2 Channel Relay Module : PinOut, Specifications, Components, Circuit, Interfacing, Working & Its Applications

A relay module is a simple circuit board that houses a minimum of one or more relays, and they come in different sizes and shapes. However, they are most commonly available in a rectangular shape with two, four, or eight, and up to 16 relays placed on them. These modules can also have protection diodes, indicator LEDs, resistors, transistors, etc. The primary function of the relay module is to switch electrical systems and devices on or off. In addition, it can also isolate the control circuit from the system or device being controlled. This article elaborates on the 2 channel relay module, its working, and its applications.

What is a 2 Channel Relay Module?

The dual-channel relay module is a convenient board that is similar to a single-channel relay module but with some additional features like optical isolation. Thus, this module can switch high-powered loads from the microcontroller pins like motors, lamps, AC loads, and solenoid valves. This module has three terminals like COM, NO & NC, and is being brought out through a screw terminal.

In addition, this module can also be available with an LED to specify the relay status. This module can be interfaced with different microcontrollers like Arduino, 8051, PIC, AVR, PIC, ARM, DSP, TTL logic, MSP430, etc. This module controls different appliances and other equipment through a large current.

2 Channel Relay Module Working

A 2-channel relay module works with control signals to switch high-power devices on or off from a microcontroller. Whenever a microcontroller sends a high or low signal to the IN1/IN2 input pins of the relay module, it activates the equivalent relay. So this relay module understands this signal to control the switching of the connected high-power device.

Every relay on this module includes three main contacts: Normally Open or NO, Normally Closed or NC, & Common or COM.

Whenever the relay is stationary, the COM and NO terminals will stay disconnected, and the COM and NC terminals will stay connected. Once the relay is triggered, the COM and NO terminals will be connected, which closes the circuit & allows current supply, while the COM and NC terminals disconnect.

2 Channel Relay Module Pin Diagram

The channel relay module includes thirteen pins, which are separated into control pins, power supply selection pins, and output terminals.

Control Pins

The two-channel relay module control pins mainly include IN1 & IN2, VCC, and GND, which are explained below.

• The VCC pin of this module provides a power supply to the integral optocouplers. So this can be connected to the 5Volts pin of the Arduino.
• The GND pin is the common ground of the module.=
• The IN1 and IN2 pins are used to control the relay. So these are known as active low pins, thus, it pulls them to LOW to activate the relay & pulls them to HIGH to deactivate it.

Power Supply Selection Pins

• The JD-VCC pin of this module supplies power to the electromagnet of the relay. Whenever the jumper is within position then this pin will be shorted to VCC. It allows the electromagnets of the module to be powered through the 5V line of the Arduino board.
• The VCC pin can be shorted to the JD-VCC pin through the jumper cap. This pin is disconnected if you eliminate the jumper.
• The GND terminal is the common ground pin.

Output Terminals

• The COM terminal of this module connects to the device you want to control.
• NC is normally connected to the COM terminal, except when you turn on the relay that breaks the connection.
• NO terminal is normally open, except when you trigger the relay that is connected to the COM terminal.

Features & Specifications:

The features and specifications of the 2-channel relay module include the following.

• Its voltage supply ranges from 3.75V to 6V
• The trigger current of this module is 5mA
• The current supply when the relay is active for single is ~70mA and for dual is ~140mA.
• Its maximum contact voltage of the relay is – 250VAC, 30VDC
• The maximum current of the relay is – 10A
• A freewheeling diode is used to guard your microcontroller
• It controls both AC & DC appliances like Motors, Solenoids, fans, lights, and many more.
• This module has high-quality screw terminals used for easy connection
• It includes two independent channels used for device control.
• The relay directly controls all types of load and equipment.
• Its power consumption is low for energy efficiency.
• This module is equipped with a high-current relay 10A at 250VAC or 10A at 30VDC.
• It has LED status indicators to point out the relay status
• Its operating temperature ranges from -40°C to +85°C.
• Its storage temperature ranges from -65°C to 125°C.

