Blog

5V 1 Channel Relay Active low

Posted by

Ekostra Electronics

April 13, 2025

On April 13, 2025

5V 1 Channel Relay Module (Active Low Trigger)

Low-level triggered single relay module with optocoupler isolation for Arduino/Raspberry Pi projects

Introduction

The 5V 1 Channel Relay Module is an electrically operated switch that allows you to control high voltage/high current devices (up to 250VAC/10A) with low voltage circuits (5V). This version uses an active low trigger signal, meaning the relay activates when the control pin goes LOW (0V).

Key Features

🔌 Active Low Trigger

Activates when control signal goes LOW (0V)

⚡ High Power Control

10A @ 250VAC or 30VDC

🔒 Optoisolation

️4N25 optocoupler protects control circuit

💡 Status LEDs

Power + Relay activation indicators

Technical Specifications

Trigger Voltage	5V DC (Active LOW signal)
Trigger Current	~15-20mA
Max Switching Current	10A @ 250VAC or 30VDC
Default State	Normally Open (NO)
Contact Type	1 Form A (SPST – Single Pole Single Throw)
Optocoupler	4N25 (or equivalent)
Operating Temperature	-40°C to +70°C
Module Dimensions	50mm x 26mm x 18mm (L×W×H)

Pin Configuration

Pin Label	Description	Connection
VCC	5V Power Input	Connect to 5V supply
GND	Ground	Connect to system ground
IN	Control Signal (Active LOW)	Connect to microcontroller pin
NO	Normally Open Contact	Load connection (open when relay off)
COM	Common Contact	Load power input
NC	Normally Closed Contact	Load connection (closed when relay off)

Note: This module has jumper-selectable high/low level trigger (default is active LOW)

Wiring with Arduino

Arduino Relay Wiring

// Arduino Active LOW Relay Control
const int relayPin = 8;  // Connected to IN pin

void setup() {
  pinMode(relayPin, OUTPUT);
  digitalWrite(relayPin, HIGH); // Start with relay OFF (active LOW)
}

void loop() {
  digitalWrite(relayPin, LOW);  // Activate relay
  delay(2000);
  digitalWrite(relayPin, HIGH); // Deactivate relay
  delay(2000);
}

Trigger Logic Explained

Active LOW Mode

Relay activates when:

Control Pin: LOW (0V)

LED turns ON when activated

Default State

Module starts with:

Relay: OFF

Control pin should be HIGH (5V) initially

Important: For active HIGH mode, move the jumper to the HIGH position (check your module's markings)

Application Examples

🏠 Home Automation

Control lights, fans, or appliances

🌱 Irrigation Systems

Automatic watering control

🔌 Power Switching

Safe control of high voltage devices

🚗 Automotive Projects

Remote starter or accessory control

Safety Precautions

⚠️ High Voltage Warning: Use extreme caution when working with mains voltage
🔧 Use proper insulation for all high voltage connections
📏 Maintain adequate clearance between low and high voltage sections
💡 Always disconnect power before making wiring changes
🔍 Double-check all connections before applying power

Hotline 24/7