4 Channel Relay Module with light coupling 5V

Usage Guide

How It Works

The module uses an independent optocoupler for each channel to isolate the low-voltage control side from the high-voltage load side. When the trigger input (IN1, IN2, IN3, or IN4) receives the appropriate signal (HIGH or LOW depending on jumper configuration), the optocoupler activates, which energizes the corresponding relay coil . The energized relay switches the common (COM) terminal connection from the normally closed (NC) contact to the normally open (NO) contact, completing the circuit to your load .

The VCC-JD-VCC jumper (typically located near the power input header) connects the logic power supply to the relay coil power supply. When driving multiple relays simultaneously, you can remove this jumper and supply separate power to the JD-VCC pin to avoid overloading your microcontroller’s 5V regulator .

Important Operating Principle: For most 4-channel optocoupler relay modules, the relay activates when the input signal is LOW (0V) by default . This is because the optocoupler LED is typically wired with its anode to VCC and cathode to the IN pin. When the IN pin is pulled LOW, current flows through the LED, activating the optocoupler and relay .

Wiring Instructions

Step 1 – Control Side Connection (to Microcontroller)

Connect the 4-pin male header (2.54mm pitch) as follows:

*Note: Pin numbering may vary – some modules have a separate 4-pin header for IN1-IN4 and a 2-pin header for VCC/GND.*

Step 2 – Load Side Connection (to High-Power Devices)

Each relay channel has a 3-pin screw terminal block:

Wiring Example 1 – Controlling an AC Light Bulb (NO configuration):

• Connect AC Live wire → COM terminal

• Connect AC Neutral wire → Light bulb neutral

• Connect Light bulb live → NO terminal

• When relay activates, the circuit closes and the light turns ON

Wiring Example 2 – Controlling a DC Motor (NO configuration):

• Connect DC power supply positive → COM terminal

• Connect Motor positive → NO terminal

• Connect Motor negative → DC power supply negative directly

⚠️ Safety Warning: High voltage (110V/220V AC) is dangerous. Ensure all connections are properly insulated. Always disconnect power before wiring. Use appropriately gauged wire for your load current. Mount the module in an enclosure for permanent installations .

Trigger Mode Configuration (High/Low Level Jumper)

The module features jumper-selectable trigger modes for each channel, typically labeled S1, S2, S3, S4 or a single H/L jumper block per channel .

Important: Many 4-channel optocoupler relay modules are designed to be active LOW by default . This means with the jumper in the LOW position, the relay activates when you pull the IN pin to GND (digitalWrite LOW). This is actually the more common configuration for these modules.

Recommended Settings by Microcontroller:

To change trigger mode:

1. Locate the jumper(s) on the PCB (small black plastic caps covering three header pins)

2. Gently remove the jumper cap

3. Reposition it over the desired pins (refer to silkscreen labels: LOW/GND or HIGH/VCC)

4. Each channel may have its own jumper – configure independently

VCC-JD-VCC Jumper (Separate Relay Power Option)

By default, a jumper connects VCC to JD-VCC, powering the relay coils from the same 5V supply as the logic circuit .

Why use separate power:

• The relay coils draw approximately 60mA per channel when active

• With all 4 relays active, total current can reach 240mA, which may exceed your microcontroller’s 5V regulator capacity

• Using separate power prevents overloading and potential damage to your microcontroller

When to remove the jumper:

• Controlling 2 or more relays simultaneously

• Using a low-current 5V supply (e.g., USB from a computer)

• Driving heavy inductive loads that cause voltage fluctuations

• When true optocoupler isolation is required

How to use separate power:

1. Remove the VCC-JD-VDC jumper cap

2. Connect external 5V supply to JD-VCC pin (positive) and GND pin (negative)

3. Connect microcontroller 5V to VCC pin (positive) and the same GND pin

4. The logic and relay circuits are now independently powered

Note: For true optocoupler isolation, do not connect the module GND to Arduino ground after removing the jumper .

Arduino Sample Code (Low-Level Trigger Configuration)

Most 4-channel optocoupler relay modules use active LOW triggering. The following code is based on this common configuration .

// 4 Channel Relay Module - Low Level Trigger (Default configuration)
// Relay activates when pin is set to LOW (0V)

const int RELAY1 = 3;  // IN1 connected to digital pin 3
const int RELAY2 = 4;  // IN2 connected to digital pin 4
const int RELAY3 = 5;  // IN3 connected to digital pin 5
const int RELAY4 = 6;  // IN4 connected to digital pin 6

#define RELAY_ON   0   // LOW = relay ON (active LOW)
#define RELAY_OFF  1   // HIGH = relay OFF

void setup() {
  pinMode(RELAY1, OUTPUT);
  pinMode(RELAY2, OUTPUT);
  pinMode(RELAY3, OUTPUT);
  pinMode(RELAY4, OUTPUT);
  
