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Relay Module

An electrically-controlled switch — let a 5V pin switch a much bigger load.

Buy Relay module · Amazon

How it works

A relay is a switch operated by an electromagnet, so a tiny control signal can switch a far larger load (a lamp, a motor, mains appliances). A relay module adds the driver transistor, a flyback diode, and screw terminals so you can drive it straight from a microcontroller pin.

The control side has VCC, GND, and IN. The load side has three screw terminals: COM (common), NO (normally-open, closed when active) and NC (normally-closed). Many modules are active-LOW — IN LOW energizes the relay.

Pins

VCC
To 5V.
GND
To GND.
IN
To a digital pin (often active-LOW).
COM / NO / NC
Load side — your switched circuit.

Ratings

Coil
5 V (module)
Contacts
e.g. 10 A @ 250 VAC / 30 VDC
Trigger
Often active-LOW

Tips

  • ⚠️ Mains voltage is dangerous — if you're new, practice with a low-voltage load first.
  • Use COM + NO for 'on when activated'.
  • If it switches backwards, your module is active-LOW — invert the code.