4-Channel 5V Relay Module (HW-304, SRD-05VDC-SL-C)

The 4-Channel 5V Relay Module HW-304 is a practical interface board for controlling multiple electrical loads from a low-voltage controller. Built around four SRD-05VDC-SL-C electromechanical relays, it allows a 5V logic control signal to operate isolated relay contacts, so an Arduino, Raspberry Pi GPIO interface circuit, PLC output, sensor board or other digital controller can switch lamps, pumps, fans, solenoids, motors and other equipment independently. Each relay is an SPDT changeover switch with three screw-terminal connections: COM, NO and NC. Use COM and NO when the load should normally remain OFF and turn ON only when the relay is activated. Use COM and NC when the load should normally remain ON and turn OFF when triggered. The module requires a 5V supply for relay operation, and each channel typically needs around 15–20mA drive current for switching, making it suitable for common maker and embedded-control projects with proper driver capability. This module is popular in India for Arduino relay projects, Raspberry Pi home automation, IoT appliance switching and workshop test setups because it combines four relay outputs on one compact PCB. The relay contacts support up to 10A switching capacity in spite of the small relay size, with ratings of 250V AC maximum or 30V DC maximum as per the SRD relay specification. The board provides individual input pins IN1 to IN4 plus VCC and GND, while each output channel has NC, COM and NO terminals for wiring the load circuit. Use the HW-304 when you need four separate relay-controlled outputs from one microcontroller board. Typical projects include room light automation, fan and pump switching, door-lock control, irrigation systems, lab automation, alarm panels and multi-channel equipment control. Package includes one 4-channel 5V relay module fitted with four SRD-05VDC-SL-C relays. Always follow safe wiring practices and use qualified help when switching mains voltage.