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MYU Tokyo
S & M 2747

Portable Pulse Meter with Simple Design
Tian-Syung Lan,1,2* Yan Jiao,1 Xuan-Jun Dai,1**Ho-Sheng Chen,3 and Zhingqing Yang4
1College of Mechanical and Control Engineering, Guilin University of Technology, Guangxi 541004, China
2Department of Information Management, Yu Da University of Science and Technology,Miaoli County 36143, Taiwan

3College of Mechanical and Electrical Engineering, Guangdong University of Petrochemical Technology,Maoming Guangdong 525000, China

4Nanning College of Technology, Guangxi 541006, China(Received July 6, 2021; accepted October 19, 2021)

Keywords: MCU, LCD, infrared sensor, pulse signal

We aim to propose a simple design of a pulse meter. Pulse measurement is primarily based ona single-chip microcontroller unit (MCU) that receives the signal of a fingertip pulse andconverts it into electrical signals using an infrared sensor. The signals are amplified and filteredby the proposed circuit and software. The pulse meter displays the measured value on a liquid
crystal display (LCD) 1602 screen. The result with the prototype pulse meter with the proposed
circuit design and software shows an accuracy of 98.9−102.5% and a relative standard deviationof 0.82−0.90%. The proposed design provides the basis for developing further improved pulse
meters that are appropriate for mobile devices.

1.

Introduction

Pulse diagnosis is used in traditional Chinese medicine to diagnose patients’ conditions byusing three fingers (index, middle, and ring fingers) to detect the pulse on their wrist. It is known
that pathological analysis is possible with pulse diagnosis. However, doctors may have different
capabilities of diagnosing a patient’s condition by feeling the pulse with their fingers dependingon their experience and knowledge. Therefore, there are subjective factors that affect theaccuracy of diagnosis. Thus, accurate pulse diagnosis requires modern technology to develop a
more scientific and objective methodology than before. In modern medicine, heart rate and its
variability are analogous to pulse diagnosis in traditional Chinese medicine. Heart ratevariability (HRV) is an important physiological parameter for the clinical diagnosis ofcardiovascular diseases, and research on HRV has been carried out in terms of medical,electronic, and engineering technology.
With the rapid improvement of the quality of life, people pay more attention to health thanever before, which leads to the development of cost-effective medical instruments for monitoring
blood pressure, blood glucose, and so forth. They are appropriate for self-examination and selfrecording. There have been many research works on such medical instruments. Yang et al.(1)*Corresponding author: e-mail: tslan888@yahoo.com.tw**Corresponding author: e-mail: daixuanjun@163.com

https://doi.org/10.18494/SAM.2021.3537

ISSN 0914-4935 © MYU K.K.
https://myukk.org/

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used a single-chip microcomputer with Arduino to measure and record an electrocardiogram(ECG), and sent the data to a LabVIEW master computer via a wireless network for calculationand display. This instrument uses ECG patches and piezoelectric pulse wave sensors instead of
traditional inflatable cuffs, which measure blood pressure noninvasively. Peng et al.(2) designed asystem of detecting pulse rate variability on the wrist, which could be used for daily monitoring.
Chen et al.(3) designed and implemented a health detection system based on an Android
tablet，which can perform arrhythmia classification and heart rate variability analysis in realtime. A portable oximeter system based on the MSP430 microcontroller was developed by He etal.(4). This system was characterized as low cost, small size, and easy to carry. Dabbakuti(5)designed a low-power heart rate detection device based on a single programmable system onchip. Its algorithm allowed a detection rate of 1.59%, and its average power consumption was
only about 40.6 W. These research works are for exploring and developing systems withportability, low energy consumption, high detection accuracy, and low cost.
However, to the best of our knowledge, there is no research on devices or systems thatmeasure the pulse rate and blood pressure for diagnosis, because the development of thesesystems requires collecting physiological pulse signals and converting them into electricalsignals. These are then calculated using an algorithm to determine whether the heart rate isnormal. In this study, the system requires the use of infrared to measure the pulse of the humanbody. According to the difference in pulse during the relaxation and contraction of the heart, theintensity of the pulse is sensed as infrared signals by an infrared sensor. On the basis of thisprinciple, we propose a new design of a pulse meter that requires measuring, counting, anddisplaying data, and other functions indicated in Fig. 1. The new design provides a pulse meterwith the characteristics of stability and high precision as well as small size, easy to carry,compatibility with home equipment, and easy maintenance.

2.

