Relay
Controlling Relay 1CH with Arduino Uno
What is the Relay 1CH?
A single-channel relay module with opto-isolation, letting a microcontroller safely switch AC appliances or high-current DC loads.
Specifications
| Control side | 5 V DC, opto-isolated, ~15-20 mA when energized |
| Switching side | Up to 250V AC / 10A or 30V DC / 10A on the common SRD-05VDC-SL-C relay used on most of these boards |
| Trigger logic | Active LOW on most modules — a LOW signal closes the relay, HIGH releases it. Some boards are active HIGH, check the silkscreen or test with a multimeter first |
| Indicator | Onboard LED lights when the relay is energized |
Relay 1CH Pinout
| Pin | Name | Description |
|---|---|---|
| 1 | VCC | Power, 5V DC, control side |
| 2 | GND | Ground, control side |
| 3 | IN | Signal input from the MCU — active LOW on most modules |
| 4 | COM | Common, switching side |
| 5 | NO | Normally open — connects to COM when energized |
| 6 | NC | Normally closed — connects to COM when de-energized |
If you're switching mains voltage, treat COM/NO/NC as a separate high-voltage circuit — keep it physically isolated from the 5V control side and never touch it while powered.
Setting Up Relay 1CH with Arduino Uno
Library
—
No library required — just a digital output pin
Wiring
| Component pin | Arduino Uno pin | Note |
|---|---|---|
| VCC | 5V | Powers the relay module's onboard optocoupler + coil driver |
| GND | GND | — |
| IN | Pin 7 | Most modules are active-LOW: writing LOW energizes the relay |
Example code
If you are switching mains voltage on the relay's dry contacts, that wiring is a separate, high-risk circuit — keep it isolated from the low-voltage side and, if in doubt, have someone qualified do the mains wiring.
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