Abstract: This paper introduces the design of a locomotive electrical fault detection and display device. The device uses an 89C51WD single-chip microprocessor as its control core and can automatically detect and display the location of faults in the locomotive's electrical circuits. The paper describes the system composition and circuit structure of the device, and explains its hardware structure and software design. Keywords: single-chip microprocessor; diesel locomotive; electrical fault; detection ; 1. Introduction Currently, railway traction power is still mainly based on diesel locomotives. How to timely grasp the dynamic information of diesel locomotives has always been a problem that plagues on-site technicians. Due to the complex logic of the electrical circuits in diesel locomotives, fault points are numerous and widespread. Furthermore, with the increasing speed of passenger trains and heavy-load traction of freight trains, locomotives operate at full power, experiencing high temperatures, significant vibrations, and harsh working conditions for the electrical circuits, making faults unavoidable. Once a locomotive malfunctions, the driver and crew cannot inspect and handle the problem, inevitably affecting normal train operation. This paper proposes a design method for a locomotive electrical fault detection and display device. This device can automatically detect and display fault locations in the running control circuit, the main generator excitation circuit, and the exciter excitation circuit, reducing and preventing locomotive breakdowns and ensuring train safety. 2. Main technical features of the device : a. Automatically switches between detecting L and F excitation circuits based on the operating status of the excitation circuit. b. Automatically detects the running control circuit according to the direction of travel. c. Displays or processes the fault location of the detected circuit using a large-screen LCD display in a graphic and textual format. d. Fault detection uses photoelectric isolation, providing strong anti-interference capabilities. e. Automatically records the fault location and the date and time of the fault. 3. Device Composition The device system is shown in Figure 1. The entire device consists of two main parts: the main unit and the display screen. The main unit includes detection and system control circuits and is installed in the locomotive's electrical room. The display section includes two large-screen LCD displays and related buttons and control circuits, installed on the driver's control panel at both ends of the locomotive. Data and command information between the main unit and the display screen are transmitted and exchanged via an RS485 communication bus. Operators can control the device using the buttons on the display panel to perform different detection tasks or display related fault locations. [align=center] Figure 1 Device Composition[/align] 4. Hardware Design The hardware circuit of this device is shown in Figure 2, including signal detection, signal acquisition, system control processing, and display. Signals from the main monitoring points of the locomotive's electrical circuit are sampled and photoelectrically isolated before being sent to the signal acquisition interface. Under the control of the CPU, each signal is sampled in turn, and compared and analyzed according to the logical relationship of the locomotive's electrical circuit. If a problem is found, the data is saved according to the fault location, and a corresponding fault graphic code is generated to notify the display circuit for display. The display control circuit communicates bidirectionally with the system control circuit via an RS485 interface, receiving various commands from the system control circuit and displaying the detected data and graphics on the LCD screen. The buttons are processed by the CPU on the display control circuit; operator-executed button commands are transmitted back to the system control circuit via the RS485 interface, enabling related operations on the device. [align=center] Figure 2 Device Hardware Block Diagram[/align] 4.1 Signal Detection: This device is mainly used to detect the operating status of the locomotive's main circuit, excitation circuit, and control circuit. Therefore, it is necessary to collect the operating status of these circuits and send this status information to the device's central control board for analysis and judgment. In the design of the detection circuit, a total of 36 detection sampling points are arranged. These test points basically cover the key electrical components of the locomotive and common fault locations. They are connected to the detection points of each control circuit of the locomotive via detection lines, of which 7 detection lines also serve as processing lines. Since the locomotive's control circuits mostly operate under high voltage and high current conditions, and the locomotive's working environment is harsh with severe electromagnetic interference, opto-isolation measures are adopted in the circuit to prevent the locomotive's own electrical noise from interfering with the normal operation of this device. From signal sampling to power supply, complete isolation is achieved, ensuring that this device is unaffected by the locomotive's electrical interference. 4.2 System Control: The CPU uses an Atmel AT89C55WD microcontroller, which is the core control of the entire device. The CPU collects status information from various detection points on the locomotive and, based on the logical relationship of the locomotive's electrical system, determines the working status of each circuit. When a fault occurs in a part of the locomotive, it can issue corresponding control actions through the automatic fault handling board circuit for emergency handling. Simultaneously, it records relevant information such as the fault location and the time of the fault in the EEPROM and sends the recorded data through the RS485 interface to notify the display control circuit to display it on the LCD screen. Commands input by the operator on the display control board are also received by the system controller CPU through the RS485 interface, and the specific operation is completed according to the command content. In addition, to prevent the microcontroller from being accidentally interfered with, causing the program to crash and freeze, the watchdog timer function built into the 89C55WD CPU is utilized. During normal program execution, the watchdog timer is continuously cleared. If the program crashes, the watchdog timer automatically resets the microcontroller, restoring it to normal operation. 