Design and Implementation of Heart Rate Measurement Device UsingWireless System

Md. Rifat Hazari, Effat Jahan Department of Electrical and Electronic Engineering

American International University-Bangladesh (AIUB) Dhaka, Bangladesh

E-mail: rifat.hazari@gmail.com, effat.jahan25@gmail.com

Md. Rashedul Amin, Md. Ashraful Alam Department of Electrical and Electronic Engineering

American International University- Bangladesh (AIUB) Dhaka, Bangladesh

E-mail: md.rashedul.amin@gmail.com, ashrafuleee@ymail.com

Abstract—Nowadays, the biomedical instrumentation holds a prominent position within medicine. Following this trend, the BPM (beat per minute) has become an important tool to elucidate about the functioning of the organism and wakeup for anomalies by monitoring the heartbeat in the human body. These devices are mostly used in hospitals and clinics but are gradually finding their way into domestic use. This paper demonstrates on an approach to design a cheap, accurate and reliable device which can easily measure the heart rate of a human body.

Keywords-Finger tip sensor; Microcontroller; MCP 604; Opamp,RF module, PCB.

I. INTRODUCTION Heart rate is the number of heartbeats per unit of time, typically expressed as beats per minute (bpm). Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes during exercise or sleep [1].The measurement of heart rate is used by medical professionals to assist in the diagnosis and tracking of medical conditions. Heart rate measurement is one of the very important parameters of the human cardiovascular system. Electro-cardiogram (ECG) is one of frequently used and accurate methods for measuring the heart rate. ECG is an expensive device and its use for the measurement of the heart rate only is not economical [2-3]. Low-cost devices in the form of wrist watches are also available for the instantaneous measurement of the heart rate. Such devices can give accurate measurements but their cost is usually in excess of several hundred dollars, making them uneconomical. Most hospitals and clinics in the western countries use integrated devices designed to measure the heart rate, blood pressure, and temperature of the subject. Although such devices are useful, their cost is usually high and beyond the reach of individuals.

This paper describes the design of a very low-cost device which measures the heart rate of the subject by clipping sensors on one of the fingers and then displaying the result on a text based LCD. The device has the advantage that it is microcontroller based and thus can be programmed to display various quantities, such as the average, maximum and minimum rates over a period of time and so on. Another advantage of such a design is that it can be expanded and can easily be connected to a recording device or a PC to collect

and analyses the data for over a period of time. The building cost of the proposed device is around $20 [4].

II. PROPOSED BLOCK DIAGRAM A fingertip sensor, which contains an IR light emitting

diode and IR photo detector receiver. Using this device the heart rate signal can found. After getting the signal, it must be amplified, because the signal amplitude is very low. This is done using amplifier circuit. Then the amplified signal is counted by the counter using microcontroller. Finally, the signal is transmitted by the RF transmitter. Figure 1 shows the block diagram of the proposed design.

Figure 1. Block diagram of Heart rate measurement system

After transmitting the heart beat signal, it is received by the RF receiver. Then signal will be shown on the 16*2 LCD display through another amplifier.

III. PROPOSED CIRCUIT DESIGN The heart rate measurement circuit consists of two parts. One is transmitting circuit and another one is receiving circuit.

A. Transmitting Part The transmitter circuit consists of IR LED, photo diode,

MCP604, ATMEGA8, RF transmitter.

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Figure 2. Schematic of heart rate measurement and transmitting circuit

Figure 3. PCB layout (Transmitting Circuit)

Consider the figure 2, the sensor unit consists of an infrared light-emitting-diode (IR LED) and a photo diode, placed side by side, and the fingertip is placed over the sensor assembly, as shown below. The IR LED transmits an infrared light into the fingertip, a part of which is reflected back from the blood inside the finger arteries. The photo diode senses the portion of the light that is reflected back. The intensity of reflected light depends upon the blood volume inside the fingertip. So, every time the heart beats the amount of reflected infrared light changes, which can be detected by the photo diode. With a high gain amplifier, this little alteration in the amplitude of the reflected light can be converted into a pulse. The reflected IR signal detected by the photo diode is fed to a signal conditioning circuit that filters the unwanted signals and boost the desired pulse signal. The circuit diagrams above shows the IR LED (D1) and the photo diode (D2) along with the signal conditioning circuit made of two stage operational amplifiers configured as active low pass filters. The cut-off frequencies from both the filters are set to about 2.5 Hz, and so it can measure the pulse rate up to 2.5*60 = 150 bpm [4]. The gain of each filter is about 101, which gives the total 2-stage amplification of about 10000 [4]. This

is good enough to convert the weak pulsating signal into a TTL pulse. At the output is connected a LED that will blink with heart beat.

