1-Channel 12V Relay Module with Optocoupler Isolation

This relay module gives a microcontroller a safe, isolated way to switch a mains-voltage or higher-current DC load that the microcontroller's own GPIO pins could never drive directly, bridging the gap between low-voltage logic signals and real-world loads like lights, pumps, fans, or small appliances. A BC547 transistor drives the relay coil from the 12V trigger signal, while an optocoupler sits between the control-side logic and the relay driving circuitry, electrically isolating the microcontroller from any voltage spikes or noise generated on the switched load side.

Switching capacity is rated at 250VAC/10A or 30VDC/10A, covering a genuinely wide range of household AC loads and higher-current DC loads like small motors or solenoid valves from the same board. Three screw-terminal relay contacts are provided - common (C), normally closed (NC), and normally open (NO) - giving flexibility in whether the connected load should be off or on by default when the relay isn't energized.

A freewheeling diode across the relay coil protects the driving transistor from the voltage spike generated when the coil de-energizes, and onboard LED indicators give an at-a-glance visual confirmation of relay state without needing to measure anything with a meter. Mounting holes on the compact 53 x 18 x 18.5mm board make it easy to screw down securely inside an enclosure rather than leaving it loose on wires.

Makers and hobbyists adding mains-voltage or higher-current switching to an Arduino, ESP32, or similar microcontroller project - home automation switches, irrigation pump control, appliance timers - will find this opto-isolated relay module a safe, well-proven way to bridge logic-level control into the real-world electrical loads a project needs to actually act on.