Relay is a device controlling large current through small current. A relay system usually consists of small current circuit, large current circuit, and circuit conversion part. When the low current circuit reaches a certain condition, it will trigger the high current circuit through the conversion section. This method is more safe and flexible than direct control of large current circuits.
Common ways of circuit conversion are electromagnetic, solid state, magnetic spring, temperature, light, etc. Relay Card is a reed type. With the help of Relay Card and other sensors, it is easy to automatically turn on air conditioner when detected the temperature is high.
Relay Card allows you to control the circuit of high voltage with a low voltage, say 5V from the Carduino. The relay on the Relay Card is normally-opened. You can connect any high voltage appliance through the 2-pin terminal block connector on the front of the board. The maximum voltage ratings for the high voltage appliances are 3A@250V AC and 3A@30V DC. When you apply a 5V signal to the Relay Card, the relay gets close, and the connected device will turn ON.
Longan Cards is a unique open source development platform designed by Longan Labs. As a plug and play development platform, Longan Cards allows you to quicky build wide array of prototypes and applications in no time. A full set of Arduino libraries and plenty of example codes are available to play with Longan Cards platform.
CAUTION: Don't touch Relay Card while connected to the mains electricity or high voltage DC.