Abstract: This paper introduces the design of a remote automatic meter reading module using LonWorks bus power line data transmission, and the structure and function of a smart community meter reading system composed of the automatic meter reading module. Keywords: LonWorks bus; microcontroller; remote meter reading Introduction Currently, China commonly uses manual meter reading and billing for water, gas, and electricity meters, which brings many inconveniences to both users and meter readers. With the development of technology, especially the emergence of smart communities and high-rise residential communities, traditional meter reading methods can no longer meet the needs of residents. To effectively solve the many drawbacks of manual meter reading and billing and improve work efficiency, an automatic meter reading system is the best solution. Due to its excellent characteristics, LonWorks bus technology has become the de facto recommended standard for fieldbus. LonWorks network topology has great flexibility, providing various typical topologies such as bus, star, ring, and hybrid topologies through multiple transceivers. Network information between different channels is bridged by transceivers. Using transceivers not only enables data transmission between different communication media but also improves network response time and security performance. The remote automatic meter reading module developed by Ouyu Company is based on LonWorks technology and uses power line data transmission. It can automatically record readings of residents' gas, water, and electricity meters and has network connectivity. Data can be remotely queried and recorded on the community's management computer or via the local telephone network. I. LonWorks Automatic Meter Reading Module (Node) and System Working Principle Each measurement and control unit on the LonWorks network is called a LonWorks intelligent node. Each intelligent node uses a LonWorks main control module. The LonWorks main control module is the basic building block of the intelligent node. It uses a Neuron chip as its core and includes a transceiver, address decoding circuit, reset circuit, crystal oscillator circuit, and EPROM. The main control module completes data transmission of the LonTalk protocol through firmware and performs various user-defined calculations, I/O event processing, and network packet processing functions through event scheduling. A schematic diagram of a LonWorks node is shown in Figure 1. The main control module is used for communication and control: the 89C51 microcontroller processes and drives input/output data. In the meter reading module, it mainly counts pulse input signals and completes data transmission with the main control module. The transceiver in the main control module connects nodes to the network. Different communication media require different transceivers: in the meter reading module, the FTT-10A transceiver, suitable for twisted-pair media, or the PLT-22 transceiver, suitable for power line communication media, can be used. The automatic meter reading system is based on LonWorks fieldbus technology. The system consists of the following parts: computer, meter reading management software, data concentrator, meter reading node modules, repeaters, modem, water, electricity, and gas pulse meters, etc. The meter reading module collects the pulse output signals from each pulse meter in real time and accumulates the pulse count in the meter reading module's RAM. Based on the set time intervals and the current time, the collected data is accumulated into different time periods to achieve time-segmented counting. The meter reading module's memory has a power-off protection function to prevent the loss of pulse accumulation values ​​in case of power failure. The data concentrator has a large-capacity memory capable of storing data from 200 meter reading modules. The concentrator repeatedly polls and collects data from each meter reading module, storing it in its corresponding memory. The concentrator automatically filters illegal data and handles communication anomalies accordingly, ensuring that a copy of the data from all meter reading modules in the network is stored in the concentrator. The automatic meter reading system is characterized by numerous and dispersed data acquisition modules, relatively low real-time data transmission requirements, and the requirement that each transmitted and received data be error-free. When the host computer collects data, it can directly send the data stored in the concentrator back to the computer, without needing to directly read the meter reading data from the meter reading modules. Because data communication does not require protocol conversion, the communication speed is fast, and even in the event of communication anomalies in the LonWorks network, data can be quickly sent back to the host. The LonWorks neuron chip program is divided into two parts: an application program and a network image. The application program determines the module's functionality; the network image determines the module's network connectivity with other modules. Two installation methods are available: pre-installation and field installation. Pre-installation method: LonWorks control network has rich functionality, but for a specific meter reading system, only a portion of its functions are used, and these functions are relatively fixed. The network connections between modules can be predetermined. Therefore, the parameters configured using LonMake are changed to be configured via host commands. All meter reading modules are pre-installed with the necessary programs and configurations, and are labeled with their module numbers before leaving the factory. This eliminates the need for on-site installation using LonWorks software. With pre-installation, users can install the meter reading system without needing LonWorks knowledge. Field installation method: This method requires installers to create network images for each module on-site using LonWorks software and download the network images to each meter reading module. This configuration is flexible; meter reading modules can share a network and exchange data with multiple LonWorks modules. On-site installation allows for full utilization of LonWorks control network functions, but it places higher demands on the engineering company, requiring a deep understanding of LonWorks networks. The design of the meter reading module needs to solve the following problems: (1) The meter reading module can adapt to various pulse meter outputs, can correctly collect pulse signals and detect abnormal situations such as open circuit or short circuit in the signal connection. (2) Solve the limitations and reliability of power line communication distance. 