Key benefits Enables direct control of a circuit from a USB serial port, helping automate testing, prototyping, and remote operation without manual switching. Builtin overcurrent protection to guard the relay and connected equipment. The relay output terminals function as an electronic switch, and the module does not supply load voltage at the load end. Simple, predictable switching behavior: when the coil is deenergized, COM is connected to NC; when the coil is energized, COM is connected to NO. Upgraded and advanced version with a optocoupler protection circuit to prevent interference and to support speed USB serial transmission. What it is and how it works USB serial port control relay: a relay module designed to be driven from a USB serial interface, suitable for automation, testing, and development workflows. The relay contacts act as a dry switch for the load circuit. The module provides no load voltage; you supply the load power through COM and connect to NC or NO as required. When the control signal energizes the relay coil, COM connects to NO; when the coil is off, COM connects to NC. This behavior provides a clear default state and a reliable changeover for switching logic or power paths. The upgraded design includes an optocoupler protection circuit that helps isolate the control side from the load side, reducing interference and enabling more reliable speed operation. Key features and attributes Interface: USB serial port control relay for convenient integration with computers, microcontrollers, and automated test rigs. Protection: overcurrent protection helps safeguard the relay and the connected circuit. Isolation: optocoupler protection circuit provides electrical isolation between control and load, improving noise immunity and reliability. Switching behavior: COMNC when deenergized; COMNO when energized, suitable for normally closed or normally open switching schemes. Output nature: the relay output is a switch, not a source of power for the load end; use an external supply for the load as required. Compatibility and integration Designed to work with standard USB serial control workflows, enabling straightforward integration into development boards, PC software, and automated test setups. Suitable for applications that require switching of external circuits via a reliable, isolated relay interface controlled from software. Practical applications and use scenarios Laboratory automation and testing: run devices under test from a PC or microcontroller, sequencing relay operations to control power to peripherals, sensors, or DUTs (devices under test). Prototyping and development: quickly add controllable switching to projects that require turning on/off heaters, fans, indicators, or other loads driven by an external supply. PCcontrolled equipment and automation: enable remote or scheduled control of equipment in a lab, classroom, or workshop, while maintaining isolation between control hardware and power circuits. Setup and usage hints Connect the load circuit through COM and either NC or NO according to your desired default state. Power the module via USB and issue serial commands to energize or deenergize the relay coil. Ensure the load supply is provided separately from the module, respecting the relay's ratings and the load's voltage and current requirements. Take advantage of the optocoupler isolation to minimize interference from the load side into the USB control side. Safety and general guidelines The module provides a dry contact switch; do not rely on it to source load voltage. Use your own supply for the load as appropriate. Observe the relay's electrical ratings and ensure the load current and voltage remain within the safe operating area. Use proper wiring practices to maintain isolation benefits from the optocoupler protection circuit and to reduce noise coupling. This description preserves the core function, behavior, and upgraded features of the USB serial port control relay while presenting clear, customerfriendly guidance. It highlights how the product solves control, isolation, and interference concerns in practical applications, without adding extraneous details.