B. Receiving Part The receiving circuit consists of RF receiver, ATMEGA8

and a monitor. Figure 4 shows the receiving circuit. The ATMEGA8 runs at 8.0 MHz using internal oscillator. The two tact switches are used for Start and Clear functions. One rests his fingertip on the sensor assembly before pressing the Start button. One uses for finger or middle finger for this. Once the Start button is pressed, the microcontroller turns on the BC547 transistor (in the signal conditioning circuit). This turns the IR LED on, and the LED starts blinking with the fluctuation in the blood volume inside finger arteries. After 15 seconds, the measurement is completed and the result is transmitted to receiver circuit and it is displayed in 16*2 LCD Display.

Figure 4. Schematic of the signal receiving circuit with monitor

Figure 5. PCB layout (Receiving Circuit)

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IV. HARDWARE IMPLEMENTATION OF HEART RATE MEASUREMENT SYSTEM

This microcontroller based wireless heart bit rate measurement device has been fabricated in Printed Circuit Board (PCB).

A. Hardware design of the transmitting part Consider the figure 6; the finger will be put on the infrared

transmitter and receiver. Below the infrared transmitter there is a green LED. In the middle of the PCB there 2 buttons called start and clear. START button switches on the device whereas the CLEAR button resets all the value. On the right of the PCB there is a black chip which is the microcontroller we are using. In this PCB it is ATMEGA8. Just below the RF transmitter is placed. Below the transmitter we have the antenna. There are also 1 green and 1 red LED on both sides of the RF transmitter.

Figure 6. Hardware implementation of the heart rate measurement device (Transmitting part)

B. Hardware design of the receiving part The spiral red wire is the antenna. Beside the antenna we have our RF receiver. Below the receiver there is a green LED. Below the LED another ATMEGA8 microcontroller is used. In the below of the figure there is monitor where the output result will be shown. There’s also a reset button and by pressing it anyone can reset the value that is showing on the monitor. The receiver is shown on figure 5.

Figure 7. Hardware implementation of the heart rate measurement device

(Receiving part)

Consider the figure 5; initially the start button is pressed to switch on the device. If the device is switched on the left most green LED will be on. Then the index finger has to be put in between the infrared transmitter and receiver for 15 seconds. If the IR transmitter and receiver actually get the required amount of signal the green LED below that will flicker. As the signal acquired from the finger is very small, the signal will be amplified by MCP604. Then the amplified signal is processed by the ATMEGA8 microcontroller to produce an electrical signal related with actual measured value. Then the RF transmitter transmits the signal through the antenna. While transmitting the signal the red LED will flicker once.

V. DESIGN ALGORITHM

Figure 8. Flow chart of heart rate measurement circuit (Transmitting part)

The steps taken for measuring the heart beat and transmitting the data using the RF transmitter:

Device powered up and waited for 3 seconds so that in the meantime Display unit also turned on and showed blinking message in LCD display “Heart Beat Measurement System”.

Microcontroller will always check Start/Data Clear button is pressed or not. If nothing is pressed, the MCU will stay idle.

If Start button is pressed then a high signal is passed to turn on the BJT BC547 to start the Sensor circuit and the counting of heart beats will be started in transmitter circuit. Also ‘-‘ sign will be transmitted through RF transmitter module to inform the display unit that counting is already started to let

Start

Wait 3sec for Receiver part to Print & Blink

“Heart Beat Measurement System”

Start/Data Clear Button Pressed

Clear Previous Data& Send ‘#’

Do Nothing Start Counting (For 15sec.) &Send Start Msg. ‘-‘ Through RF Transmitter

Stop Counting &Send Stop Msg. ‘.‘ Through RF Transmitter

Count=(Heart Beat * 4)

Count<=999

Process Count Value and Send It as a string Through RF Transmitter

Send Error Msg. ‘*’

True

False

Start

Nothing Pressed

Data Clear

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know the Heart Beat Monitoring person that measurement started via LCD display unit.

