heartrate measurement through fingertip

Amal Jyothi College of Engineering Heart Rate Measurement

Department of Electronics and Communication Page 1

CHAPTER 1

INTRODUCTION

A heart rate monitor is a simple device that makes a sample of the heartbeat signal and computes

the bpm so that the information can easily be used to track heart conditions.

Heart rate measurement indicates the soundness of the human cardiovascular system. This project

demonstrates a technique to measure the heart rate by sensing the change in blood volume in a

finger artery while the heart is pumping the blood. It consists of an infrared LED that transmits an

IR signal through the finer tip of the subject, a part of which is reflected by the blood cells. The

reflected signal is detected by a photo transistor. The changing blood volume with heartbeat

results in a train of pulses at the output of the photo transistor, the magnitude of which is too

small to be detected directly by a microcontroller. Therefore, a two stage high gain, active low

pass filter is designed using two operational amplifiers to filter and amplify the signal to

appropriate voltage level so that the pulses can be counted by a microcontroller.



CHAPTER 2

BLOCK DIAGRAM AND EXPLANATION

2.1 BLOCK DIAGRAM

Fig: 2.1 Block Diagram of Heart Rate Measurement Circuit

2.2 MATERIALIZATION OF BLOCK DIAGRAM

2.2.1 SENSING UNIT

An optical sensor is a device that converts light rays into electronic signals. Similar to a photo

resistor, it measures the physical quantity of light and translates it into a form read by the

instrument. Usually, the optical sensor is part of a larger system integrating a measuring device, a

source of light and the sensor itself. This is generally connected to an electrical trigger, which

reacts to a change in the signal within the light sensor.

One of the features of an optical sensor is its ability to measure the changes from one or more

light beams. This change is most often based around alterations to the intensity of the light.

SENSING

UNIT AMPLIFIER

AND FILTER

MICRO

CONTROLLER DISPLAY



When a phase change occurs, the light sensor acts as a photoelectric trigger, either increasing or

decreasing the electrical output, depending on the type of sensor.

The CNY70 is a reflective sensor used in this project that includes an infrared emitter and

phototransistor in a leaded package which blocks visible light.

Fig: 2.2 Optical Reflective Sensor CNY 70

Fig: 2.3 Internal Diagram of CNY70

The CNY70 has a compact construction where the emitting light source and the detector are

arranged in the same direction to sense the presence of an object by using the reflective IR beam

from the object. 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 transistor.

2.2.2 MICROCONTROLLER

The Atmel AT89 series is an Intel 8051-compatible family of 8 bit microcontrollers (Cs)

manufactured by the Atmel Corporation.

Based on the Intel 8051 core, the AT89 series remains very popular as general purpose

microcontrollers, due to their industry standard instruction set, and low unit cost. This allows a

great amount of legacy code to be reused without modification in new applications. While

considerably less powerful than the newer AT90 series of AVR RISC microcontrollers, new

product development has continued with the AT89 series for the aforementioned advantages.

All four ports in the AT89C51 and AT89C52 are bidirectional. Each consists of a latch (Special

Function Registers P0 through P3), an output driver, and an input buffer. The output drivers of

Ports 0 and 2, and the input buffers of Port 0, are used in access to external memory. In this

application, Port 0 outputs the low byte of the external memory address, time-multiplexed with

the byte being written or read. Port 2 outputs the high byte of the external memory address when

the address is 16 bits wide. Otherwise the Port 2 pins continue to emit the P2 SFR content. All

the Port 3 pins, and two Port 1 pins (in the AT89C52) are multifunctional. The alternate

functions can only be activated if the corresponding bit latch in the port SFR contains a 1.

Otherwise the port pin is stuck at 0. It has less complex feature than other microprocessor.

In this project, it is used to count the pulses reached at its input port. The output of the sensing

unit which consists of the sensor, amplifier, filter and comparator is given to the input of the

microcontroller. A seven segment display is connected at its port 2 in which the final output

count of the pulses are shown.

2.2.3 SEVEN SEGMENT DISPLAY

The seven elements of the display can be lit in different combinations to represent the Arabic

numerals. Often the seven segments are arranged in an oblique (slanted) arrangement, which aids



readability. The numerals 6, 7 and 9 may be represented by two or more different glyphs on

seven-segment displays, with or without a 'tail'.

The seven segments are arranged as a rectangle of two vertical segments on each side with one

horizontal segment on the top, middle, and bottom. Additionally, the seventh segment bisects the

rectangle horizontally. There are also fourteen-segment displays and sixteen-segment displays

(for full alphanumeric); however, these have mostly been replaced by dot matrix displays.