Methods

2.1

Hardware structure

The pulse meter includes an infrared sensor that converts the measured pulse signals into
electrical ones and a single-chip control system for measurement and display. The meter includes
a signal acquisition circuit, a signal processing circuit, buttons for selection, and a liquid crystal
display (LCD) screen. The overall structure is shown in Fig. 2.

Fig. 1.

Overall structure of a pulse meter.

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Fig. 2.

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Structure diagram of pulse meter.

2.1.1 Control system
Microcontroller Unit (MCU)
The pulse meter contains a microprocessor that is controlled by a program as the chip cannot
be used alone. It relies on peripheral devices to perform properly. We selected an STC89C52
single-chip microcontroller,(6,7) which consists of a central processing unit (CPU), data memory,
program memory (ROM), a timer/counter, and I/O interfaces, as shown in Fig. 3.
Circuit Design
The control system of the pulse meter comprises a single-chip microcomputer, a crystal
oscillator circuit, and a reset circuit, which function for inputs and outputs (display). The MCU
in the pulse meter has low power consumption, small size, and easy adjustment. Figure 4 shows
the circuit design of the MCU. The system’s clock adopts the oscillating circuit with an external
crystal of 12 MHz. A 10 K resistor is used as the pull-up resistor of port P0 with an open-drain
structure. The MCU measures the pulse signal for 1 min, processes it, and transmits the result tothe display module.
Sensor
The pulse meter adopts an ST 188 sensor, the structure of which is shown in Fig. 5(a). The
ST188 sensor consists of an infrared photodiode and a highly sensitive phototransistor. A and K
are connected to an LED lamp, whereas E and C are connected to the emitter. According to theprinciple and internal structure of the reflective infrared photoelectric sensor, the circuit of thesensor is designed as shown in Fig. 5(b). With a peripheral circuit added to the sensor, theresistance is set as R1 = 330 Ω and R2 = 20 kΩ. When A outputs ‘1’ for a high-level voltage and K
outputs ‘0’ for a low-level voltage, the infrared emission tube emits infrared rays. If the receiving
tube receives the reflected infrared rays, the receiving head turns on, and E outputs a high-level
voltage, which is connected to Vcc. If the reflected infrared rays are not received, the infrared
receiver does not turn on and E outputs a low-level voltage and connects to the ground. The
characteristics of the sensor are similar to those of a photoresistor. Depending on the intensity of
the received infrared light, different voltages are generated by the sensor. When the voltage

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Fig. 3.

Structure of MCU of pulse meter.

(a)Fig. 5.

Fig. 4.

(Color online) Circuit design of MCU.

(b)(Color online) (a) Structure and (b) schematic diagram of ST188 sensor.

reaches a certain value, the triode will be in an amplified state, thereby generating differentvoltages.
Signal Acquisition Circuit
According to the working principle,(8) the pulse is measured by the sensor. When the infrared
ray passes through red blood cells, there is no reflection signal under non-hyperemia conditions.
In this case, the signal-receiving head of the sensor does not turn on and then the voltage of E is
0. Under hyperemia conditions, the penetration ability of the infrared ray becomes weak, whichenables E to turn on to transmit a high output current. In this case, the electrical signal isgenerated in the circuit and transmitted to the next module. The circuit of the signal acquisitionis shown in Fig. 6.
2.1.2 Signal processing circuit
LM385 Amplifier
The LM358 amplifier is a dual operational amplifier. It is composed of two independent highgain amplifiers that work under either a single or dual power supply. The LM358 amplifier canbe used for all conventional operational amplifiers such as variable frequency amplifiers and DC

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Fig. 6. (Color online) Signal acquisition circuit ofpulse meter.

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Fig. 7.

Structure of LM358 amplifier.

gain components. It adopts the DIP8 or SOP8 package form. The pin diagram of the LM358
amplifier is shown in Fig. 7. Pin 8 is for the main power supply input, the voltages of pins 2 and3 are compared and then output from pin 1 as OUT1. The voltages of pins 5 and 6 are comparedand then output from pin 7 as OUT2. When IN1 (+) > IN1 (−) and IN2 (+) > IN2 (−), OUT1 andOUT2 output high-level voltages. If this condition is not met, a low-level voltage is output. TheLM358 amplifier does not require a pull-up resistor, and the output voltage range is −1.5–0 V.
Signal Processing Circuit
Because the pulse signal is weak at the µV level and is usually accompanied by noiseinterference, it should be de-noised to make the signal clear. Even when the pulse signal isamplified and filtered, it still is irregular with low-frequency interference. As the irregularity
does not meet the requirement for counting by the counter, a shaping circuit should be used toremove the irregularity. We adopt a hysteresis setting for a comparator (Fig. 8) to improve theanti-interference ability. With the LM358 amplifier, an LED light indicates the status of pulse
beating.
2.1.3 Display Circuit
An LCD is used for thin and light displays owing to its physical, chemical, and opticalproperties. The main principle of the LCD is to stimulate the liquid crystal molecules with anelectric current to generate dots, lines, and planes with a backlight. The LCD enables us toobtain high-quality images and small displays. We use the LCD(9) with the circuit shown in Fig.
9. In the circuit, pins 7–14 are connected to the P0 port of the MCU for controlling the datadisplay. Ports P1.2, P1.1, and P1.0 are used for enable (EN), read and write (R/W), and register
selection (RS) of the LCD, respectively. The pulse signal is calculated by the MCU, and theresult is transmitted to the display screen.

