4-Channel DC 5V / 12V (Active Low) Relay Module with Optocoupler

  • RM18.00

  • Product Code: 4 Relay Module Board - LOW
  • Availability: In Stock

A relay is an electrically operated device. It has a control system and (also called input circuit or input contactor) and controlled system (also called output circuit or output contactor). It is frequently used in an automatic control circuit. To put it simply, it is an automatic switch to controlling a high-current circuit with a low-current signal.

The advantages of a relay lie in its lower inertia of the moving, stability, long-term reliability and small volume. It is widely adopted in devices of power protection, automation technology, sport, remote control, reconnaissance, and communication, as well as in devices of electromechanics and power electronics. Generally speaking, a relay contains an induction part which can reflect input variable like current, voltage, power, resistance, frequency, temperature, pressure, speed and light etc. It also contains an actuator module (output) which can energize or de-energize the connection of controlled circuit. There is an intermediary part between input part and an output part that is used to coupling and isolate input current, as well as actuate the output. When the rated value of the input (voltage, current and temperature etc.) is above the critical value, the controlled output circuit of the relay will be energized or de-energized.



  • SMD optocoupler isolation
  • Good in safety. In power system and high voltage system, the lower current can control the higher one, able to control various appliances and other equipment with high-current current.
  • Standard interface that can be controlled directly by microcontroller (Arduino, 8051, AVR, PIC, DSP, ARM, ARM, MSP430, TTL logic).
  • Indication LEDs for Relay output status.
  • With a normally-open (NO) and a normally-close (NC) contact.


  • Number of Relays: 4
  • Control signal: TTL level (Active Low)
  • Rated load: 7A/250VAC; 10A/125VAC; 10A/28VDC;
  • Contact action time: 10ms/5ms
  • Current: 15-20mA per channel




Pin definition


  • COM - Common pin: This is source pin, that starts connected to NC, and connects to NO when you apply 0v / GND (active low)
  • NC (Normally Closed): in which case NC is connected with COM when INT1 is set low and disconnected when INT1 is high;
  • NO (Normally Open): in which case NO is disconnected with COM1 when INT1 is set low and connected when INT1 is high.
  • INT 1- Relay 1 control port: changes from the COM–>NO to the COM–>NC when you apply 0v / GND (active low)
  • INT 2- Relay 2 control port: changes from the COM à NO to the COM à NC when you apply 0v / GND (active low)


Relay Module tutorial

Above: Example of connecting power and lights to a relays COM and NO connectors.  


The Sketch

Enter the following sketch, upload it and go to town.
If you open your Arduino serial monitor you will be able to see the progress.

// Basic 4 Realy board connection
// Each relay is turned on for 2 seconds and then off.
// You can here them click as there state changes from off to on and on to off.
// You will also see the corresponding Red LED on the 4 Relay board light up when the relay is on.
// Define names for the 4 Digital pins On the Arduino 7,8,9,10
// These data pins link to 4 Relay board pins IN1, IN2, IN3, IN4

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

void setup(){    
// Initialise the Arduino data pins for OUTPUT
  pinMode(RELAY1, OUTPUT);       
  pinMode(RELAY2, OUTPUT);
  pinMode(RELAY3, OUTPUT);
  pinMode(RELAY4, OUTPUT);

void loop(){
   digitalWrite(RELAY1,LOW);           // Turns ON Relays 1
   delay(2000);                                      // Wait 2 seconds
   digitalWrite(RELAY1,HIGH);          // Turns Relay Off

   digitalWrite(RELAY2,LOW);           // Turns ON Relays 2
   delay(2000);                                      // Wait 2 seconds
   digitalWrite(RELAY2,HIGH);          // Turns Relay Off

   digitalWrite(RELAY3,LOW);           // Turns ON Relays 3
   delay(2000);                                      // Wait 2 seconds
   digitalWrite(RELAY3,HIGH);          // Turns Relay Off

   digitalWrite(RELAY4,LOW);           // Turns ON Relays 4
   delay(2000);                                      // Wait 2 seconds
   digitalWrite(RELAY4,HIGH);          // Turns Relay Off        


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