The segments of a 7-segment display are referred to by the letters A to G, where the optional

DP decimal point (an "eighth segment") is used for the display of non-integer numbers.

Seven-segment displays may use a liquid crystal display (LCD), a light-emitting diode (LED) for

each segment, or other light-generating or controlling techniques such as cold cathode gas

discharge, vacuum fluorescent, incandescent filaments, and others. For gasoline price totems and

other large signs, vane displays made up of electromagnetically flipped light-reflecting segments

(or "vanes") are still commonly used.

In a simple LED package, typically all of the cathodes (negative terminals) or all of

the anodes (positive terminals) of the segment LEDs are connected and brought out to a

common pin; this is referred to as a "common cathode" or "common anode" device. Hence a 7

segment plus decimal point package will only require nine pins (though commercial products

typically contain more pins, and/or spaces where pins would go) in order to match

standard IC sockets. Integrated displays also exist, with single or multiple digits. Some of these

integrated displays incorporate their own internal decoder, though most do not: each individual

LED is brought out to a connecting pin as described.

Fig:2.4 Individual Segment of a Seven Segment Display



All the anodes of the A segments of each digit position would be connected together and to

a driver circuit pin, while the cathodes of all segments for each digit would be connected. To

operate any particular segment of any digit, the controlling integrated circuit would turn on the

cathode driver for the selected digit, and the anode drivers for the desired segments; then after a

short blanking interval the next digit would be selected and new segments lit, in a sequential

fashion. In this manner an eight digit display with seven segments and a decimal point would

require only 8 cathode drivers and 8 anode drivers, instead of sixty-four drivers and IC pins.

A single byte can encode the full state of a 7-segment-display. The most popular bit encodings

are GFEDCBA and ABCDEFG, where each letter represents a particular segment in the

display. In the GFEDCBA representation, a byte value of 0x06 would (in a common-anode

circuit) turn on segments 'C' and 'B', which would display a '1'.



CHAPTER 3

CIRCUITRY

3.1 CIRCUIT DIAGRAM 1: SENSING UNIT

Fig:3.1 Sensing Unit



3.2 CIRCUIT DIAGRAM 2: COUNTING UNIT

Fig:3.2 Counting Unit



3.4 COMPONENTS LIST

Table:3.1 Resistors

Specification Quantity

1M 1

1K 1

68K 2

18K 3

6.8K 1

470 3

100 2

Table:3.2 Capacitors

Specification Quantity

0.47F 2

0.1F 1



Table:3.3 Miscellaneous

Miscellaneous Specification Quantity

Optical sensor CNY70 1

Op-Amp LM358 2

LED 1

Micro controller AT89C51 1

Transistors 2N2222 2



CHAPTER 4

PIN DIAGRAMS

4.1 AT89C51

Fig: 4.1 Pin Diagram of AT89C51

DESCRIPTION

AT89C51 is an 8-bit microcontroller and belongs to Atmel's 8051 family. ATMEL 89C51 has

4KB of Flash programmable and erasable read only memory (PEROM) and 128 bytes of RAM.

It can be erased and program to a maximum of 1000 times. In 40 pin AT89C51, there are four

ports designated as P1, P2, P3 and P0. All these ports are 8-bit bi-directional ports, i.e., they can be

used as both input and output ports. Except P0 which needs external pull-ups, rest of the ports

have internal pull-ups. When 1s are written to these port pins, they are pulled high by the internal



pull-ups and can be used as inputs. These ports are also bit addressable and so their bits can also

be accessed individually.

Port P0 and P2 are also used to provide low byte and high byte addresses, respectively, when

connected to an external memory. Port 3 has multiplexed pins for special functions like serial

communication, hardware interrupts, timer inputs and read/write operation from external

memory. AT89C51 has an inbuilt UART for serial communication. It can be programmed to

operate at different baud rates. Including two timers & hardware interrupts, it has a total of six

interrupts.

VCC: Positive (+ve) DC Supply voltage. Which is normally between 3V to 5V DC.

GND: 0V Ground. This pin is connected to negative (-ve) DC supply voltage.

PORTS: Ports are generally used by computers to communicate to the outside world.

Microcontrollers use port to read input from another device or to send output to another device.

AT89C51 has four ports for communication.

PORT 0, PORT 1, PORT 2, PORT 3: These ports are 8-bit bi-directional I/O ports. They can be used

for both input and output ports. As an output port, each pin can sink eight TTL inputs. Port can

be used as an input when they are made to read data from another device (which can be a

component or a sensor), or as an output when they are used to send a signal to another device.

