Design of physiological intelligent monitoring and early warning system for the elderly based on SC89F5162 multi-sensor data fusion

　　At present, population aging has become a prominent social problem in today's world. The World Health Organization pointed out that among more than 190 countries and regions in the world, more than 60 have entered an aging society. The biggest threat to the health of the elderly - the death toll caused by cardiovascular disease accounts for one-third of the global death toll. Various cardiovascular diseases will have corresponding signs before the onset of the disease, and these signs can be discovered by observing the patient's physiological parameter data. Therefore, designing a medical instrument that can monitor the main physiological parameters and has an alarm function will provide a new means for preventing and treating various sudden diseases. At present, physiological parameter monitoring equipment is mostly used in hospital intensive care units, nursing homes, etc., which can monitor the important physiological parameters of patients or the elderly in real time, continuously and for a long time. Some monitoring equipment also has a certain local alarm function. However, it is slightly lacking in remote wireless alarm function and does not support mobile phone SMS alarm function. This monitoring system has both accurate monitoring function and mobile phone GPRS alarm function, which can be used in daily homes to meet the needs of the elderly for such equipment.

　　2. Project Design Principles

　　1. Principle Overview

　　The system uses external flame sensors, acceleration sensors, and heart rate sensors to obtain data such as whether there is a fire source around the elderly, whether they have fallen, whether their heart rate is normal, etc. Once the system detects an abnormality in the external sensor, it will use the external GPS and GSM/GPRS module to send the elderly's location information and heart rate data to their relatives through the GSM/GPRS module, so that children can obtain the elderly's information in time.

　　Traditional elderly care systems can only monitor the living conditions of the elderly at home and cannot obtain information when the elderly are outside. This system is integrated with a GPS module, so that once an elderly person has an accident, his or her location can be determined in time and the GSM/GPRS module can be used to send information to notify his or her family. In addition, traditional elderly care monitoring systems can only detect whether one data is normal, such as heartbeat, and cannot obtain multiple detection data. The system we designed can realize the fusion of multi-sensor networking and multi-data, that is, the data measured by the flame sensor, acceleration sensor, and heartbeat sensor can be integrated with the location information obtained by GPS and sent out together. The design is light and compact, with low production cost and complete functions, which can fully meet the wishes of those children who "want to support their parents but they are not around".

　　2. Hardware Principle Overview

　　A. Core controller: This project uses a high-speed and high-efficiency 8051-compatible microcontroller model SC89F5162 independently developed by Shenzhen Lianhua. At the same oscillation frequency, it has the characteristics of faster operation and better performance than the traditional 8051 chip. SC89F5162 retains most of the features of the standard 8051 chip, including built-in 256 bytes of RAM and 2 16-bit timers/counters, 1 UART and external interrupts INT0 and INT1. In addition, SC89F5162 also integrates an external 1024-byte RAM, which is compatible with the 16-bit timer/counter (Timer2) of the 8052 chip. The microcontroller also includes a 62K-byte Flash memory suitable for programs and data. SC89F5162 not only integrates standard communication modules such as EUART, SPI, but also integrates ADC with built-in comparison function, PWM timer and analog comparator (CMP) and other modules. In order to achieve high reliability and low power consumption, a watchdog timer, low voltage reset function, low voltage detection function and oscillator failure detection function are built in. In addition, two low power saving modes are provided.

　　B. Principle of using acceleration sensor to measure falls: Human acceleration can be regarded as a three-dimensional vector, represented by the three axes of a rectangular coordinate system, where the X axis represents the front-to-back direction, the Y axis represents the left-to-right direction, and the Z axis represents the vertical direction. Here, we first introduce the concept of the signal vector modulus (SVM) of acceleration, formula (1):

　                                                   　(1)

　　When a fall occurs, before touching the ground, due to the weightlessness of the body, its SVM appears as a valley in the time domain; during the entire process of touching the ground, due to the impact of the ground, the acceleration of the human body will inevitably undergo a more drastic mutation, and its SVM appears as a peak in the time domain. The fall signal has an obvious SVM in the time domain, and there is an obvious impact at the fall, as shown in the figure below. In this case, the threshold judgment in the time domain can well detect the occurrence of the fall.

　　C. Principle of flame sensor: It is composed of high-temperature solid particles mainly composed of various combustion products, intermediates, high-temperature gases, hydrocarbons and inorganic substances. The thermal radiation of flame has discrete spectrum of gas radiation and continuous spectrum of solid radiation. The flame radiation intensity and wavelength distribution of different combustion materials are different, but in general, the near-infrared wavelength domain and ultraviolet domain corresponding to the flame temperature have great radiation intensity. According to this characteristic, a flame sensor can be made.

　　This project uses a flame sensor module, which has an embedded LM393 comparator. The module can directly output a level signal (5V or 0V), making it convenient to connect the module directly to the IO port of the microcontroller. The figure below shows the output waveform displayed by an oscilloscope.