Equivalents and Alternatives

Equivalent relay channel modules are single-channel, dual-channel, four-channel, and eight-channel relay modules. Alternative relay modules for switching mainly include SCRs, solid-state relay modules, TRIACs etc.

Components

The two-channel relay module includes different components, which are explained below.

Relays

This relay module includes switching relays with drive circuitry, which makes it easy to incorporate relays into a project powered through a microcontroller. There are two terminal blocks on the left side, which are utilized to connect the mains wires to the relay module without any soldering. After that, two relays are marked on the body, the relay coil is rated for 5VDC & the contacts are simply rated for 10A at 250VAC (or) 30VDC, (or) 125VAC (or) 28VDC.

Input Block

The input block in this relay module is arranged on the right side. So this block has control pins above the higher right corner, whereas a power supply jumper is on the below right corner.

Control Pins

This block has four control pins like the Vcc pin is used to switch on the relay module, and two input pins and a GND pin are used for controlling relays correspondingly. Here Vcc pin provides a 5Volts supply to the module’s status LED.

Power Supply Selection Jumper

The selection jumper on this module shows that it allows us to choose whether we wish to power up the relay module with a microcontroller or an independent power source. If the relay is activated through a microcontroller, the blue color jumper cap should stay integral. Thus, this module is connected physically with the microcontroller.

To make this relay function, the elimination of the jumper cap instructs us to provide a separate power source with the JD-Vcc pin. Thus, the microcontroller in this way will not be connected physically to the circuit due to its in-built opto-isolators.

Output Block

The output block is available on the left side of the relay module that includes 2 pairs of 3-screw terminals like normally open (NO), normally closed (N.C) & common (C.O).

NO and NC Contacts

NC is a normally closed contact, and NO is a normally open contact. When the relay coil is de-energized, the normally closed contact will be opened & normally opened contact will be closed.

Status LEDs

The relay module has two SMD status LEDs. So, each relay has its status LED that allows it once its particular relay is made stronger throughout the input pin. Once it is a 5Volts dual channel module, the status LEDs will be harmed whenever the voltage is >5 volts.

Freewheeling Diodes

This module includes two freewheeling diodes, which are useful for controlling the back EMF generated by the relay’s inductive coils. This emf causes severe harm, thus, we require freewheeling diodes to oppose the effect.

Switching Transistors

The two-channel relay module has switching transistors, which increases the current supply to meet the requirement of the relays. Thus, these transistors help in controlling these relays with any ESP32, TM4C123, or Arduino microcontroller by using its low-current GPIO pins. The transistor type decides whether the input pins are active high or low.

Optoisolator ICs

These ICs in this module provide the right isolation among the DC Circuit & the power to dual supply relays to transmit the input signal without being associated directly.

2 Channel Relay Module Circuit with Optocoupler

The internal two-channel relay module circuit with an opto-coupler is shown below. There are many differences when compared with the single-channel relay module. So the first difference is the optocoupler & relay have a separate power supply using the input. This is chosen with the JD-VCC if the jumper is shorted; after that, the relay coil & optocoupler output are simply connected to the VCC signal. If this module’s jumper is left open, then a separate power supply is given to the relay coil with the JD-VCC pin.

The second difference is the active low input; thus, the relay coil is activated whenever the input is low. This is due to the optocoupler input and the indicator LED being connected to VCC. Once the input supply is high, voltage variation across the chain is zero volts, and there is no supply. Whenever the input is low, then the voltage supply will appear across the chain & the output of the optocoupler will conduct by supplying current to the drive transistor’s base and turning the relay on.

Interfacing Dual Channel Relay Module with Arduino Board

Relays are used in creative ways, such as DIY and electronics projects, which control the operation of motors, equipment, lights, etc. So one of the most intriguing and entertaining features of relays is, we can utilize them to mechanize and control a broad range of activities. These are used to cut off one electrical circuit from another. This maintains electronic devices against getting spoiled. A relay is frequently used to switch and control electrical circuits.

