A ZigBee wireless sensor network system supporting body temperature and pulse monitoring is proposed. The node device based on JN5139 microcontroller is used in the sensor terminal, wireless router and base station. The multi-channel temperature and pulse parameters measured in the field are collected periodically through the network, and the computer is used for centralized storage and management. The system has the characteristics of high precision, good connectivity, strong scalability, and low power consumption.
Body temperature and pulse are important physiological indicators reflecting the health status of the human body. Continuous monitoring of these physiological indicators of patients can provide an important basis for the correct diagnosis and treatment of diseases. With the development of sensor technology, embedded computing technology and wireless communication technology, the vital sign monitoring system based on wireless sensor network has received more and more attention. Among them, the system based on the common radio frequency chip and the custom transmission protocol has the advantages of simple implementation and low cost, and the disadvantages are low reliability and poor versatility; the system data transmission rate based on the Bluetooth protocol is high, but the action distance is short. High power consumption and weak networking capability; ZigBee is a system based on the Low-Rate Wireless Personal Net-work (LR-WPAN) protocol specification based on the IEEE 802.15.4 communication standard. It has the advantages of low complexity, low power consumption, high reliability, strong networking capability, etc., and has become a hot research topic in this field.
This paper proposes a ZigBee wireless sensor network system that supports body temperature and pulse monitoring. It can collect the measured multi-channel temperature and pulse parameters through the network at a time, and use the computer for centralized storage and management, which improves the efficiency and quality of disease monitoring. The system has the advantages of high reliability, high scalability, low power consumption and low cost.
1 Overall structure of the monitoring systemThe monitoring system includes three types of node devices: a sensor terminal, a wireless router and a base station, and constitutes a ZigBee mesh wireless sensor network in a self-organizing manner, as shown in FIG. The sensor terminal is responsible for detecting body temperature and pulse, and the detection result is transmitted to the base station through the respective parent node router. The base station stores and displays the received data by means of the upper monitoring software, and can display the network structure and the current state of the device according to the user's needs, set the sampling period and the alarm threshold, and output a record report and a historical curve reflecting the change of the condition.
The hardware implementation scheme of the ZigBee node device is mainly divided into two categories: one is to separate the RF transceiver from the microcontroller, and each uses one chip, and the user is based on the device class (Coordin-ator, Router, End Device) and functions. Separate selection to achieve the best match; the other is to integrate the two on a single chip, which can simplify the hardware design of the device and improve the hardware reliability of the system.
JN5139 is Jennic's second generation IEEE 802.15.4/ZigBee single-chip wireless microcontroller with 32-bit RISC CPU, 2.4GHz IEEE 802.15.4 RF transceiver, 192 KB ROM, 96 KBRAM And rich interface resources such as parallel port, serial port, timer, A/D, D/A. In order to improve the electromagnetic compatibility of products, JN5139 chip, 16 MHz crystal oscillator, 128 KB serial flash memory, ceramic antenna and other components are integrated into a common module, with its core, with corresponding peripherals, protocol stack and application code. Different types of ZigBee node devices can be implemented.
2.2 Sensor terminalAs shown in Figure 2, the sensor terminal consists of the JN5139 minimum system, body temperature detection circuit, and pulse detection circuit, and is powered by a 3.6 V NiMH battery. The minimum system includes the JN5139 module, reset components R1 and C1, status indicator D1, and program download interface j1. After the power-on reset, the Bootloader in the internal ROM of the JN5139 automatically detects the MISO pin level. If it is high, the program code in the off-chip serial flash is directly loaded into the on-chip RAM; if it is low, it enters the programming state, downloads the latest code on the PC through serial port 0, and writes it to the serial Flash.
The body temperature detecting circuit is composed of a high-precision NTC thermistor RT and precision resistors R3 to R5. JN5139 controls the temperature measurement circuit by making DI01 output low level, and uses three 12-bit A/D conversion channels to measure the potential of three points respectively, find the resistance value of the thermistor, and then use the thermistor RT relationship. The table and the piecewise linearization formula give the corresponding temperatures.
The pulse detection circuit includes a photoelectric sensor and its signal conditioning circuit, as shown in FIG. The photoelectric sensor is composed of a red light emitting tube D1 and a phototransistor Q1, and the two are oppositely mounted in the light shielding finger sleeve. When measuring the pulse, part of the emitted light passes through the fingertip and illuminates the light-receiving surface of the phototransistor. The transmitted light intensity shows a slight change with the pulse fluctuation. After the photo-electrical conversion of the phototransistor, the output is superimposed with the superimposed alternating current and the weak alternating current. Voltage signal. The signal is subjected to DC blocking, low-pass filtering and amplification processing, and becomes an analog pulse signal with a peak value close to Vcc/2, and then A/D conversion, digital filtering and period determination are performed by JN5139, and finally the pulse rate value in min is obtained. . In order to solve the problem that the pulse output signal is saturated or too small to solve the individual difference, the working current of the transmitting tube is automatically adjusted by the JN5139 through the D/A converter.
The wireless router is mainly responsible for data forwarding, and does not undertake data collection tasks. Therefore, its hardware only involves the JN5139 minimum system (powered by 3.6 V DC power supply), and no additional peripherals are required.
The base station adopts the upper and lower position machine structure, as shown in FIG. The lower computer as the network coordinator is the JN5139 minimum system, and the upper computer adopts the PC, and the two communicate through the asynchronous serial port (the baud rate is 115.2 kbps). Both the JN5139 minimum system and the MAX232 level shifter are powered by a 3.6 V blind current supply.
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