4.3 Real-time clock circuit and non-volatile memory circuit: To record the location and time of faults during locomotive traction operations for maintenance reference when the locomotive is in the depot, the device should be equipped with a clock and non-volatile memory circuit. The real-time clock circuit of this device uses the Philips PCF8563 integrated chip. This circuit uses a 32768Hz crystal oscillator, and after calibration, the accuracy can be guaranteed to be within ±10 seconds per month, which basically meets the clock requirements of the monitoring recorder. To record and store fault information, a non-volatile memory chip, 24C32, is used in the circuit. This chip has a storage capacity of 4KB and can record 512 fault locations and the time of occurrence. Both the PCF8563 and 24C32 use the IIC bus. Since the AT89C55WD microcontroller lacks an IIC interface, the microcontroller's input/output ports are used to simulate the IIC interface via software. 4.4 Display and Control: The display controller's CPU also uses an Atmel AT89C55WD microcontroller for control and management. Its main functions are threefold: controlling the large-screen LCD display; completing keyboard scanning; and communicating with the main CPU on the central control board. The device's LCD screen uses a 320×240 dot matrix screen, capable of displaying 15 lines of Chinese characters, with 20 characters per line, meeting the device's display requirements. The LCD driver controller uses a Toshiba T6963C, which supports a wide range of LCD formats and can display characters and graphics on the same screen, as well as providing character attribute functions. Its performance is superior. The T6963C can directly interface with a microcontroller, making control convenient. In this device, we used an 89C55WD microcontroller for control. Following commands from the system control CPU, it displays the required text and graphics on the screen. 4.5 Keyboard: This device has six function keys below the display panel, allowing operators to switch detection circuits, adjust the clock and date, and browse and query recorded data. Key management is handled by the CPU on the display controller. When a key is detected, its key code is transmitted to the system control CPU via the RS485 interface. The CPU analyzes and determines the key's behavior, issuing corresponding control actions or transmitting control commands back via the RS485 interface, and displaying relevant information on the screen according to the key press commands. 5. Software Design The device's software consists of two parts: system control circuit software and display control circuit software. Both programs are written using Keil C51 from Keil Corporation. Keil C51 is currently the latest programming language for 51-core microcontrollers. Its rich library functions and complex computational capabilities can overcome many shortcomings of assembly language in microcontroller programming. Furthermore, the final generated target code, after optimization, is nearly identical to programs written in assembly language. Using Keil C51 frees programmers from the tedious work of assembly language programming, allowing them to focus on writing more optimized and standardized programs. 5.1 System Control Main Program: The program flow is shown in Figure 3. In the main program, initialization is completed first. Then, it waits for the key codes obtained after keyboard scanning. The key codes control the output switching circuit, connecting the signal detection line to the detection loop. The operating status of the corresponding loop is then read, and after logical judgment, the result is sent to the display control, which displays the corresponding text and graphics on the screen. On the other hand, the main program also continuously reads the PCF8563 clock. In case of a fault, it stores the fault code, the current date and time, and other information. The main program also determines whether it is in an online data query state. If it is, it reads the data from the memory and sends it to the serial port register according to the received instruction. The relevant information is then sent to the display controller via the RS485 interface, and the stored content is displayed on the screen. The serial port interrupt program of the system control mainly judges each command message received from the RS485 port, determines the next action based on the message content, and continuously sends the current time information to the display controller to display real-time clock information on the screen. 5.2 Display Control Main Program: The flowchart of the display control main program is shown in Figure 4. It mainly completes keyboard scanning, determines the pressed key, and sends its key code to the system control CPU through the serial interrupt subroutine. The system control circuit then makes corresponding control based on the key press and returns the corresponding information. In the detection state, when the system control CPU performs a certain part detection, it sends the detection status to the display control CPU through code. The CPU then retrieves the corresponding display graphics from the pre-set graphics library based on this code and displays them on the screen. 6. Conclusion The locomotive electrical fault detection and display device introduced in this paper fully utilizes the hardware resources of the 89C55WD microcontroller, featuring a simple peripheral hardware circuit structure and high system reliability. Furthermore, leveraging the powerful capabilities of the C51 programming language, particularly its strong logic operation and control functions, it significantly improves the processing effect of electrical fault detection and judgment, enabling online measurement. This undoubtedly provides a strong guarantee for safe operation and locomotive maintenance. The author's innovation lies in the fact that currently, after a locomotive electrical fault occurs, drivers and crew members rely solely on manual searching with test lights due to the lack of any instruments or meters for detection. Moreover, the judgment of the fault location often depends on the experience of maintenance personnel, which has significant shortcomings. This device utilizes microcontroller detection technology and software processing capabilities to automatically detect and display the location of locomotive electrical faults, solving the drawbacks of manual locomotive inspection and effectively reducing the occurrence of locomotive breakdowns and failures, thus ensuring operational safety. References 1. Wang Yifeng. Statistical Analysis of Emergency Faults of Dongfeng 4 Locomotive [R]. Dalian: Dalian Diesel Locomotive Research Institute, Ministry of Railways, 1997, (4) 2. Sun Yanhua et al. Application of Expert System and Simulation Technology in Locomotive Electrical Testing. Control Engineering. 2003. (3) 3. Zhu Zhiying, Zhao Guanwu. Overhaul of Diesel Locomotives [M]. Beijing: China Railway Publishing House, 1996. 4. Tian Hongping et al. Research on Fault Diagnosis System of Locomotive Electrical Circuit. Journal of Northern Jiaotong University. 2000. (4) 5. Zhang Xueyi. Intelligent Fault Diagnosis System of JK99429A Railway Locomotive. Microcomputer Information. 2001. (1)