Wiring Arduino to 5V Relay Module 4-Channel: High and Low Trigger Explained

A 5V Relay Module lets Arduino control high-power electrical devices like 220V household lights or motors. This 4-channel board supports up to 250V/10A per channel, with optocoupler isolation to protect Arduino from voltage surges.

Required Components

• Arduino UNO R3
• 4-Channel 5V Relay Module (High & Low Trigger)
• 9V 2A Power Adapter for Arduino
• LED Bulb E27 7W with E27 socket
• AC Power cord 2*0.75, 1.5-3m
• Breadboard MB-102 (optional for additional circuits)
• Male-to-male and male-to-female jumper wires 20cm

Wiring Diagram

Connect wires from Arduino to the Relay Module as follows:

Arduino	Relay Module
5V	DC+
GND	DC-
Pin 2	IN1
Pin 3	IN2
Pin 4	IN3
Pin 5	IN4

For the 220V AC power circuit, wire the light through Relay Channel 1:

• Live wire (brown) from AC source → COM1
• Neutral wire (blue) → light bulb
• Wire from light bulb → NO1

Important: Keep the 220V AC wiring completely separate from Arduino signal wires at all connection points. Accidental contact can destroy your Arduino board.

Understanding COM, NO, NC Pins

Each relay channel has 3 terminals for connecting the load:

• COM (Common) — the middle terminal, connects to the power source
• NO (Normal Open) — connects only when the relay activates, ideal for loads you want to turn on
• NC (Normal Closed) — stays connected when the relay is inactive, disconnects when the relay activates

Relay Trigger Modes

The 4-channel relay board has yellow jumpers that let you choose between 3 trigger modes:

Active HIGH Mode (H)

Set all jumpers to the H side. The relay activates when Arduino sends a HIGH signal to the IN pin. When HIGH is received, the relay switches from NC to NO, turning the light on. After 10 seconds, Arduino sends LOW and the relay switches back to NC, turning the light off for 2 seconds.

Hybrid Mode (H+L)

Set jumpers on both H and L sides. Relays can switch in response to both HIGH and LOW signals, allowing you to control multiple devices simultaneously based on different logic inputs.

Active LOW Mode (L)

Set all jumpers to the L side. The relay activates when Arduino sends a LOW signal to the IN pin. When LOW is received, the relay switches from NC to NO, turning the light on for 2 seconds. Then Arduino sends HIGH and the relay switches back to NC, keeping the light off for 10 seconds.

Arduino Code for Relay Control

The source article did not include code, so here is a working example you can copy and paste. This code demonstrates all three trigger modes — pick the section that matches your jumper configuration.

// Define relay control pins connected to Arduino
const int relay1 = 2;
const int relay2 = 3;
const int relay3 = 4;
const int relay4 = 5;

void setup() {
  // Set all relay pins as outputs
  pinMode(relay1, OUTPUT);
  pinMode(relay2, OUTPUT);
  pinMode(relay3, OUTPUT);
  pinMode(relay4, OUTPUT);

  // Start with all relays off (depends on jumper mode)
  digitalWrite(relay1, LOW);
  digitalWrite(relay2, LOW);
  digitalWrite(relay3, LOW);
  digitalWrite(relay4, LOW);

  Serial.begin(9600);
}

void loop() {
  // ===== Active HIGH Mode =====
  // Light ON for 10s, OFF for 2s
  Serial.println("Active HIGH: Relay ON 10s");
  digitalWrite(relay1, HIGH); // Trigger relay
  delay(10000);              // Wait 10 seconds

  Serial.println("Active HIGH: Relay OFF 2s");
  digitalWrite(relay1, LOW);  // Deactivate relay
  delay(2000);               // Wait 2 seconds

  // ===== Hybrid Mode =====
  // Control Relay1 (HIGH) and Relay2 (LOW trigger) simultaneously
  Serial.println("Hybrid: Relay1 ON, Relay2 OFF");
  digitalWrite(relay1, HIGH);
  digitalWrite(relay2, HIGH); // If L-side jumper is set, this LOW signal triggers that relay
  delay(5000);

  Serial.println("Hybrid: Relay1 OFF, Relay2 ON");
  digitalWrite(relay1, LOW);
  digitalWrite(relay2, LOW);  // If L-side jumper is set, this LOW signal triggers that relay
  delay(5000);

  // ===== Active LOW Mode =====
  // Light ON for 2s, OFF for 10s (logic inverted)
  Serial.println("Active LOW: Relay ON 2s");
  digitalWrite(relay1, LOW);  // LOW trigger activates the relay
  delay(2000);

  Serial.println("Active LOW: Relay OFF 10s");
  digitalWrite(relay1, HIGH); // HIGH trigger deactivates the relay
  delay(10000);
}

Points to adjust based on your mode:

• If using only Active HIGH, remove the Hybrid and Active LOW sections and keep just the first block
• If using Active LOW, invert the logic — use digitalWrite(relay1, LOW) to activate instead of HIGH
• Arduino pin numbers (2-5) can be changed to match your wiring

How to Upload Code to the Board

1. Open Arduino IDE and paste the code above
2. Go to Tools → Port and select the port your board is connected to
3. Go to Tools → Board and select Arduino UNO
4. Click the Upload button (right arrow icon) and wait for “Done uploading”

[image: Screenshot of Arduino IDE showing the Tools menu with Port and Board selections highlighted, plus the UNO board and COM3 port labeled]

Reference Video

• YouTube: Arduino Relay Module 4 Channel Tutorial

Summary

The 5V 4-channel Relay Module extends Arduino’s capability to control 220V AC appliances safely, thanks to built-in optocoupler isolation. Choosing between High and Low trigger modes depends on the logic signals your Arduino outputs, and the jumper configuration on the board determines which signals the relays respond to. Understanding this makes it straightforward to adapt the setup for home automation projects.