I. Design Background 1. Introduction to Remote Automatic Meter Reading: A remote automatic meter reading system is a system that can automatically collect and record the electricity consumption of customers in a power system, and automatically transmit the recorded data and customer information back to the power management center through a channel using a certain communication method. The system then processes the data and automatically completes the electricity billing and management functions for electricity customers in the power system. 2. Low-voltage Power Line Carrier Communication: Low-voltage power line carrier communication uses low-voltage power lines as the communication medium. Communication between the user terminal's electricity consumption data and the concentrator is accomplished through power line carrier technology. 3. Composition of a Remote Automatic Meter Reading System Based on Power Line Carrier Communication: The system mainly consists of a data acquisition terminal that collects electricity information from user electricity meters, a concentrator, a channel, and a master station. The concentrator is installed near the transmission transformer and is used to collect data from ordinary electricity meters collected by the data acquisition terminal. It then transmits the data to the meter reading center using various channels such as dial-up and the Internet, and transmits commands from the meter reading center to the data acquisition terminal. 4. Advantages of Remote Meter Reading with Low-voltage Power Line Carrier Communication: Using existing power lines as a communication medium for remote meter reading and real-time monitoring is a high-tech approach. Its successful research can not only replace manual daily meter reading work, improve work efficiency, reduce human error, and strengthen user management, but also achieve full automation of remote monitoring and management work. It is the development trend of power sector to realize remote automatic meter reading and has broad application prospects. With its low cost, it has become the preferred technology in the market. Moreover, the development of communication technology, computer technology and intelligent control has created conditions for power line carrier meter reading. 5. Technical difficulties in realizing remote meter reading system of low voltage power line carrier: The communication distance and communication quality of low voltage power line carrier communication are the difficulties in realizing the system. The main factors affecting the transmission quality of power line carrier are: the impedance characteristics of the power network, the attenuation characteristics and noise interference. The former two restrict the transmission distance of the signal, and the latter determines the quality of data transmission. This is determined by the transmission characteristics of the voltage power line itself. (1) The interference and attenuation of the line are very large. Many electrical devices are randomly connected to the low voltage power line, some of which will generate great interference. Such as switching power supply, frequency conversion equipment, etc. Some may have a great attenuation of the carrier signal. (2) The impedance of the line changes over time. Due to the high randomness of the connection of electrical equipment on the low-voltage power line, and each electrical equipment is an attenuation source on the line, the impedance on the line changes dynamically. This makes it impossible for the impedance of the equipment on the line to match the line when transmitting data, resulting in signal reflection and signal weakening injected into the line, which directly affects the transmission quality. (3) The transmission quality changes over time. Due to interference, attenuation and line impedance are dynamic, the transmission quality varies greatly at different times. (4) There is uncertainty in point-to-point transmission. For two devices on a low-voltage power line, the success or failure of their transmission changes over time. During the off-peak hours, the modulated signal can be transmitted far, and the two devices can communicate directly. However, during the peak hours, the modulated signal is quickly attenuated and subjected to strong interference, and the two devices may not be able to communicate directly. II. Design Objectives 1. Realize the basic functions of the concentrator The basic functions of the concentrator are as follows: a) Metering function, collecting user electricity data collected by the collection terminal. b) Setting function, including meter reading time setting and fixed relay setting. c) Communication function, the concentrator receives data downloaded from the host computer. d) Data processing, including data storage and freezing. e) Time synchronization function, allowing system time synchronization via a host computer to adjust time errors. f) Relay function, increasing transmission distance. 2. Introduce the real-time operating system μC/OS-II to enhance the system's real-time performance, maintainability, and scalability. General embedded software system designs typically employ a foreground/background design approach. The foreground program is a real-time interrupt program used to handle asynchronous events. The background program is an infinite loop, calling corresponding functions to complete the corresponding operations. The system's timeliness in processing information is worse than practically achievable. When the system has many tasks, the traditional method to achieve real-time operation of multiple tasks is to use multi-level nesting to achieve parallel processing of multiple tasks, increasing the difficulty of software development and reducing the reliability of the software system; information exchange between tasks is difficult. The foreground/background design method generally uses global variables to solve communication problems, which is prone to errors in complex situations, and deadlocks can occur if calls are not made correctly. 3. Employ embedded Internet technology to achieve communication between the concentrator and the master station through a network interface. With the development of network technology, Internet technology has become an important channel for information exchange. Implementing a network interface in the system provides users with a more user-friendly operating interface. 4. Implement an automatic relay algorithm to overcome the shortcomings of fixed relay algorithms. Traditional methods for solving power line communication distance issues use fixed relay algorithms. Fixed relay algorithms have significant drawbacks in system expansion and maintenance. We propose to implement an automatic relay algorithm that automatically relays data when power communication cannot be reliably completed, thereby increasing the success rate of first-time meter reading. III. Design Block Diagram The concentrator itself consists of a main control unit, data storage unit, clock unit, carrier communication unit, and data transmission communication unit. The main control unit uses the STR912FW44ARM chip and is mainly responsible for monitoring the entire system, communicating with the host computer's data acquisition terminal, data storage, and system configuration functions. The telephone modem unit mainly utilizes the public telephone network (PTN) to communicate with the concentrator. The host computer uses the PTN to collect user data, perform system time synchronization, and configure system settings. The power modem and power line interface unit complete the communication function between the concentrator and the acquisition terminal. The power modem unit completes the modulation and demodulation functions of user data. We use the ST7538 power modem chip manufactured by STMicroelectronics as the modem; the power line interface unit mainly completes the coupling of the modulated data with the power line. The infrared module unit is mainly used for the initial configuration function of the system. When the remote communication between the host computer and the concentrator is blocked, it allows the staff to complete data collection and other functions through the infrared module. The network interface module is mainly used to enable the host computer to communicate with the concentrator through the public Internet. It adopts embedded WEB technology to provide users with a more user-friendly operating interface. IV. Design and Implementation To improve the development progress of the project, we use the Embest STR912 development board manufactured by Embest as the main control board for development and debugging. We use the network interface and serial port interface modules on the development board for debugging and development. We implemented the power modem module, telephone modem module and infrared module of the system on the experimental board. We built a simple development platform using the development board and the experimental board to design and verify the system functions. Currently, we are debugging the communication between the power line module on the main control board and the experimental board.