blood.
Absorption of infrared light is also high and, reflection of
infrared light is low. Then, each heart beat slightly alters the
amount of reflected infrared light which can be detected by
the IR Rx. The more infrared light is received the less the
voltage of the input point from the sensor part is produced.
The IR Rx picks an AC signal with some DC components.
The DC components come up from non-pulsatile tissues.
Direct crosstalk between the IR transmitter and receiver is
avoided though they are placed closely. A Resistor is
connected to the Infrared receiver (IR Rx) to reduce the
current drawn by the detection system. If the intensity, of IR
light is too high, then the reflected infrared light from the
tissue will be sufficient enough to saturate the photo detecting
diode all the time, and no signal will exist. So the value of the
resistance connected in series with the Infrared transmitter (IR
Tx) is chosen to limit the current and hence the intensity of the
transmitted infrared light. The diagram in Fig. 2 shows the
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International Journal of Engineering Trends and Technology (IJETT) – Volume 10 Number 6 - Apr 2014
configuration of the IR emitter and IR receiver in relation to
the finger. They are placed in such a way that the infrared
light reflects from the finger to the to the IR receiver [9].
V. ACTUAL HARDWARE TEST RESULT
D. Heart Rate
The microcontroller is programmed to count the number of
B. Filtering and Amplification of Pulse Rate Signal
pulse of the input signal in 15 seconds, and the result is further
multiplied correspondingly by 4 to obtain the total number of
A small movement of finger causes high frequency noise. pulses per minute and convert it into digital form then fed it to
The pulse rate signal filtering is necessary to block any higher FPGA to display the result. It is also programmed to get the
frequency noises present in the signal. The desired signal can analogue signal from the temperature sensor and measure the
be extracted from the noisy signal using a low pass filter. The body temperature ( ).Then the heart rate and the body
equation for cut off frequency of the low pass filter is given temperature are shown on the LCD display which is
below.
connected to FPGA.
Cut off Frequency = 1/2π Rf Cf
(1)
The performance of Heart rate monitor device is tested with
the output of Electrocardiogram (ECG) for 10 patients. The
The cut off frequency of the filter designed is 2.34 Hz. If not error rate is calculated using (1)
amplified, the signal found from the filter circuit is found
having amplitude in mV level. The signal must be amplified
E = [100 |A-M|] A
(1)
for understanding and counting pulse rate by the
microcontroller. A two stage signal filter and amplifier circuit Here
A = Actual heart rate
using LM358 Op Amp can be designed for this. This Op Amp
M=Measured heart rate
is operated with 5 volts. The designed circuit is shown in Fig.
E= Error rate
4. The equation for gain of each stage of the low pass filter is
given below.
The comparison shows that the heart rate monitor device has
accuracy with a mean of 4.31 and standard deviation of 2.87.
Gain of Each Stage = 1 + Rf /Cf
(2)
The comparison is shown in Table I.
In the designed circuit, total gain is 10201. Values of Rf and
Ri are 680 KΏ and 6.8 KΏ. The 1uF capacitors, which are
connected in series to the inputs of each filter blocks the
undesired DC components of the signal. The two 1µF
capacitors must be able to stand some reverse bias, so they
should be nonpolarized.
C. Body Temperature
The LM35 temperature sensor is proposed in this work for
measuring the human body temperature. It is a precision
integrated circuit Temperature Sensor which is small and can
be placed anywhere on the body. The LM35 output voltage is
linearly scalable to the measured temperature, which is 10 mV
per 1 degree Celsius as shown in fig 2. So if Vout = 0.37V
then the measured temperature is 37°C. It does not require
external calibration and maintains an accuracy of ±0.4°C at
room temperature and an accuracy ±0.8°C for a range of 0°C
to +100°C
TABLE I
ACCURACY C OMPARISON WITH AN ECG
Electrocardiogram
ECG (bpm)
76
78
82
83
85
77
79
89
88
76
Heart rate (bpm)
Error Rate (%)
78
78
84
84
90
84
84
96
90
72
2.56
0
2.38
1.19
5.56
8.33
5.95
7.29
2.22
5.56
However, this accuracy may defer depending on the
circumference size of the finger of the user. We also measured
the error rate depending on the finger size and found that
HRM works well with medium-sized fingers. The result is
shown in Table II
TABLE II
ACCURACY COMPARISON WITH DIFFERENT FINGER SIZE
Fig 2 Temperature Sensor Circuit
ISSN: 2231-5381
Finger Circumference
Size
Big Finger(3.0’’)
Error Rate (%)
Medium Finger(2.5’’)
4.31
Small Finger(2.125’’)
8.91
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International Journal of Engineering Trends and Technology (IJETT) – Volume 10 Number 6 - Apr 2014
The accuracy of the heart monitor is also tested manually as
we selected 50 human subjects from different ranges of age
from 3 years to 65 years, and measured their heartbeat
manually from the pulse and with this device. From Fig.2 we
see that the difference between actual heart rate and measured
heart rate is small (e.g., error rate is low).
VI. CONCLUSIONS
We have described the application of RISC core i.e. Pico
Blaze in medical field for the patient Monitoring system. The
results obtained for the body parameter measurement using
VLSI Technique proves better solution over existing patient
monitoring system due to its advantages such as better
accuracy, design security, productivity, speed and flexibility
This work is our ongoing project into the use of embedded
system in the healthcare.
ACKNOWLEDGMENT
The author would like to express thanks and gratitude
to Prof S. B. Patil, SSGMCE, Shegaon (Maharashtra) for
helpful discussions and valuable guidance.
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Fig. 3 Difference between Actual heart rate and measured heart rate
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