This study aims to model and simulate the control system of a coin-operated self-service washing machine using a formal Deterministic Finite Automata approach. Along with the rapid growth of the laundry industry in urban areas, the reliability of the machine's control logic is a crucial aspect to ensure consistent, safe, and unambiguous operations. DFA is chosen as the modeling foundation because its deterministic nature guarantees that every pair of state and input has exactly one subsequent state, making it highly ideal for hardware control systems. The DFA model in this study is mathematically defined as a five-tuple consisting of nine states, ranging from the ready condition to completion, ten input symbols encompassing user actions and internal timer signals, and fifteen clearly defined transition rules. The system supports three washing program variations: a quick program, a normal program, and an intensive program, which are uniquely converged into a single sequential phase flow comprising washing, rinsing, and spinning. To verify the model, this study implements an interactive web-based simulation using pure web programming technologies, equipped with state transition diagram visualization and real-time event logging. Scenario-based testing was conducted through eight comprehensive test cases, covering normal flows, cancellation mechanisms with coin refunds, and rejection of invalid inputs. The test results validate that all transitions operate according to specifications, the reset mechanism functions optimally, and the final state can only be reached after the washing cycle is fully completed. In conclusion, this model proves to be an effective, structured, and verifiable formal framework, which is not only relevant as a learning medium for automata theory but also as a solid logical foundation for the future development of microcontroller-based or Internet of Things automatic machine control systems.