Relay
Controlling Relay 1CH with Arduino Uno
What is the Relay 1CH?
Relay 1CH practical reference
A single-channel relay module with opto-isolation, letting a microcontroller safely switch AC appliances or high-current DC loads.
Key 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
Pinout and connection notes
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.
- VCC: Power, 5V DC, control side
- GND: Ground, control side
- IN: Signal input from the MCU — active LOW on most modules
- COM: Common, switching side
- NO: Normally open — connects to COM when energized
- NC: Normally closed — connects to COM when de-energized
Integration checklist
- Confirm the exact part number and breakout-board revision.
- Verify supply voltage, current demand, logic levels, and signal direction against the datasheet.
- Check controller pin assignments and bus address or interface mode against the example code.
- Power up with external loads disconnected, then test signals before full integration.
- If readings or communication fail, check power and ground first, then pin mapping, interface settings, and library initialization.
Troubleshooting and reproducibility
Record the board used, wiring, library/version, supply arrangement, and measured behavior. Use the selected board-specific wiring example as the source of truth. Never assume visually similar modules share identical voltage tolerance or pin order.
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 |
Swipe sideways to see every column →
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.
Related Components
Active Buzzer
Self-oscillating buzzer that beeps with just a single HIGH signal — no PWM required.
BLDC ESC
High-speed brushless motor and electronic speed controller combo.
Continuous Servo
Modified servo that spins continuously like a geared motor.
Relay 4CH
4-channel relay board for controlling multiple appliances — ideal for home automation projects.
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