APEC Youth Scientist Journal Vol. 8, No. 1, February 2016, pp. 44~47

http://www.sigs.or.kr

ISSN 2005-5625(Online)

Low-Cost Photoplethysmographic Circuit for Heart Rate

Measurement

Reisha Claffel Z. Ferraren* and Lindly Van S. Medrano

Philippine Science High School - Central Visayas Campus, Talaytay, Argao, Cebu, Philippines

(Received December 19, 2015 : Revised March 12, 2016 : Accepted March 15, 2016)

ABSTRACT: Heart rate measurement helps in assessing the condition of the cardiovascular system.

Today, there are many other methods to measure heart rates such as Phonocardiogram, ECG, blood pres-

sure wave form, and pulse meters but these methods are clinical and expensive. Because of these, a need

exists for cheap sensing devices that can measure pulse in an accurate but much easier way. In this study, a

low-cost photoplethysmographic circuit was fabricated with the use of LM358 Operational Amplifier, photo-

diode, infrared LED, resistors, and potentiometers. The heartbeats per minute of five volunteers were

recorded. Three trials were done per volunteer. Data showed that the average heartbeats per minute for the

five volunteers with standard deviations are 67.33 ± 1.53, 63.00 ± 2.00, 65.67 ± 2.52, 70.33 ± 1.53, and

65.33 ± 1.53 respectively. The fabricated circuit successfully measured the heart rates of five people. The

experiment established the potential of low-cost do-it-yourself photoplethysmographic circuits as alterna-

tives to the expensive medical heart rate devices currently being used in hospitals and clinics.

Key words: photoplethysmographic, pulse, heart, rate

INTRODUCTION

Background of the Study

Heart rate indicates the soundness of our heart and helps assessing the condition of cardiovascular

system (Landaeta et al., 2006). The recording of the pulses of blood vessels in human beings or electro-

cardiograms has been an integral part of medicine to both doctors and researchers since its inception. A

thorough understanding of the physiology and properties of blood vessels can provide a framework for

understanding the nature of pulses (http://www.aub.edu.lb/fea/ece/research/Documents/Report/fyp_0506/

6_Report.pdf).

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, ECG, blood

pressure wave form, and pulse meters but these methods are clinical and expensive (Hashem et al., n.d.).

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 (Ibrahim and Buruncuk, n.d.).

Because of the aforementioned problems, a need exists for a low-cost sensing device that can measure

pulse in an accurate but much easier way. In this study, a photoplethysmographic circuit board, which

consists of a LM358 Operational Amplifier, photodiode, infrared LED, resistors, and potentiometers, was

fabricated to measure the heart rate of a person from his or her finger.

*E-mail: reishaferraren@yahoo.com

Low-Cost Photoplethysmographic Circuit for Heart Rate Measurement 45

Objectives of the Study

This study mainly aimed to fabricate and test a low-cost photoplethysmographic circuit in measuring the

heart rate of a person from his or her finger. Specifically, it aimed to:

(1) measure the heart rate of five people or volunteers; and

(2) evaluate the efficiency of the sensor by comparing the results to the available records by Ostchega et al.

(2011).

Significance of the Study

The heart rate of a person evaluates his or her cardiovascular system. Due to this, being able to know

one’s heart rate easily and quickly has been a growing necessity for the young and the adults alike.

Nowadays, most expensive phones have been equipped with heart rate sensors, which still makes the

availability of heart rate sensors limited. This study may provide better alternatives in measuring one’s

heart rate without the high cost. The application of infrared LED and photodiodes also show potential for

their various uses in different fields.

Scope and Limitations

The materials used for the photoplethysmographic circuit were bought from Teknica Electronics, Cebu

City, Philippines. This study tested the device with only five people. Only the heartbeats per minute were

detected and recorded by the photoplethysmographic circuit.

MATERIALS AND METHODS

Construction of Photoplethysmographic Circuit

A 1.9 in. by 2.8 in. Plastic Circuit Board (PCB) was utilized for mounting the whole circuit. For the

circuit, one 100k Ohms, one 10k Ohms, one 2.4k Ohms, one 330 Ohms, one 100 Ohms, and two 10K

Ohms potentiometers are used. A 50mW at 100mA infrared LED with wavelength of 830nm and a photo-

diode with silicon pin were placed in a clip and then connected to the circuit, which is mainly composed of

an LM358 Operational Amplifier. The overall circuit is shown in Fig. 1. The physical appearance of the

fabricated circuit is shown in Fig. 2.

