1、中文 3100 字 外文资料原文 Design Of Medical Ward Call System Based On Power Line Carrier Technology I. INTRODUCTION The medical ward call system is a kind of call tools when the patient needs access to care or diagnosis, patients request can be quickly transmitted to doctors or nurses on duty. It is one of t
2、he necessary equipment to improve the level of hospital care. Currently, there are many medical ward call systems with different types and different function on the market, they are divided into two categories: the cable-type and wireless-type1. Traditional cable-type medical ward call systems tend
3、to use a centralized call system structure, power lines, data communication lines, voice communication lines transmit separated, has Line with the laying of more, high cost, installation difficulties, poor real-time, high failure rate and other shortcomings.Wireless-type medical ward call systems do
4、 not lay the line, but its reliability is poor, and radio waves can interfere with other medical instruments and equipment, most hospital do not use such wireless call system. With the development of communication technology, people have done a lot of research work for power line carrie communicatio
5、n technology. Power line carrier communications technology refers to a means of communication which uses power lines to transfer data and media signal. It loads high-frequency contains information on current, then use current transmission,then use the adapter which receives information to separate h
6、igh-frequency from the current, and transferred to a computer or telephone in order to achieve information transmission. Electricity supply network is the most popular network in the world, low voltage power lines connect to thousands of families, it can be used for data communication and informatio
7、n transmission without laying dedicated communication line and occupying the wireless channel resources2. Therefore, it has become possible that using low voltage power lines as the transmission medium, and using spread spectrum, digital encoding, single-chip control technology to achieve ward calls
8、. In this study, the power line carrier communication technology has been applied to ward call system. The entire system requires only a two-core shielded cable, through the power cord that the host provides to each extension realize two-way data communication.With low cost, simple installation, ext
9、ensive transmission lines, etc, the hospital ward has a good application prospect in practice. II. SYSTEM STRUCTURE AND WORKING PRINCIPLE The call system mainly consists of the host, extensions and power line carrier circuits, the host is installed on the ward nurse duty room, extensions were instal
10、led in the ward, a host can control multiple extensions，一 220V civil power lines is as a transmission channel, in order to achieve two- way communication between the host and the extension. The structure of system is shown in Fig. 1. The system uses a centralized power supply, supplies work power to
11、 ward extension through the two-core cable by the communicating hosts. The signal of the host to each extension through the power line carrier circuit, after 一 220 V commercial power line transmission, achieves the half- duplex data communication between the host and the extension. A communication p
12、acket consists of 8 bytes of data, the first and second byte to is the host ID, the third byte to is the command， the fourth and fifth byte is the extension address, the sixth to eighth byte to is data. The host sends command data in a broadcast, the extension analyses data after receiving communica
13、tion bag, identify whether the extension address is its address, only after confirmation the extension sends his alarm information to the host. The system uses the master-slave structure, the host sounds and light alarms when hospital beds have call requested,and show the occurrencing call extension
14、 number of beds on the display.When the extension requires a request call, press the request button, the corresponding request message is sent to the host, call to the Duty Office, when the host returns the correct information, lights the call indicator. III. DESIGN OF SYSTEM HARDWARE A. Selection o
15、f the main circuit chip The power line carrier communication refers to the process of using a dedicated modem chips for data modulation and being loaded into the power line frequency of 50Hz to send out, and then receiving, demodulating, restoring data. Here,we choose power line modulation chip PL21
16、02 designed By XiaoCheng star company. PL2102 is a half- duplex asynchronous modem chip designed for power line carrier communication network3, supplied by single 5V power,connected to an external microprocessor through a standard IC interface, coupled to the power line with an external interface ci
17、rcuit. In addition to having basic communication control function, PL2102 also build in five kinds of commonly used functional circuits: digital frequency correction real clock circuit, 32 bytes SRAM, voltage monitoring, watchdog timer and reset circuit. Among them, the real-time clock and 32 bytes
18、SRAM can continue to work by the 3 V spare battery in the case of main power loss. The watchdog timer is used to protect applications against hardware or software errors,by generating a reset signal to ensure a successful reset. As PL2102 uses direct sequence spread spectrum, digital signal processi
19、ng, direct digital frequency synthesis and other advanced technologies, and uses the large-scale digital/analog mixed 0.35 m CMOS fabrication. So it has a superior performance in the anti 一 jamming and anti-fading performance and the cost performance of similar products at home and abroad, and so on
