Design of heart rate acquisition and monitoring system for smart clothing

Abstract: Combining smart clothing and wireless sensor network technology, a new type of photoelectric reflection type analog sensor is used to design a heart rate acquisition and monitoring module that can be carried around. The module can not only collect the pulse heart rate in real time, but also send the collected data to the upper computer to realize remote real-time monitoring. When the monitored value exceeds or falls below the normal threshold, an alarm signal will be sent to facilitate rescue workers in time. . This heart rate acquisition module is small, easy to carry, and embedded in the clothing design. It can also be applied to many fields such as medicine and field exploration. This design is another emerging product of the combination of clothing art and wireless electronics. Important practical significance.

0 Preface

Since 2013, smart watches, bracelets, and glasses have gradually entered the public's field of vision, becoming the target of “influx people”. This year, it was recognized by the industry as “the first year of wearable devices”. In simple terms, a wearable device is a portable device that can be worn directly on the body or integrated into the user's clothing or accessories. However, with the development of wireless sensor technology, a variety of wearable smart clothing is gradually appearing in people's lives. Smart clothing is to embed small chips, electronic components, power supplies and other equipment into the clothing, which can be realized. Specific functions to facilitate people's lives [1]. The heart rate acquisition and monitoring module designed in this paper adopts the most advanced photoelectric reflection sensor on the market. It is different from the conventional piezoelectric and film sensor and has high sensitivity. At the same time, this paper specially designed the pocket of the garment, and placed the pulse sensor to collect and monitor the pulse of the human body more conveniently.

1 photoelectric reflection sensor working principle

Pulsesensor is a photoelectric reflective analog sensor for pulse heart rate measurement. The signal is collected by the principle of the photoelectric volume method, and is worn on a finger or an earlobe, and the pulse is measured by utilizing the difference in transmittance of the human tissue when the blood vessel beats. Since the pulse is a signal that periodically changes with the heart's pulsation, the arterial volume also changes periodically, so the electrical signal change period of the photoelectric transducer is the pulse frequency [2].

1.1 System function module division

The functional modules of the overall system are divided as shown in Figure 1, including the acquisition module, micro-processing module, wireless data transceiver module, liquid crystal display module and serial communication module.

Heart rate acquisition and monitoring system design for smart clothing

1.2 Design of the shaping circuit

The shaping circuit of the system uses a four-voltage comparator LM339 and a plurality of resistors and capacitors to form a single-limit voltage comparison circuit [3]. Figure 2 shows the circuit schematic of the shaping part. Since the pulse signal is shaped into a square wave signal with an amplitude of 2~3 V, it is appropriate to set the threshold voltage to 2.5 V. The whole circuit is +5 V DC. The voltage source is powered. After experimental measurement, the optimum value of R2 is 10 kΩ. The shaping circuit can conveniently realize the statistics of the pulse number and provide conditions for the monitoring of the upper computer.

Heart rate acquisition and monitoring system design for smart clothing

2 Heart rate signal processing module design

In order to get the correct pulse rate, you can use the means of setting the interrupt to achieve the function [4]. Set I/O port P1.3 as an external interrupt port. The falling edge of the input signal can trigger an external interrupt to make the system enter the external interrupt service subroutine. Each time the service subroutine pulse counter is incremented by 1, the timer 1 timer user Custom time period. Once the timing time is reached, the value in the counter is read, and after reading, the registers are cleared for the next count. FIG. 3 is a flowchart of the coordinator of the pulse acquisition module of the system, and FIG. 4 is a flow chart of the heart rate acquisition process.

Heart rate acquisition and monitoring system design for smart clothing

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