They basically understand two logic states that is 1s and 0s.

RST: Reset input. This pin is used to reset the microcontroller. If a high remains on this pin for

two machine cycles while the oscillator is running, the microcontroller is reset.

ALE/PROG: Address Latch Enable output pulse for latching the low byte of the address during

access to external memory. This pin is also the program pulse input (PROG) during Flash

programming. This pin used to program the microcontroller. Setting the ALE-disable bit has no

effect if the microcontroller is in external execution mode.

PSEN: Program Store Enable is the read strobe to external program memory. When the AT89C51

is executing code from external program memory, PSEN is activated twice each machine cycle,

except that two PSEN activations are skipped during each access to external data memory.



EA/VPP: External Access Enable. A must be strapped to GND in order to enable the device to

fetch code from external program memory locations starting at 0000H up to FFFFH. Note,

however, that if lock bit 1 is programmed, EA will be internally latched on reset. EA should be

strapped to VCC for internal program executions. This pin also receives the 12V programming

enable voltage (VPP) during Flash programming, for parts that require 12V VPP.

XTAL1: Input to the inverting oscillator amplifier and input to the internal clock operating circuit.

This pin is connected to the external crystal oscillator together with XTAL2.

XTAL2: Output from the inverting oscillator amplifier.



ARCHITECTURE OF AT89C51

Fig: 4.2 Architecture of AT89C51



4.2 LM358

Fig: 4.3 Pin Diagram of LM358

LM358 is a dual operational amplifiers feature low power drain, a common mode input voltage

range extending to ground/VEE, and single supply or split supply operation. The LM358 series is

equivalent to one-half of an LM324.

These amplifiers have several distinct advantages over standard operational amplifier types in

single supply applications. They can operate at supply voltages as low as 3.0 V or as high as 32

V, with quiescent currents about onefifth of those associated with the MC1741 (on a per

amplifier basis). The common mode input range includes the negative supply, thereby

eliminating the necessity for external biasing components in many applications. The output

voltage range also includes the negative power supply voltage.



4.3 CNY70

Fig: 4.4 Optical Sensor CNY70

The CNY70 is a reflective sensor that includes an infrared emitter and phototransistor in a leaded

package which blocks visible light. Its dimension is described as L7 mmW7 mmH6 mm and

its peak operating distance is less than 0.5mm. Also its emitter wavelength is about 950nm.

The CNY70 has a compact construction where the emitting light source and the detector are

arranged in the same direction to sense the presence of an object by using the reflective IR beam

from the object.



CHAPTER 5

ADVANTAGES AND DISADVANTAGES

5.1 ADVANTAGES

Ergonomic.

Cost Effective.

Durable.

Portable.

Simple.

Can be used in clinical & non-clinical environments.

5.2 DISADVANTAGES

Noise may produce disturbance.

Resting heart rate is subject to high variability thus causing error.

Continuous monitoring is not possible.

5.3 PROBLEMS FACED

The major problem faced during the development of our project was the difficulty in making

up a pulse sensing circuit. The IR diode was sensing the object movement but not the

variation of blood flow. By adding a comparator unit and by proper designing of the whole

circuit leads us to overcome the same. The interference of the visible light and surrounded

noise makes the development of the sensing unit to be the greatest challenge.



CHAPTER 6

CONCLUSION

In this project, the design and development of a Heart Rate Measuring device is presented. It

measures the heart rate efficiently in a short time and with less expense without using time

consuming and expensive clinical pulse detection systems. Analog signal processing techniques

are used to keep the device simple and to efficiently suppress the disturbance in signals.

Experimental results showed that the heart rate can be filtered and digitized so that it can be

counted to calculate an accurate pulse rate. The device is able to detect, filter, digitize, and

display the heartbeat of a user ergonomically.

The device could be further developed into a continuously monitoring device that could be used

to detect the heart rate anomalies associated with certain heart conditions. The maximum and

minimum heart rates over a period of time and thus any abnormalities in the pulse rate can also

be detected.



REFERENCES

BOOKS

J.B. Gupta: Electronic circuits and devices.

Ramakanth A. Gayakward: Op-amps and linear integrated circuits.

K.R. Botkar: Integrated circuits.

Muhammad Ali Mazidi, Janice Gillispie Mazidi and Rolin D Mckinlay: The 8051 Microcontroller and Embedded Systems, Pearson Prentice Hall Publication.

Udayashankara: 8051 Microcontroller; Hardware, Software & Applications.

WEBSITES

www.electronicsforyou.com

www.electronicshub.com

www.wikipedia.com



APPENDIX

heartrate measurement through fingertip

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