How It Works
A relay is a simple electromagnetic switch.
- You send a 5V logic signal (HIGH or LOW, depending on the module) to the IN pin from your microcontroller.
- This signal activates a transistor, which energises an electromagnet (the coil) inside the relay.
- The magnetic field pulls a mechanical switch, instantly connecting or disconnecting the high-power circuit connected to the screw terminals.
- Most modules include an optocoupler, which uses light to send the signal, creating a physical gap that electrically isolates your control circuit (microcontroller) from the load circuit (appliance).
Key Features
- 5V Logic Control: Easily triggered by the digital output pins of most common microcontrollers.
- High-Current Load: Capable of switching loads up to 10A at 250VAC or 10A at 30VDC.
- Optically Isolated: An onboard optocoupler (like the PC817 or EL817) protects your microcontroller from the high-voltage side.
- Status Indicator LEDs: Includes two onboard LEDs:
- Power LED (Red): Lights up when the module is powered (VCC/GND).
- Relay Status LED (Green/Blue): Lights up when the relay is active (triggered).
- Secure Screw Terminals: Provides robust and easy-to-use connections for your high-power load wires.
- Freewheeling Diode: Protects your circuit from voltage spikes (back-EMF) generated when the relay coil is de-energised.
Understanding the Pinout
Low-Voltage Control Side (3 Pins):
- VCC: Connects to the 5V power supply from your microcontroller.
- GND: Connects to the Ground (GND) of your microcontroller.
- IN: The control signal pin. Connects to a digital output pin on your microcontroller.
High-Voltage Load Side (3 Screw Terminals):
- COM (Common): The central pin. This is typically where you connect the “live” wire from your appliance or power source.
- NC (Normally Closed): This contact is connected to COM by default (when the relay is off). The circuit is complete.
- NO (Normally Open): This contact is disconnected from COM by default (when the relay is off). The circuit is broken.
How to use NO/NC:
- To turn a device ON when you trigger the relay (e.g., a light), connect your circuit using COM and NO.
- To turn a device OFF when you trigger the relay, connect your circuit using COM and NC.
Common Applications
- Home Automation: Control AC lights, fans, and coffee makers.
- IoT Projects: Build smart plugs or web-controlled switches.
- Robotics: Control high-power motors and actuators.
- DIY Projects: Safely switch any high-voltage or high-current device.
Technical Specifications
- Control Voltage (VCC): 5V DC
- Trigger Current: 15-20mA
- Max Load Rating: 10A 250VAC / 10A 30VDC
- Switching Time: ~10ms
- Module Dimensions: (Typical dimensions, e.g., 43mm x 17mm x 19mm)
What’s Included
- 1 x 5V Single-Channel Relay Module













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