KY-019 Relay Module is used to control AC circuits, the relay acts as a switch that responds to a signal received from the Arduino, it has an integrated LED that indicates if the signal is high or low.The KY-019 consist of a 1MΩ resistor, a LED, a 1N4007 rectifier diode and a 5VDC relay capable of handling up to 250VAC and 10A.