The Relay Expansion Board category features a range of relay-based control modules designed for automation and industrial applications. These boards provide reliable switching for high-voltage or high-current circuits, enabling seamless integration with microcontrollers, PLCs, and other control systems. Key products include solid-state relay modules, electromechanical relay boards, and optocoupler-isolated relay expansions. Common features include multi-channel configurations (4-channel, 8-channel, etc.), wide voltage compatibility (5V-240V), and robust protection against electrical noise. These boards are essential for applications like motor control, HVAC systems, and automated test equipment, offering precise signal routing and electrical isolation.