Design of the hottest digital human heart rate det

2022-08-09
  • Detail

Design of digital human heart rate detector

introduction

although there are many instruments for detecting heart rate at present, there are few portable full digital heart rate measuring devices that can realize accurate measurement, upload data to PC and have various functions such as audible and visual alarm. The digital human heart rate detector introduced in this paper can accurately measure the number of heartbeats in the hands, wrists, arms and other parts of the human body. At the same time, it also has many functions, such as power down storage, measurement data upload to PC, audible and visual alarm and so on

1 system composition and working principle

the system composition is shown in Figure 1. When the stroke of this design is 800mm, it can count the signal affected by the friction force of the oil cylinder mainly controlled by the single chip microcomputer, supplemented by a small number of hardware circuits, to complete the functions of data processing, memory, display, communication and so on

first, set the working mode of the system through the keyboard when the system starts up, and then input the human heartbeat signal detected by the piezoelectric ceramic chip to the single chip microcomputer after being amplified, filtered and shaped at the same time. The single chip microcomputer processes the measured data and sends it to the display circuit for display. At the same time, the measured data is uploaded to the PC through the communication circuit. The memory circuit is mainly used to store the measured data and realize the function of power down storage, The audible and visual alarm circuit will alarm when the measured data exceeds the normal range (such as more than 180 times/min or less than 45 times/min) to remind doctors

2 system hardware circuit design

2.1 sensor and signal processing circuit

sensor and signal processing circuit are shown in Figure 2

the sensor for detecting the heart rate pulse signal adopts piezoelectric ceramics (a sea pad is installed on the piezoelectric ceramic sheet to transmit the pulse signal); The collected heart rate signal is amplified by a three-stage amplification circuit composed of three non gates of CD4069, and then filtered by a two-stage trapezoidal filter circuit composed of R4, R5, C5 and R7, R8, C6, so as to obtain the signal of the human heart rate range (about 0.66hz-3.33hz); After being processed by the detection circuit composed of diodes D1, D2 and R6 and the shaping circuit composed of three non gates u1f, u1d and u1e, the standard V-pulse signal required by the single chip microcomputer can be obtained

2.2 keyboard circuit

the keyboard circuit is shown in Figure 3

because the i/o is sufficient, the four keys are connected to P1.2, p1.3, P1.4 and P1.5 of the single chip microcomputer respectively, and the query method is used to work. K1, K2, K3 and K4 complete the operations of starting measurement, querying, storing measurement structure and clearing memory data respectively, and the data shows the linear improvement of waterproof performance

2.3 display circuit

the display circuit is shown in Figure 4. The dynamic display mode is adopted. The data input terminals of the two 74ls373 in the figure are connected to the P0 port of 89C51 single chip microcomputer. The single chip microcomputer provides chip selection signals to the two 74ls373 through P1.0 and p1.3, so as to realize the time-sharing selection of two 74ls373, and transmit segment code and bit code respectively. In the figure, there are 6 nixie tubes, the first 3 are used to display the serial number of the tested person, and the last 3 are used to display the heartbeat times per minute; ULN2803 is an 8-bit inverted driver, which acts as a bit enhanced driver

2.4 memory storage circuit

see Figure 5 for memory storage circuit. The memory chip adopts AT24C02. SDA is the serial data input/output pin, SCL is the serial synchronous clock input end; A0, A1 and A2 are chip selection signal input terminals, and the test pin is write protected. When grounded, it means no protection. When you want to save the heart rate data after measuring, press the storage key K3, and the single chip microcomputer will provide the appropriate clock to AT24C02 through p2.1, and then store the data in the specified address. Of course, the control word, address and data are input in three times, and AT24C02 is required to provide a response signal to the single chip microcomputer between each segment. In addition, start and stop bits should be added before and after reading and writing data

2.5 communication circuit

the function of communication circuit is to upload the heart rate data measured by single chip microcomputer to PC. This circuit uses a MAX232 chip to convert the TTL level into the level that can be recognized by PC, and then connects with PC through a standard 9-pin interface. The peripheral circuit is rich and simple, only five 0.1 μ The specific circuit of the capacitor of F is shown in Figure 6

2.6 audible and visual alarm circuit

see Figure 7 for audible and visual alarm circuit. The NAND gate 74f00 constitutes a 2-stage gated oscillator. Among them, u6a and u6b form a low-frequency oscillator with an oscillation frequency of about 1Hz. R5 is a pull-down resistor, making uc=0v under normal conditions. Only when the measured data is within the alarm range, a high-level circuit provided by P1.6 of the single chip microcomputer starts to vibrate. The high and low levels alternately output at B0 end make the LED flash through Q1. U6c and u6d form an audio oscillator with an oscillation frequency of about 1kHz. Only when b0=1, the second stage oscillator starts to vibrate, and the speaker BL is driven by Darlington tube Q2 and output transformer T to produce intermittent "tick, tick..." alarm sound

3 software design

the main program flow chart of the system is shown in Figure 8

mainly includes display driver, key handler, INT0 interrupt service program, AT24C02 driver storage program, serial port communication program, etc

4 Conclusion

through the actual design and production, and compared with the existing heart rate detector in the market, the results show that this design has the advantages of small size, light weight, low cost, convenient use, accurate measurement and so on, and has a good application prospect. (end)

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