After 15 seconds counting& sensor circuit will be stopped. And ‘.’ Sign will be transmitted through RF transmitter module to inform the display unit that counting is already stopped to let know the Heart Beat Monitoring person that measurement stopped via LCD display unit.

Counted value will be multiplied by 4 to get the average heart beats in a minute (BPM). And this counted value will be processed so that it can be transmitted through RF transmitter.

If counted value is greater than 999then only ‘*’ sign will be sent so that display will show that counted value is not correct. If counted value is less than 999 then the value will be passed through RF transmitted module and Transmitter circuit will be ready for next measurement.

If Data is Clear pressed any time rather than the Microcontroller is in counting loop, the transmitter clear the data that stored and will pass ‘#’ to let know the Display unit that “Data Clear” facility has been requested. The algorithm of the transmitter circuit is shown on figure 8.

Print “Error Data”

Figure 9. Flow chart of heart rate measurement circuit (Receiving part)

The steps that are taken to display measured value of heart beat and receiving the data using the Display unit are:

Device powered up and blinking message in LCD display “Heart Beat Measurement System” will be showed.

Microcontroller will always check for signals coming to RF receiver or not. Otherwise it will stay idle.

If ‘-‘sign received through RF receiver module the display unit will print “Counting started!!”via LCD display unit to let know the Heart Beat Monitoring person that measurement started.

Again Device will check for incoming signals to RF receiver.

If ‘.’ Sign is received through RF receiver module the display unit will print “Counting Stopped” via LCD display unit to let know the Heart Beat Monitoring person that measurement started.

Again Device will check for incoming signals to RF receiver. .

If ‘*’ sign is received through RF receiver module the display unit will print “Error data! ! !” If RF receiver module received a string it will process the string to get the actual counted value of Heart Beat and the display unit will print “BPM=xxx ”(xxx will be replaced with processed string value). Then it will again check for incoming signals to RF receiver.

If ‘#’ sign received through RF receiver module at any time while the Microcontroller will check for the incoming signals the display unit will print “Data Cleared!!”Via LCD display unit to let know the Heart Beat Monitoring person that “Data Clear” facility has been requested. The algorithm of the receiving circuit is shown on figure 9.

VI. PRACTICAL DEMONSTATION OF PROPOSED HEART RATE MEASUREMENT DEVICE

Figure 10 shows, when the heart beat is start to counting

Figure 10. Complete Hardware implementation (initially)

Start

Print & Blink “Heart Beat Measurement System”

Incoming Data -/#/*

Print “Data Clear”

Print “Error Data” Print

“Counting Start!!”

Print “Counting stopped”

Incoming Data String/*/#

Process String and Print “BPM= XXX(processed string

Incoming Data ./#/*

Nothing Received

# Received

# Received

# Received

# Received

# Received

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Figure 11 shows, when the heart rate measurement is finished.

Figure 11. Complete Hardware implementation (measurement finished)

Figure 12 shows, after pressing of reset button, it will clear the previous data.

Figure 12. Complete Hardware implementation (reset)

From figure 12; after transmitting the signal it is received by the receiver circuit with the help of receiving antenna. The microcontroller ATmega8 processes the signal and the output is shown in the monitor. When the receiver receives the signal, the red LED flickers once. Here the monitor is showing that

person who put his finger on the IR transmitter receiver has BPM of 64.

Figure 13. Complete Hardware implementation (Showing heart rate)

VII. CONCLUSION The microcontroller based heart beat monitoring system

using fingertip was developed to make the portable device and cheaper. A doctor can use this technology from any remote place like villages. Any non professional educated person can also operate that device. So the designed heart rate device is cheap in terms of cost also easier to understand.

REFERENCES [1] How the Heart Works, December 26, 2011. Available:http://www.webmd.com/heart-disease/guide/how-heartworks [2] John R. Hampton, “The ECG in Parctice” [3] M. Malik and A. J. Camm., “Heart Rate Variability”.Futura Publishing

Co. Inc., sept. 1995. [4] Heart rate measurement from finger trip.

Available: http://embedded-lab.com/blog/?p=1671 [5] K.Ramesh, S.V.Aswin Kumer, “ Efficient health monitoring system

using sensor networks”, International Journal of Scientific & Engineering Research Volume 3, Issue 6, June-2012.

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