Design scheme of unattended ward monitoring system based on radio frequency technology
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The three physiological parameters of body temperature, heart rate and respiratory rate are the most important and basic vital signs of the human body. Monitoring multiple vital signs of the injured and sick is conducive to timely and effective treatment. However, most of the current monitoring systems in my country are manual bedside monitoring and wired bedside monitoring. The former wastes manpower and has low reliability; The latter is costly and difficult to wire. There is an urgent need for a monitoring method that can reliably monitor patients and save manpower and material resources. The unattended ward monitoring system introduced in this article is designed to meet this need. The system uses biomedical sensors to detect the patient’s body temperature, heart rate (pulse), respiratory rate and other physiological parameters in real time, and the detected data is wireless The radio frequency module is sent to the monitoring center to monitor the patient’s physical condition in real time, which not only saves manpower and material resources, but also improves the hospital’s medical service quality and hospital management level, and is easy to install, low cost, and simple to use.
1 System composition and working principle
The unattended ward monitoring system is mainly composed of a data collector, a wireless radio frequency module SM50, a monitoring computer and other parts. The schematic diagram of the structure is shown in Figure 1.
The data collector worn on the patient integrates a variety of biomedical sensors such as heart rate sensors, respiratory rate sensors, and temperature sensors. It can monitor the patient’s heart rate, respiratory rate, body temperature and other physiological parameters in real time, and record them through ferroelectric memory The data collection time is then sent to the central ward monitoring computer in real time through the wireless radio frequency module SM50. If an indicator of the data sent by a certain ward is abnormal, the system will alarm to remind the monitoring personnel to take timely treatment measures for the relevant patient, so as to treat the patient in a timely manner, ensuring the safety of the patient and improving the monitoring efficiency. Of course, the monitoring personnel can also index the monitoring computer database, analyze the physiological parameters of certain patients in a targeted manner, change the treatment methods in time or take effective prevention and control of the disease in advance, thereby guaranteeing the patients to the greatest extent Rights.
2 System hardware design
2. A data collector hardware design
The data collector is worn on the patient and mainly completes the functions of collecting, processing and storing the physiological parameters of the patient. It is composed of a sensor circuit, a microprocessor, and a ferroelectric memory. The sensors include temperature sensor DSl8820, HK-2000A integrated pulse sensor, HXB-2 piezoelectric respiration sensor and other sensors to be expanded. The microprocessor uses PLILIPS’s high-speed, low-power, 8-bit FLASH microcontroller LPC932, and iron The electric memory chooses FM31256 with integrated clock circuit of RAMTRON Company. The electrical schematic diagram of the data collector is shown as in Fig. 2.
Install the digital temperature sensor DS18B20, HK-2000A integrated pulse sensor and HXB-2 piezoelectric breathing sensor connected to the data collector to the relevant parts of the patient’s body as required, and then turn on the data collector to start collecting the patient The physical sign parameters of the patient are stored in the ferroelectric memory FM31256 together with the time of data collection. At the same time, the radio frequency module SM50 is activated to send out the bed number, collection time and monitoring data in real time. The red indicator D3 flashes to indicate successful data transmission. When the voltage of the power supply battery is insufficient, the microcontroller LPC932 will be relatively interrupted. At this time, the yellow indicator light D4 will flash to indicate to remind the staff to replace the battery, which improves the working reliability of the data collector.
2.2 The use of wireless radio frequency module SM50
Shanghai Sangbo Electronic Technology Co., Ltd. provides SM50 module to provide two serial ports, COM1 (Pin3, Pin4 of CON1) is fixed to TLL level UART serial port; COM2 (Pin6, Pin7 of CON1) can pass the D bit of jumper J2 To choose the interface mode, including RS 485 and RS 232. In this design, the TTL level is between the data collector and SM50, and the RS 232 is between the monitoring computer and SM50. The SM50 module provides 1 200 b/s, 2 400 b/s, 4 800 b/s, 9 600 b/s, 19 200 b/s and other interface baud rates. The baud rate can be set by changing the J2 jumper B, C state to determine. The operating voltage of the module is +3.3 ~ +5.5 V. In order to effectively save power consumption, the module can be set to a sleep state. The biggest advantage of using SM50 is micro power consumption (no harm to human body, especially infants).
3 Design of communication protocol
In the wireless communication system, due to the influence of factors such as power supply, space noise, and transmission path, the data transmission process is easily interfered, causing communication failure. Therefore, it is necessary to design a transmission protocol to ensure that it is on this unreliable physical link Establish a reliable data connection. In this system, the data collector and the monitoring computer are a simple multi-point-to-point communication.
3.1 Baud rate setting and communication mode selection
Taking into account the characteristics of the wireless radio module SM50 itself and taking into account the speed and stability of data communication, this design uses 9 600 b/s. Since the communication is a many-to-one relationship, the serial port chooses working mode 3.
3.2 Determination of data verification method
When using wireless communication technology to transmit data, it is easy to encounter interference, which will change the transmitted data and cause transmission errors. Taking into account the actual requirements of the system, this design uses an 8-bit CRC (cyclic redundancy check) check method.
The calculation of the CRC checksum is a cyclic calculation. From a mathematical point of view, the CRC checksum uses a generator polynomial (algorithm rule) to remove a polynomial (represented by a data block), and the CRC check is the remainder after the division. CRC check is to add some check bits to a data block to be transmitted. These check bits (CRC check bits) are calculated by the data block and transmitted together with the data block. At the receiving end, the CRC checksum is recalculated according to the specified algorithm for the received data block, so that it can be judged whether there is an error in the data transmission process.
The CRC check subroutine in this system is as follows:
3.3 Coding of communication data
To ensure the reliability and accuracy of data transmission, the data frame format used in this design is shown in Table 1. Among them, the first two bytes are the initial synchronization signal, and the address code occupies one byte (0～255), which is used to mark different bed numbers; the data to be sent includes: heart rate (1 B), respiratory rate (1 B), Body temperature (2 B) and acquisition time (7 B); the check code is an 8-bit CRC check code. The transmission sequence is: heart rate, respiration rate, body temperature (high position first, low position behind), acquisition time (sequence: second, minute, hour, day, month, year); when the response command is sent, the data to be sent is 2 0xcc or 0xBB of B.
4 Computer software system design
The visual programming language Visual Basic is used on the Windows operating platform: Database Server of the design system, Visual Basic is an object-oriented visual rapid application development tool, with powerful functions, friendly interface, easy to use and fast code execution. The system has functions such as data indexing, system settings, and reports. Depending on the patient’s condition, doctors can formulate different monitoring standards. Figure 3 is a screenshot of the system operation interface (including some experimental data).
5 Conclusion
The unattended ward monitoring system based on radio frequency technology omits complicated wiring, convenient installation, simple operation, reliable work, low failure rate, and easy maintenance. Once it enters the practical stage, it will save the hospital’s operating costs and improve the quality of medical services. The management level will ultimately benefit patients and medical staff, which is of great significance for accelerating the process of intelligent construction of hospitals in our country.
Excerpt from the Electronic Engineering Special Collection
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