User’s Guide: 12V 4-Channel Relay Module with Optocoupler

Overview

This module allows microcontrollers to control high-voltage devices (AC or DC) using opto-isolated relays. Each channel can be triggered by either HIGH or LOW logic, selectable via jumpers.

Specifications

• Operating Voltage: 12V DC
• Relay Ratings: AC 250V / 10A, DC 30V / 10A
• Trigger Modes: Selectable HIGH or LOW via jumper
• Isolation: Optocoupler per channel
• Control Logic: TTL compatible (3.3V or 5V)
• Current Draw: ~15–20mA per channel

Pinout & Connections

Jumper Settings: Each channel has a jumper to select HIGH or LOW trigger. Set to L for LOW trigger (default), or H for HIGH trigger

Wiring Example (Arduino)

#define RELAY1 6
#define RELAY2 7
#define RELAY3 8
#define RELAY4 9

void setup() {
  pinMode(RELAY1, OUTPUT);
  pinMode(RELAY2, OUTPUT);
  pinMode(RELAY3, OUTPUT);
  pinMode(RELAY4, OUTPUT);
}

void loop() {
  digitalWrite(RELAY1, LOW); // Activate Relay 1
  delay(1000);
  digitalWrite(RELAY1, HIGH); // Deactivate Relay 1
  delay(1000);
}

Use external 12V power for the relay module. Do not power it directly from the microcontroller.

Tips for Reliable Operation

• Use flyback diodes across inductive loads (motors, solenoids).
• Keep signal and power grounds tied together if using separate supplies.
• For ESP32 or STM32 (3.3V logic), ensure optocoupler input thresholds are met—use level shifters if needed.
• Mount inside a ventilated enclosure if switching high current loads.

Troubleshooting

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