20、. AT89C52 is a low voltage, high-performance CMOS 8- bit MCU produced by the U.S. ATMEL corporation. It contains 8KB Flash read-only program memory can be repeatedly erased and 256B random access data memory (RAM). The chip is produced by high-density, nonvolatile memory technology of ATMEL corporat
21、ion, it is compatible with standard MCS-51 instruction set and 8052 Product pin. AT89C52 has 40 pins, 32 external bi-directional input/ output (I /O) ports and includes two external interrupt ports, three 16-bit programmable timer counter, two full-duplex serial communication ports, two write port l
22、ine. AT89C52 can be programmed according to conventional methods, can also be programmed online. It makes the general-purpose microprocessor and Flash memory together. In particular, the Flash memory can be repeatedly erased can effectively reduce the development costs4. Based on the above factors,
23、the host and extension control chip select AT89C52, can fully meet various needs of the system. B. Design of the power line carrier circuit The power line carrier circuit mainly includes a power line coupling circuit, the signal receiving circuit and signal transmitting circuit, it sends and receive
24、s the power line carrier signal. Schematic is shown in Fig. 2. The coupled circuit that is transformer-coupled coil TZ in Fig. 2, is the output and input channel for the carrier signal， and play the role of isolation frequency 220V/50Hz5. Signal receiving circuit: The coupling coil couples the carri
25、er signal received form the power line to both ends at D1, Clamped by D1, the starting level of the signal is at a fixed value, and to prevent excessive inrush current. C2, C3 and L2 constitute a parallel resonant circuit whose resonant frequency is 120 kHz. The 120 kHz signal in the input weak sign
26、al is selected frequency and amplified in order to improve the sensitivity of the received signal. It is sent to the SIGin port of chip PL2102, the carrier signal received by PL2102 demodulates the data bit information after being treatment in-house, the data bit information is output to the host an
27、d extension control chip by RXD TXD port, meanwhile, HEAD sync outputs low level.Signal transmitting circuit: It includes the power amplifier, the filter shaping circuit and the composite pipe complementary symmetry power amplifier circuit comprised of V1, V2, V3, and V4. It amplifies the power of t
28、he carrier modulation signal outputted by PL2102s PSK OUT port. It is added to the coupling coil after filtering integer by C1 and L1, and is fed into the power line through the coupling coil. The carrier modulation signal outputted by PL2102 is amplified through the power amplifier circuit, filter
29、out signal noise and false signal. Capacitor C1, inductor L1 (18uH/200mA) of the integral filter circuit are used to adjust the emission current and waveform, reducing C1 and increasing L1 will reduce the emission current and improve the waveform. Conversely, it will increase the emission current an
30、d waveform distortion. As the coil load capacity is a fixed value, adjusting C1 and L1 will affect the transmission power and their power of the coil. Meanwhile, the emission voltage VHH affects size of the transmitted power, following the launch voltage drop, transmit power has declined, the higher
31、 the voltage is, the greater the transistors own power consumption is. This emission voltage is typically chosen between lOV 一18V 6. C.Design of the extension circuit The extension includes MCU AT89C52, power line modulation chip PL2102 and some peripheral circuits. Schematic is shown in Fig. 3. Eig
32、ht request button switches are connected to the port PO of the MCU AT89C52, when a button is pressed, the input state of the port PO corresponding to this button is 0. When the MCU confirms that the host calls its address, it will scan 8-bit I /O port status of port P0, once a key is pressed, the re
33、quest information corresponding to this button will immediately send to the host, and wait for the host to confirm. When the correct information is returned, the host drives the corresponding LED indicators display via P2 port to indicate that a request signal sent successfully. Eight button switche
34、s for request are numbered, each switch represents a kind of information for request, which can be defined by users 7. P1.0 and RESET port of the MCU AT89C52 connect the backup power and power-down protection circuit in order to ensure that the system can work properly when power failure occurs. If
35、the system has detected an imminent loss of power signal, the signal through an external interrupt INTO requests interrupt to the host. The host responses to an interrupt and sends the relevant data into the RAM to store, then write 0 into P1.0, the low level on P1.0 pin triggers 555 timer,the 555 t
36、imer output pulse depends on R, C and VCC. If the timer 555 end timer, VCC is still normal, this shows that the imminent loss of power signal is the wrong alarm signal, the 555 output pulse is added to RESET and the host re-operation after reset. If the 555 timer end timing,VCC is really lower, the
37、555 timer outputs high level triggered by the P1.0 low level, and adds to RESET for standby power until VCC has returned to normal, then keep a positive pulse width time determined by the R, C. The appropriate R, C value Should be selected in order to have enough power on reset time after the main power supply VCC Returns to normal, then make the host resume normal operation after reliable reset. The AT89C52 clock uses on- chip
