Ward Calling System Based on Low Voltage Power Line Carrier Technology

In recent years, with the development of communication technology, people have done a lot of research on power line carrier communication. The power supply network is extensive, and low-voltage power lines connect thousands of households, forming the most popular network. It is used for data communication and transmission of various information, without occupying wireless channel resources or laying dedicated communication lines. It saves labor, money, and maintenance, and has broad application prospects.

Traditional ward call systems are generally wired, which is not only cumbersome to install and maintain, but also has low utilization and poor real-time performance. Although wireless call systems do not have wiring problems, they have poor reliability and radio waves can interfere with other medical equipment. Currently, most hospitals do not use wireless call systems.

With the development of power line carrier technology, it is possible to use low voltage power line as transmission medium and adopt spread spectrum, digital coding, single chip control and other technologies to realize ward calling. This paper designs a ward calling system using power line carrier technology.

1 Basic requirements of ward call system

Clinical help calls are an important means of transmitting clinical information. The ward call system is an emergency call tool for patients to request doctors or nurses on duty for diagnosis or care. It can quickly transmit patients' requests to doctors or nurses on duty and leave accurate and complete records on the monitoring center computer in the duty room. It is one of the necessary equipment to improve the nursing level of hospitals and wards. The quality of the call system is directly related to the safety of patients and has always been widely valued by major hospitals. It requires timeliness, accuracy, reliability, simplicity, feasibility and promotion. The bed call system designed with power line carrier communication technology, single-chip multi-machine communication and computer monitoring management technology has the functions of calling, ringing, display queuing, priority setting, storage record, etc., which meets the hospital's ward management and nursing requirements.

2. Design of ward call system

2.1 System composition and working principle

The ward call system consists of several call sources (usually one for each bed), a modulation and demodulation carrier module, a coupling circuit and a monitoring system, as shown in Figure 1. When the call source has a call signal, there will be a corresponding sound and light call signal indication on the monitoring system, and the call number can be displayed. If the parallel bus expansion method is adopted, the wiring between hundreds of call sources and the host is very complicated. Therefore, this system uses the serial communication function of the single-chip microcomputer to make the signal between the host and each slave pass through the power carrier modulation and demodulation module, and transmit through the ~220V civil power line to realize two-way data transmission between the host and the slave.

The system adopts a master-slave structure. The monitoring system (host) is placed in the doctor's duty room (it can be connected to the computer through the interface circuit to form a monitoring center). When the bed has a call request, an audible and visual alarm is issued, and the location of the bed is displayed on the display. The call source (slave) is placed in the ward. When the patient has a call request, press the request button to call the duty room and light up the call indicator. The host and slave are connected together through a power line. When the host and slave communicate, the host sends address information to each slave in turn. Each slave receives the address information sent by the host. If it is the same as its own address, it sends its own alarm information to the host. If there is no alarm information, it sends a blank number (00) to the host.

2.2 Introduction to SC1128 spread spectrum communication chip and transceiver circuit

The SC1128 chip is a special spread spectrum modulator/demodulator circuit developed for the power line carrier communication market. Due to the use of new technologies such as direct sequence spread spectrum, digital signal processing, and direct digital frequency synthesis, this circuit has strong anti-interference and anti-attenuation performance in power line communication. The SC1128 chip integrates functions such as spread spectrum/despreading, modulation/demodulation, D/A conversion and A/D conversion, built-in electronic meter, output drive, input signal amplification, watchdog, working voltage detection, and serial communication with the microcontroller (MCU). This chip can reduce system costs and improve system functions in small multi-functional application systems.

The block diagram of the transceiver circuit composed of the SC1128 chip is shown in Figure 2. The signal enters the SC1128 chip from the power line through the coupler, bandpass filter and preamplifier. After processing, it is sent to the power line through the power amplifier and coupler to complete the transmission and reception of the signal on the power line. Frame 1 is a coupling coil, which can couple the signal transmitted in frame 3 to the power line; it can also couple the signal received on the power line to frame 2. Frame 2 is the pre-stage receiving circuit, which filters and amplifies the received signal and sends it to the first-stage operational amplifier (pin 13) of SC1128 for processing. Frame 3 is a power amplifier, which amplifies the phase modulation signal sent from pin 24 of SC1128 and sends it to the power line through the coupling coil. Frame 4 is the internal analog signal processing circuit of SC1128, which includes a three-stage operational amplifier, and the gain of the first-stage operational amplifier is adjustable.