1. Hardware design of automatic meter reading module This module is specifically used for automatic reading of water meters, electricity meters and gas meters. Each module can directly read 24 pulse output type meters. In the pulse monitoring part, the terminal resistor matching method and A/D technology are adopted to convert pulse acquisition into the acquisition of analog quantities. Then, by analyzing its A/D sampling value, the status of the pulse meter can be identified and the continuity status of the line can be detected. The communication between the LonWorks bus main control module and 89C51 adopts the synchronous serial I/O method and uses the Neurowire master control method, that is, the main control module drives the synchronous clock input and chip select signal output, and 89C51 receives the synchronous clock input. The IO8 pin of the Neuron chip in the main control module outputs a synchronous clock; the IO9 pin is a serial data output; the IO10 pin is a serial data input; and the IO5 pin is selected as the chip select signal output. The 89C51 uses interrupt mode to transmit data and adds a check code to the protocol frame to ensure the correctness of the communication data, as shown in Figure 2. The meter reading module designed with dual CPU technology has the following functions: (1) It can simultaneously collect 24 pulse meters and support multiple input modes such as single contact, double contact, and level input; it can simultaneously support three different pulse meters. (2) It has the function of detecting broken or short-circuited pulse meter connections. (3) It can collect pulse signals with a pulse width > 10ms. (4) The module has an internal clock and can perform time-sharing billing. (5) It has a power-off protection circuit to ensure that the counting data is not lost when the power is off. (6) It downloads data from the computer, performs initial settings, and allows the computer to view various data. (7) It has a low voltage detection circuit and alarms the computer when the voltage is lower than a certain value. (8) It has a reset switch, which resets all counters before use. (9) The module can provide 12V/100mA or 5V/100mA power to the outside. (10) The power supply adopts AC220V power supply, which is convenient for users. (11) It can be connected to a battery. Using a 12V/7AH battery, it can power the module for 2 days (excluding power supply to the outside). 2. Power line communication Power line communication modulates data into a carrier signal or spread spectrum signal, and then couples it to 220V or other DC power lines, or even twisted pairs without power, through a coupler. The advantage of doing this is that it uses existing power lines for data communication, which greatly reduces the cumbersome wiring encountered in communication. LonWorks power line transceivers provide a simple and grounded way to add neuron nodes to power lines. The key to power line communication is: how to ensure reliable long-distance communication on power lines. The following problems exist in power line communication: the power line has large intermittent noise (some circuits will generate large noise when starting, stopping and running); the signal attenuates quickly; and the line impedance fluctuates. These problems make communication over power lines very difficult, and the use of the new PLT-22 power line transceiver is currently a better solution. The PLT-22 transceiver is a high-performance power line transceiver, but in practical applications, the communication distance and three-phase power line coupling problems need to be solved. The number of nodes communicating on power lines is only limited by the LonWorks network, and the communication distance is determined by signal attenuation and noise on the power line. The network structure belongs to its own topology. To extend the power line communication distance, two methods can be used: (1) enhance the output strength of the power line communication signal; (2) add repeaters to the power line. Using method (1) requires adding a power line signal amplifier PLA21. At present, this amplifier is relatively expensive, and the cost of nodes using the amplifier is also relatively high. It is only suitable for relatively important or critical nodes, such as in data concentrators; it is not suitable for use in meter reading modules. The power line communication network structure belongs to a free topology, but all lines of a certain phase are connected together on a power line network. From a communication channel logic perspective, a power line network has only one communication channel and cannot be physically separated into two independent network segments. Therefore, ordinary repeaters cannot be used to extend its communication distance. Ordinary repeaters are suitable for connecting physically unconnected networks, such as connecting power lines from two different transformers. To extend the communication distance of a single phase of the network, other measures must be taken. In this