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Fig. 8.

Fig. 9.

(Color online) Circuit for signal processing.

(Color online) Data display circuit of pulse meter.

3.

Programming

3.1

Design of main program

We use the Keil UV4 as a program compilation tool.(7,10) Because the C language is morereadable and convenient for expansion and transplantation than the assembler language, theprogram for the pulse meter is written in the C language. The program is initialized to realize thesetting of special registers, timing interrupts, and various ports. The flow chart of the system
software is shown in Fig. 10.
3.2

Design of subroutine flow

After the MCU is powered on, it initializes and clears the initial values of the previous
parameters. Then, it waits for the user to press the corresponding button and enter thecorresponding function. When the user presses the measurement button, the MCU measures thepulse rate for 15 s, calculates the corresponding pulse rate, and then displays it on the LCD
screen. When the user presses the pulse range setting button, the MCU increases or decreases
the range depending on the user’s requirements.

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Fig. 10. Flow chart of software for pulse meter.

4.

Results and Discussion

4.1

Collection of pulse signals

The human pulse is a weak low-frequency signal, so it should be amplified multiple times for
the MCU to process the signal. The pulse of the human body is in the range of 50 to 200 beats
per min with the frequency ranging from 0.83 to 3.33 Hz. Therefore, the electrical signal
measured by the infrared sensor is low. To minimize the error in detecting signals due toexternal high-frequency interference, the pulse signal must be low-pass-filtered to remove thehigh-frequency interference.
Then, for the stable operation of the pulse meter, the debugging of hardware and software isneeded depending on the system design. Hardware debugging is mainly carried out to detect
whether the short and open circuits have problems and to check the normal operation. Software
debugging is mainly carried out to detect any signal input with timing interrupt. If there is nosignal input, the software returns to the previous step where the interrupt is generated and thesoftware is rechecked for debugging. After inspection and modification, the pulse meter
becomes ready to operate normally. The prototype pulse meter manufactured in this study isshown in Fig. 12.

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Fig. 11. Flow chart of subroutine of pulse meter.

Fig. 12. (Color online) Image of prototype pulse meter.
Table 1
Measurement results.
User1
2
3

Pulse on the wrist(beats per minute)
65
72
68

164
70
69

Pulse of the finger (beats per minute)
23Average (± SD*)
6465
64.3 ± 0.577
7171
70.7 ± 0.577
7070
69.7 ± 0.577(*: Standard deviation)

The user should gently place a finger on the sensor to measure the pulse. As the pulse meterin this study has a highly sensitive sensor, the pulse of the finger can be detected. We measured
the pulses on the wrists of three different users as reference values and used a pulse meter tomeasure the pulses of the fingers. The test results are shown in Table 1. These results show thatthe accuracy of the measurement compared with the pulse on the wrist ranges from 98.9 to102.5%, and the relative standard deviation (RSD) is 0.82–0.90%. Thus, the pulse meter thatmeasures the pulse of a finger had very accurate results when used to measure the pulse of thehuman body.

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5.

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Conclusions

In this study, we propose a new design of a pulse meter by using an STC89C52
microcontroller. The design is proposed for the effective amplification, filtering, and reshapingof the pulse signal and its effective processing by the MCU. The pulse signal is measured by aninfrared sensor. The experiment result with the prototype pulse meter shows an accuracy of98.9–102.5% and an RSD of 0.82–0.90%. The proposed design and measurement result with thepulse meter provide a foundation for developing a pulse meter for accurate pulse diagnosis in
traditional Chinese medicine. The MCU proposed in this study is expected to be a basic one forfurther development of a similar pulse meter. The simple, efficient, accurate, and low-cost pulse
meter is realized for accurate pulse measurement using the design proposed in this study.

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