2.3 Design of call source circuit

The call source consists of an 8051 microcontroller (slave), an SC1128 spread spectrum communication chip and some peripheral circuits, as shown in Figure 3. Eight request button switches are connected to the P0 port of the 8051 microcontroller. When a button is pressed, the input state of the P0 port corresponding to the button is 0. When the microcontroller determines that the host calls the address of the machine, it scans the 8-bit I/O port state on the P0 port. Once a key is pressed, the request information corresponding to the P0 port is immediately sent to the host and waits for the host's confirmation. When the host returns the correct information, the corresponding LED indicator light is driven by the P2 port to indicate that the request signal is sent successfully. The eight request button switches are numbered separately, and each switch represents a request information, which is defined by the user.

The P1.0 and RST/VPD ports of the 8051 microcontroller are connected to the backup power supply and power-off protection circuit to ensure that the system can be used normally when a power failure such as a power outage occurs. If the system has detected the "power failure is about to occur" signal, the signal will request an interrupt from the host through the external interrupt INT0. The host responds to the interrupt and sends the relevant data to the internal RAM for storage, and then writes "0" to P1.0. The low level on the P1.0 pin triggers the 555 timer, and the output pulse of the 555 timer depends on R, C and Vcc. If the 555 timer ends the timing and Vcc is still normal, it indicates that the "power failure is about to occur" signal is a wrong alarm signal, then the positive pulse output by 555 is added to RST/VPD to reset the host and start to operate again; if RST/VPD does become low at the end of the 555 timing, the 555 timer outputs a high level under the low level trigger of P1.0 and adds it to RST/VPD as a backup power supply until Vcc returns to normal, and then maintains a positive pulse width time determined by R and C. Appropriate R and C values ​​should be selected so that after the main power supply Vcc returns to normal, there is enough power-on reset time to allow the host to reliably reset and resume normal operation. The clock of 8051 uses an internal clock oscillation mode, and a quartz crystal (6MHz) and an oscillation capacitor are connected to the XTAL1 and XTAL2 pins. The serial port RXD (P3.0) and TXD (P3.1) communicate with the host through the SC1128 chip and the power line. The call source interrupt program flow chart is shown in Figure 4.

2.4 Monitoring system design

The monitoring system consists of an 8051 single-chip microcomputer (host), a display device, an alarm circuit, an SC1128 chip, and some peripheral circuits, as shown in Figure 5. The three I/O lines of the 8051 single-chip microcomputer P0 port provide the clock signal, enable signal, and serial data required by MC14499. MC14499 drives and controls four LED eight-segment displays. The LED digital tube displays the bed number and alarm type of the patient who issued the alarm. Among them, the first three LEDs indicate the bed number, and the last one indicates the alarm type. The P2.0 port drives the alarm field sounder through a NOT gate. The host has a button key K, which is directly connected to INT0. K is used to cancel the alarm sound and the alarm source indicated by the LED digital tube. The backup power supply, protection circuit, and clock oscillation mode used in this circuit are the same as those of the call source circuit. The monitoring system program flow chart is shown in Figure 6.

2.5 Software Design of Ward Call Management System

The above circuit combinations can complete the ward call function. In order to improve the system and combine the call system with the bed information management, the ward call management system software is designed to form a ward monitoring center composed of a computer and corresponding interface circuits. The call information is processed by the microprocessor and input into the computer through the interface circuit, and then the call information and patient information are managed by the computer software. Here we only introduce the ward call management system software based on POWER BUIDER9.0 as follows:

This system has a protection function. Non-management personnel cannot enter the system to obtain information. Only by obtaining the password can they enter the information interface of the system. The login interface is shown in Figure 7.

The system has the functions of adding, editing, querying, deleting, flipping and exiting. After the correct password is detected, the system enters the management interface (as shown in Figure 8), which includes the management of basic patient information, display, classification and storage query of call information, etc.

Patient basic information management is to establish patient data information in the database, which is composed of tables. Tables are a method of storing organized data in the database. Tables have a pre-defined structure and store data that conforms to this structure.

The host of this system adopts the query mode, and the slave adopts the interrupt mode. The system has the following characteristics:

(1) When the address code sent by the monitoring system received by the call source is consistent with the address code of the local machine, the alarm status data of the alarm point is transmitted to the monitoring system; if they are different, no response is given. The single-chip microcomputer continuously conducts patrol inspections on the detection points, ensuring that only one call source sends an alarm signal at a certain time, solving the channel contention problem and truly realizing multi-way calls.

(2) This system uses the SC1128 chip with modulation function and a communication network formed by power lines. It has the characteristics of simple structure, low cost, flexible and reliable working mode, and strong anti-interference ability.

(3) This system uses the information monitoring management system software designed by POWER BUIDER9.0, which has the characteristics of user-friendly interface, strong confidentiality and ease of use. Operators can master it after short-term training.

In short, compared with other existing call systems, this call system is reliable, simple and practical, and is suitable for use in hospitals of all levels and types. Especially for hospitals that have already been built and need to add a call system, the ward call system based on power lines should be the first choice.