meter reading system, a soft repeater method was successfully adopted. The principle is to use a node as a repeater node. This node receives data from three designated nodes B and C on the power line, where A and B, and B and C can communicate normally, but A and C cannot. Using B as a repeater, if A wants to communicate with C, A sends a message to B, and B then sends the message to C, thus achieving communication between A and C. Based on the above description and requiring convenient system installation and configuration, the meter reading modules are divided into three different types. Each type of module can not only normally collect data from 24 pulse meters but also function as a soft repeater. Each type of module has different relay functions, the purpose of which is to prevent information packets from forming loops and causing information to be continuously transmitted on the network. Their connection relationship is shown in Figure 3. (1) The concentrator can communicate with all modules. (2) Relay 1 can transmit the information received from the concentrator to relay 2 and interrupt 3; and transmit the information received from relay 2 or relay 3 to the concentrator. (3) Relay 2 transmits the information received from the concentrator or relay 1 to relay 3; and transmits the information packets received from relay 3 to relay 1 and the concentrator. Three-phase power line communication: For the meter reading system, all meter reading modules communicate with the data concentrator, and the meter reading modules do not need to communicate with each other. Therefore, as long as one three-phase power coupler is installed in the concentrator, the other meter reading modules can be single-phase power coupled to realize the transmission of meter reading data on the three-phase line. The power line meter reading system is based on transformers. Each transformer low-voltage grid is an independent communication network, and different transformer output low-voltage networks do not communicate with each other. The system consists of a data concentrator, relay modules and meter reading modules, as shown in Figure 4. Before use, the data concentrator needs to register module numbers. Concentrator registration refers to the host computer downloading all the numbers of the meter reading modules that the concentrator needs to collect data from to the concentrator. Multiple concentrator modules can be installed on a network. When different modules are registered by the concentrator, the concentrator collects data from those different meter reading modules. This setting can be used when the number of meter reading modules in the system exceeds the number of modules the concentrator can collect data from. When the module numbers registered by the concentrator are the same, the concentrator collects data from the same meter reading module. This setting can be used for data backup. II. Automatic Meter Reading System Structure and Functions The community management center uses a PC as the management machine to realize remote meter reading and billing printing functions. A LonWorks network card - PCLTA is inserted into the computer. The computer is connected to the community's LonWorks meter reading network, and the transmission medium is power line. Each meter reading module can support up to 24 billing meters. The management computer can query the readings of any household's water meter, electricity meter, and gas meter at any time; it can also perform statistics, calculate costs, and manage payments for the monthly water, electricity, and gas consumption of users; and automatically print overdue payment notices for users with outstanding payments. Through the LonWorks bus control node, it can also remotely control the opening and closing of water, electricity, and gas, facilitating effective management of the supply of water, electricity, and gas. Combined with the corresponding management software, the system has the following functions: (1) The automatic meter reading system's meter reading module forms a two-level network, using power lines or twisted-pair cables as the transmission medium and adopting a free network topology structure. The water meter, electricity meter, and gas meter of each household in the community can be read on the management microcomputer. (2) Remote control can be implemented, allowing the three meters to be turned off or on at the management center. In the event of a disaster, the management center can turn off the gas or electricity supply on behalf of the user to reduce safety hazards; in the event of overdue payments or violations, the supply of water, electricity, and gas can be turned off through the network to strengthen the management of overdue payments and the handling of violations. (3) It has alarm functions for gas leaks, meter reading communication interruptions, sensor disconnections and short circuits, abnormal gas valve operation, and low battery voltage, and can record historical alarm data. (4) The real-time readings of each meter in the community can be queried on the management microcomputer. Conclusion In recent years, the application of LonWorks technology has developed rapidly in China, and many system integrators at home and abroad have actively participated in the development of LonWorks smart nodes. At present, LonWorks technology products have been widely used in intelligent buildings, industrial control, power automation, security and other fields. The automatic meter reading system based on LonWorks technology that we developed and produced has been successfully applied in actual projects and is operating well. The implementation of the automatic meter reading system has improved the level of intelligence in community management, improved the comfort and safety of residents and management efficiency, and brought great convenience to people's production and community management.