This is a 5v 4-channel relay interface board, be able to control various appliances, and other equipments with large current. A relay can be used to control high voltages with a low voltage by connecting it to an mcu. The 4 relays on the module are independent of each other, once a relay is triggered by the low level, the corresponding led lights will be lit and accompanied by a crisp sound. It can be controlled directly by microcontroller(arduino, raspberry pi, 8051, avr, pic, dsp, arm, msp430, ttl logic). Electrobot 4 channel relay module gives more protection to your microcontroler as it has optocoupler switch. The product is simplified version of costly imported modules.