  // Initialize all relays to OFF state
  digitalWrite(RELAY1, RELAY_OFF);
  digitalWrite(RELAY2, RELAY_OFF);
  digitalWrite(RELAY3, RELAY_OFF);
  digitalWrite(RELAY4, RELAY_OFF);
}

void loop() {
  // Turn ON Relay 1 only
  digitalWrite(RELAY1, RELAY_ON);
  delay(2000);  // Wait 2 seconds
  digitalWrite(RELAY1, RELAY_OFF);
  delay(500);
  
  // Turn ON Relay 2 only
  digitalWrite(RELAY2, RELAY_ON);
  delay(2000);
  digitalWrite(RELAY2, RELAY_OFF);
  delay(500);
  
  // Turn ON Relay 3 only
  digitalWrite(RELAY3, RELAY_ON);
  delay(2000);
  digitalWrite(RELAY3, RELAY_OFF);
  delay(500);
  
  // Turn ON Relay 4 only
  digitalWrite(RELAY4, RELAY_ON);
  delay(2000);
  digitalWrite(RELAY4, RELAY_OFF);
  delay(1000);
  
  // Turn ON all relays simultaneously
  digitalWrite(RELAY1, RELAY_ON);
  digitalWrite(RELAY2, RELAY_ON);
  digitalWrite(RELAY3, RELAY_ON);
  digitalWrite(RELAY4, RELAY_ON);
  delay(3000);
  
  // Turn OFF all relays
  digitalWrite(RELAY1, RELAY_OFF);
  digitalWrite(RELAY2, RELAY_OFF);
  digitalWrite(RELAY3, RELAY_OFF);
  digitalWrite(RELAY4, RELAY_OFF);
  delay(1000);
}

Raspberry Pi (Python) Sample Code

import RPi.GPIO as GPIO
import time

# Set up GPIO
GPIO.setmode(GPIO.BCM)

# Define relay pins (adjust according to your wiring)
RELAY1 = 17
RELAY2 = 18
RELAY3 = 27
RELAY4 = 22

# Define constants
RELAY_ON = GPIO.LOW   # LOW = relay ON (active LOW)
RELAY_OFF = GPIO.HIGH # HIGH = relay OFF

# Setup relay pins as outputs
GPIO.setup(RELAY1, GPIO.OUT)
GPIO.setup(RELAY2, GPIO.OUT)
GPIO.setup(RELAY3, GPIO.OUT)
GPIO.setup(RELAY4, GPIO.OUT)

# Initialize all relays to OFF
GPIO.output(RELAY1, RELAY_OFF)
GPIO.output(RELAY2, RELAY_OFF)
GPIO.output(RELAY3, RELAY_OFF)
GPIO.output(RELAY4, RELAY_OFF)

try:
    while True:
        # Turn ON Relay 1
        GPIO.output(RELAY1, RELAY_ON)
        print("Relay 1 ON")
        time.sleep(2)
        GPIO.output(RELAY1, RELAY_OFF)
        print("Relay 1 OFF")
        time.sleep(1)
        
        # Turn ON Relay 2
        GPIO.output(RELAY2, RELAY_ON)
        print("Relay 2 ON")
        time.sleep(2)
        GPIO.output(RELAY2, RELAY_OFF)
        print("Relay 2 OFF")
        time.sleep(1)
        
        # Turn ON Relay 3
        GPIO.output(RELAY3, RELAY_ON)
        print("Relay 3 ON")
        time.sleep(2)
        GPIO.output(RELAY3, RELAY_OFF)
        print("Relay 3 OFF")
        time.sleep(1)
        
        # Turn ON Relay 4
        GPIO.output(RELAY4, RELAY_ON)
        print("Relay 4 ON")
        time.sleep(2)
        GPIO.output(RELAY4, RELAY_OFF)
        print("Relay 4 OFF")
        time.sleep(1)

except KeyboardInterrupt:
    GPIO.cleanup()
    print("Program terminated")

Preventing Relay Chatter During Microcontroller Boot

When your microcontroller boots up, GPIO pins may default to HIGH or LOW unpredictably. To prevent relay chatter during boot:

void setup() {
  // First enable internal pull-up, then set to output
  pinMode(RELAY1, INPUT_PULLUP);
  pinMode(RELAY1, OUTPUT);
  digitalWrite(RELAY1, RELAY_OFF);
  // Repeat for other channels...
}

This technique ensures the relay stays OFF until your code explicitly activates it .

Installation Tips

• Mounting: Secure the module using the four 3.1mm mounting holes with M3 screws. The board has mounting holes at each corner for easy installation

• Ventilation: Allow adequate airflow around the module, especially when switching high currents continuously

• Wire Gauge: Use 14-22 AWG wire for load connections depending on current. For 10A loads, minimum 18 AWG copper wire is recommended

• Enclosure: For permanent installations, mount the module inside a UL-listed electrical enclosure with appropriate strain relief

• PCB Isolation Slot: The physical isolation slot on the PCB separates the control and load areas. Do not bridge this slot with wires or solder