สวิตช์อุปกรณ์ไฟบ้านด้วยรีเลย์

Sometimes you want your Arduino to switch a lamp or a fan, not just an LED. For mains-powered gear you reach for a relay. 💡

A relay is an electrically controlled switch. A small coil current pulls a metal contact closed, connecting a totally separate, much higher-power circuit.

The coil and the contacts never touch electrically. This isolation is why a 5V Arduino can safely command a 220V device without sharing wires.

Grab a ready-made relay module. It already has the driving transistor, a flyback diode, and screw terminals, so you just supply a control signal.

A typical module has three pins: VCC, GND, and a signal input. Connect signal to any Arduino digital pin to control the relay.

Treat the relay like an LED. Set the pin HIGH or LOW to close or open the contact, depending on how your module is wired.

Many modules are active-low: LOW turns the load on and HIGH turns it off. Test yours so the logic in your sketch matches reality.

The output side offers NO and NC contacts. Normally Open stays off until triggered; Normally Closed is on until the relay switches.

Run one mains wire to the COM terminal and the other to NO. When the relay clicks, the circuit closes and your device powers up.

Mains voltage can kill. Never touch live terminals, keep the high-voltage side enclosed, and have an adult or pro check anything wired to the wall. ⚠️

When the relay switches you hear a satisfying click as the coil snaps the contact. That sound confirms your code reached the real world.

What is the main reason a relay is used to switch mains-powered devices from an Arduino?

A relay is an isolated switch: a small signal closes contacts that power big loads. Use a module, mind active-low logic, and respect mains safety. 🚀