The interfacing 5V dual-channel relay module with the Arduino board is shown below. The required components to make this interfacing include a 5V 2-channel relay module, Arduino UNO, a switch, a bulb, a breadboard, and jumper wires. The connections of this relay module with Arduino are as;

• The IN1 pin of the relay module is connected to the D13 pin of Arduino Uno.
• The GND pin of the relay module is connected to the GND pin of the Arduino board.
• The VCC pin of the relay module is connected to the 5V pin of the Arduino board.
• Initially, Arduino IDE Software needs to be installed from the Arduino official website.

Code

The required 2-channel relay module Arduino code for interfacing with Arduino is shown below. Now copy the below code & upload it into Arduino IDE Software.

//the relays connect to
int IN1 = 13;
#define ON 0
#define OFF 1
void setup()
{
relay_init();//initialize the relay
}
void loop() {
relay_SetStatus(ON);//turn on RELAY_1
delay(2000);//delay 2s
relay_SetStatus(OFF);//turn off RELAY_1
delay(2000);//delay 2s
}
void relay_init(void)//initialize the relay
{
//set all the relays OUTPUT
pinMode(IN1, OUTPUT);
relay_SetStatus(OFF); //turn off all the relay
}
//set the status of relays
void relay_SetStatus( unsigned char status_1)
{
digitalWrite(IN1, status_1);
}

Working

To test the circuit, first need to upload the above code and notice the relay is turning on & off.

At first, we name the connected pin to pin-13.

The relay_init() function in the void setup initializes the relay by setting its pin as an output & turning it off.

We used the relay_SetStatus() frequently in the void loop() to activate and deactivate the relay with a two-second delay time between every call.

Both the relay_SetStatus() and relay_init() functions are defined codes used to initialize & control the relay.

The above program initializes the dual-channel relay by calling the relay_init() function; thus, it sets the pin of the relay as an output & it will turn off. After that, the code enters into the main loop, where it frequently turns on and off the relay for two seconds and again repeats. Thus, this can cause the connected electrical device to the relay to turn on & off.

How to Test 2 Channel Relay Modules?

A two-channel relay module can be tested with a multimeter to check for stability and resistance. After that, a power source needs to be used to test each relay’s switching functionality. A low-level signal from a microcontroller can also be used to activate every channel and monitor the equivalent LED indicator & connected load.

Test 2 Channel Relay Module with a Multimeter:

First, the multimeter needs to be set to resistance to measure the resistance between the two coil terminals of every relay channel. So a good coil must include some resistance; a zero reading (or) open line to indicate a faulty coil.

The millimeter probes need to be connected to the NO and COM terminals of every channel. So there must be no continuity with the de-energized relay. When the relay is energized then there must be continuity between the two NO and COM terminals.

Testing through a Power Source

The relay module must be connected to its power supply, like VCC & GND, to examine the power LED.
A low-level signal must be applied to every channel’s signal terminal.

Every channel must contain an equivalent LED to light up whenever the relay is triggered. :

A test load like an LED (or) a lamp needs to be connected to the NC, NO, or COM terminals of every channel. After that, monitor whether the load switches on & off as expected whenever the signal is provided & removed.

Thus, by following the above steps, the two-channel relay module can be tested thoroughly and make sure that it is working properly.

Applications

The applications of the dual-channel relay module include the following.

• Washing machines.
• Automobiles.
• Refrigerators.
• Electrical appliances.
• Industrial control systems.
• Switching mains loads.
• High current load switching.
• Battery backup.
• Home automation.

Please refer to this link for the 2-channel relay module datasheet.

Thus, this is about a 2-channel relay module that allows an Arduino board to control two separate high-voltage and high-current loads through a low-voltage signal. Every channel of this module works like an independent switch by allowing different devices to control it, like lights, solenoids, or motors. This module normally features a 5V control voltage to handle AC & DC loads with common 10A ratings at 30VDC or 250VAC. Here is a question for you: What is a relay?