　　D. GPS module: The Global Positioning System (GPS) is a new generation of satellite navigation system in the United States. It can provide users with a global, all-weather, continuous satellite radio navigation system that can provide real-time three-dimensional position, three-dimensional speed and high-precision time information. The GPS receiver receives navigation information broadcast by any number of satellites within its line of sight and converts its own position and time information.

　　This project uses a high-performance GPS positioning module model ATK-NEO-6M-V12. The module uses the U-BLOX NEO-6M module, which comes with a high-performance passive ceramic antenna and a rechargeable backup battery (to support warm start or hot start. The backup battery can maintain GPS reception data storage for about half an hour after the main power is cut off). The following figure shows the communication between this module and the U-center software to obtain positioning information.

　　E. Pulse sensor: The external pulse sensor uses the sensitive characteristics of infrared rays of a specific wavelength to the changes in blood volume caused by the microcirculation of blood at the end of blood vessels to detect the corresponding changes in blood volume at the fingertips caused by the beating of the heart. After signal amplification, conditioning and other circuit processing, it outputs a complete pulse wave voltage signal that reflects the changes in blood volume at the fingertips. This infrared pulse sensor is mainly used for the measurement and monitoring of pulse rate and pathological analysis of pulse waves in clinical practice.

　　F. GSM/GPRS communication module: This project uses the new compact product SIM900A launched by SIMCom. It is a dual-band GSM/GPRS module that is completely packaged in SMT. SIM900A is only suitable for the Chinese market. It has stable performance, exquisite appearance, high cost performance, and can meet a variety of design requirements. SIM900A uses an industrial standard interface and an operating frequency of GSM/GPRS 850/900/1800/1900MHz. It can realize the transmission of voice, SMS, data and fax information with low power consumption. In addition, the size of SIM900A is 24x24x3mm, which is particularly suitable for compact product design.

　　3. Software design principles

　　The software design of this topic is divided into two parts: 1. MCU program design: The development environment of the MCU driver designed based on the subsystem function is Keil4, and the development language is C. The MCU driver uses the SC89F5162's S input/output (I/O) quasi-bidirectional mode, enhanced universal asynchronous receiver/transmitter (EUART) and analog/digital converter (ADC) and other special features.

　　Enhanced Universal Asynchronous Receiver Transmitter (EUART) design principle: EUART first converts the received parallel data into serial data for transmission. The message frame starts with a low start bit, followed by 5 to 8 data bits, an available parity bit and one or more high stop bits. When the receiver finds the start bit, it knows that the data is ready to be sent and tries to synchronize with the transmitter clock frequency. If parity is selected, UART adds the parity bit after the data bit. The parity bit can be used to help error checking. During the reception process, UART removes the start and end bits from the message frame, performs parity check on the incoming bytes, and converts the data bytes from serial to parallel. UART also generates additional signals to indicate the status of sending and receiving. For example, if a parity error occurs, UART sets the parity flag. Based on this principle, the relevant registers and setting parameters of EUART are reasonably configured.

　　Analog/digital converter (ADC) software design principle: SC89F5162 contains a single-ended, 10-bit successive approximation analog-to-digital converter (ADC). The built-in reference voltage VREF of the ADC is directly connected to VDD, and the user can also select the VREF port to input the reference voltage. The 8 ADC channels can input analog signals independently, but only one channel can be used for each conversion. The GO/DONE signal controls the start of conversion and prompts the end of conversion. When the conversion is completed, the ADC data register is updated. At the same time, the ADCIF bit in the ADCON register is set, and an interrupt is generated (if the ADC interrupt is allowed). The ADC module integrates a digital comparison function to compare the analog input value in the ADC with the digital value. If the digital comparison function is allowed (the EC position in the ADCON register is set to 1) and the ADC module is enabled (the ADON position in the ADCON register is set to 1), the ADC interrupt will only be generated when the digital value of the corresponding analog input is greater than or equal to the comparison value (ADDH/L) in the register. When GO/DONE is set to 1, the digital comparison function will continue to work until GO/DONE is cleared to 0. This is different from the working method of analog-to-digital conversion. The ADC module with digital comparison function can work in Idle mode, and the ADC interrupt can wake up the Idle mode. However, in Power-Down mode, the ADC module is disabled. Based on this principle, the relevant registers and setting parameters of the ADC can be reasonably configured.

　　3. Project design diagram

　　1. Hardware design block diagram

　　2. Software design block diagram

　　System overall program design flow chart:

　　Program flow chart of the location acquisition subsystem based on GPS chip:

　　GSM/GPRS communication subsystem program flow chart:

　　4. Test Results

　　The test of this system is divided into overall system test and subsystem test, please refer to the test video for details. The website is: http://pan.baidu.com/s/1i30t1e1.