Testing of Fabricated Sensing Device

Five volunteers within the age bracket of 14 to 16 years old had tested the device while they were at

rest. For each person, three trials were conducted. The heart rate values per minute were recorded.

Fig. 1. The overall circuit diagram of the fabricated photoplethysmographic sensor.

46 Reisha Claffel Z. Ferraren and Lindly Van S. Medrano

RESULTS AND DISCUSSION

Operational amplifiers work by taking two different incoming signals and amplifying the difference

between it (Renevey et al., 2007). In the circuit, it is in between the 7th pin and the 6th pin. Thus, the gain

is calculated by:

(Equation 1)

Gain = 1 + 2 =3

Since fingers from different people are to be tested, the signal in the 5th pin of the LM358 Amplifier varies.

Different fingers shall give different signals. After the signal is amplified, it comes out in the 7th pin, carrying

the pulse.

Table 1 shows the recorded heartbeats per minute of each volunteer for each of the trials done together

with the average heartbeats per minute of each person with standard deviation. The obtained results were

near to the mean resting pulse rates recorded by Ostchega et al. (2011) for adolescents aged 16-19, which

are 72 beats/min for males and 79 beats/min for females.

CONCLUSION AND RECOMMENDATIONS

A low-cost photoplethysmographic circuit was successfully fabricated and tested. The gathered data

established the functionality and potential of the said circuit as a practical option in replacing expensive

medical heart rate devices.

It is recommended that other data be gathered such as the numbers that appear normally on the circuit

when there is no person being tested. It is also recommended that more volunteers be tested to accurately

evaluate the performance of the fabricated circuit.

Gain 1R4

R3

-----+=

Fig. 2. The physical appearance of the fabricated photoplethysmographic sensor.

Table 1. Heartbeats per minute of the five volunteers measured by the fabricated photoplethysmographic sensor.

VolunteerNumber

Heartbeats per minute (Trial 1)

Heartbeats per minute (Trial 2)

Heartbeats per minute (Trial 3)

Average Heartbeats per minute ± SD

1 67 69 66 67.33 ± 1.53

2 63 61 65 63.00 ± 2.00

3 66 63 68 65.67 ± 2.52

4 72 69 70 70.33 ± 1.53

5 65 64 67 65.33 ± 1.53

Low-Cost Photoplethysmographic Circuit for Heart Rate Measurement 47

ACKNOWLEDGEMENTS

The researchers would like to thank the following: Mr. Benito A. Baje, for the unforgettable AMGS journey

and for being the researchers’ official adviser; Enthusiastic Inventors and Sci-Tech Innovators (EINSTEIN)

Club of PSHS-CVisC; friends and families especially, Mrs. Reggie S. Medrano, Mrs. Catherine Z. Ferraren,

and Mr. Rogelio O. Ferraren Jr., for the help and support they have given for this study to be a successful

one; and of course, The Almighty Father, for everything.

REFERENCES

[1] Anonymous. (n.d.). Optical instrument for measuring frequency of vibration. Retrieved from http://www.aub.edu.lb/

fea/ece/research/Documents/Report/fyp_0506

[2] Hashem, M.M.A, Shams, R., Kader, M.A. and Sayed, M.A. (n.d.). Design and development of a heart rate mea-

suring device using fingertip. Retrieved from http://arxiv.org/pdf/1304.2475

[3] Ibrahim, D. and Buruncuk, K. (n.d.). Heart Rate Measurement from the Finger Using a Low-cost Microcontroller.

[4] Landaeta, R..G., Casas O., and Areny, R.P. (2006). Heart rate detection from plantar bioimpedance measurements.

28th IEEE EMBS Annual International Conference, USA, pp. 5113-5116.

[5] Ostchega, Y., Porter, K.S., Hughes, J., and Dillon, C.F. (2011). Resting pulse rate reference data for children, ado-

lescents, and adults: United States, 1999 - 2008. National Health Statistics Reports.

[6] Renevey, P., Vetter, R., Krauss, J., Celka, P., Gentsch, R., and Depeursinge, Y. (2007). Wrist-located pulse detec-

tion using IR signals, activity and nonlinear artifact cancellation. Swiss Center of Electronics and Microtechnol-

ogy, CSEM, Neuchˆatel, Switzerland.

Reisha Claffel Z.

Ferraren

Lindly Van S.

Medrano