<![CDATA[The reliability of the Passenger Information Display System (PIDS) is essential for ensuring safety, passenger comfort, and service quality in railway transportation. In Passenger Coach 612, the running text display delivers real-time travel information, operational status, and safety messages. However, unstable power supply conditions, particularly under-voltage and over-voltage, frequently cause display malfunctions, operational interruptions, and hardware damage. This study proposes an Internet of Things (IoT)-based protection and monitoring system to detect voltage abnormalities and prevent equipment failure. The system employs an ESP32 microcontroller as the main controller, an INA219 sensor for voltage and current measurement, and a relay module for automatic protection. Protection thresholds were set at 4.3 V for under-voltage and 5.7 V for over-voltage based on the EN 50155 standard and field observations. Operational data are transmitted in real time to an IoT platform and a Realtime Database, enabling remote web-based monitoring. Experimental results show that the proposed system accurately detects voltage disturbances, automatically disconnects the power supply under abnormal conditions, and provides reliable real-time monitoring. Sensor calibration yielded a correction factor of K = 0.981, with a voltage measurement error of only 0.02 V compared with a reference digital multimeter. The proposed system improves the reliability of the running text display, enhances maintenance efficiency through continuous remote monitoring, and contributes to safer and more reliable railway passenger information services.]]>
