# Real-Time Control System for Model Railway Based on SIMIS W Interlocking System
## 1 Introduction  
Modern railway operations rely on advanced signalling systems to ensure safety, efficiency, and reliability. Among these, Siemens' SIMIS W (Sicheres Mikrocomputersystem von Siemens fur den Weltmarkt) electronic interlocking system, a product of Siemens Mobility, is widely adopted for its robust performance and compatibility with dispatcher workstations such as ILTIS-N (Intergiertes Leit und Informationssystem von Siemens). Educational tools replicating such systems play a critical role in preparing students for real-world applications. However, traditional model railway setups often fail to capture the complexity and real-time responsiveness of these advanced systems. This creates a need for practical solutions that bridge this gap in educational environments. To address this gap, we developed a model railway signalling system based on the SIMIS W interlocking system, designed to emulate professional-grade performance and enhance the practical learning experience for students. Digital Command Control (DCC) based systems are commonly used in model railways. DCC systems utilize the open communication protocol XpressNet to manage train operations and control track equipment, such as switches and signals. There are various ways to control DCC model railways, from plug-and-play control modules via DIY solutions [1] to cloud-based solutions. This study aims to develop a simplified model of a real-world interlockingsystem to manage a model railway. The interlocking system is responsible for establishing a train route (a section that a train goes through from one location to another location within a station) for each train entering or departing from the station [2]. The railway model incorporates block and level-crossing systems, necessitating the seamless integration of the new SIMIS W interlocking system with the existing infrastructure. To achieve this, we employed a SIMATIC Programmable Logic Controller (PLC), a widely recognized hardware platform for automation and traffic control [3,4]. The PLC's Profinet connection [5] was leveraged to establish reliable real-time communication, enabling the precise and deterministic exchange of data crucial for synchronizing operations. Real-time communication ensures that information is transmitted, processed, and acted upon within stringent time constraints, a requirement essential for safety-critical applications such as railway signalling. The methodology prioritized compatibility with existing hardware to reduce redundancy and maintain system coherence. The Lenz DCC command station managed train movements. Other trackside components (signals, switches, and level crossings) were controlled using the SIMATIC PLC, supplemented by desktop applications for higher-level processing and human-machine interface functionality. Similar research has been conducted by authors who used an ABB Asea Brown Boveri (a Swedish-Swiss multinational group of companies based in Zurich) PLC to control a model railway entirely [6]. Another study [7] explored using a real-time operating system based on OpenDCC software with an ATmega processor. Their experiments demonstrated that a responsive system can be maintained under high-load conditions even with a low-performance processor. The main difference between this article and [6,7] is in the control system. The approach presented in this paper utilizes a simulation model derived from real interlocking systems widely used in real-life railway control. Other studies focused on creating a control system with its program structure designed in a way which simulates the control of traffic processes only by its external behaviour. In simulation technology, an innovative approach was adopted by modifying and implementing a model of the railway signalling system for integration within a combined system utilizing both a PLC and a personal computer (PC). One of the advantages of the combined approach is the complexity of the control system and its possibilities for use.