User’s Guide: 12V 1-Channel Relay Module (High/Low Trigger, Optocoupler)
Overview
This module allows microcontrollers to safely control high-voltage devices using a relay with optocoupler isolation. It supports both HIGH and LOW level triggering, selectable via jumper, making it flexible for different logic levels.
Specifications
| Parameter | Value |
|---|---|
| Operating Voltage | 12V DC |
| Trigger Voltage | 3.3V or 5V logic compatible |
| Relay Rating | AC 250V / 10A, DC 30V / 10A |
| Trigger Mode | Selectable HIGH or LOW via jumper |
| Isolation | Optocoupler per channel |
| Indicators | Power (green LED), Relay status (red LED) |
| Module Size | ~50mm × 26mm × 18.5mm |
Pinout & Terminals
Input Side
| Pin | Description |
|---|---|
| VCC | 12V power supply (+) |
| GND | Ground (-) |
| IN | Signal input from microcontroller |
Output Side (Relay Terminals)
| Terminal | Function |
|---|---|
| COM | Common contact |
| NO | Normally Open (connected when relay is ON) |
| NC | Normally Closed (connected when relay is OFF) |
Trigger Jumper: Set to L for LOW-level trigger (default), or H for HIGH-level trigger.
Wiring Example (Arduino)
#define RELAY_PIN 7
void setup() {
pinMode(RELAY_PIN, OUTPUT);
}
void loop() {
digitalWrite(RELAY_PIN, LOW); // Activate relay if jumper is set to LOW trigger
delay(1000);
digitalWrite(RELAY_PIN, HIGH); // Deactivate relay
delay(1000);
}
Use a separate 12V power supply for the relay module. Do not power it directly from the microcontroller
Integration Tips
- For ESP32 or STM32 (3.3V logic): Ensure optocoupler input threshold is met. Use a transistor or level shifter if needed.
- Use flyback diodes across inductive loads to prevent voltage spikes.
- Keep grounds common between microcontroller and relay module if using separate supplies.
- Mount inside a ventilated enclosure if switching high current loads.
Troubleshooting
| Issue | Cause | Solution |
|---|---|---|
| Relay LED on, no click | Wrong trigger level or insufficient current | Check jumper and power supply |
| No relay response | IN pin not receiving correct signal | Verify GPIO logic and jumper setting |
| Arduino resets | Relay draws too much current | Use separate power supply for relay |