Interfacing Relay boards to Arduino

This post is intended for beginners to interface relay boards with Arduino. Shown below is the connection details to connect 4 Channel relay board with Arduino. The relays are 12V relays.

RELAY 4_Watermark

The details of the 4 channel relay board is given below.

4Channel Relay_Watermark

• Connect VCC to 12V.
• Inputs 1,2,3 & 4 are used to control the corresponding relays.
• If input is high (5V), then connection is between C (Common) & NO (Normally Open), else connection is between C (Common) & NC (Normally Closed).
• If Input1 is high, LED1 glows and vice versa.
• This board has a ULN driver which gives better performance compared to transistor drive.
• ULN2003 has seven high current Darlington arrays each containing seven open collector Darlington pairs with common emittors.
PS : Make sure to short the ground of 12V and Arduino.

Given below is a sample code to operate the 4 channel relay board using Arduino.

Depending on the state of the pushbutton connected to pin 7 relays will be turned ON/OFF. If pin 7 is high, relays will be turned ON and vice versa.

// constants won’t change. They’re used here to
// set pin numbers:
const int buttonPin = 7; // the number of the pushbutton pin
const int relay1 = 2; // the number of the relay1 pin
const int relay2 = 3;
const int relay3 = 4;
const int relay4 = 5;// variables will change:
int buttonState = 0; // variable for reading the pushbutton status

void setup() {
// initialize the relay1,2,3,4 pins as an output:
pinMode(relay1, OUTPUT);
pinMode(relay2, OUTPUT);
pinMode(relay3, OUTPUT);
pinMode(relay4, OUTPUT);
// initialize the pushbutton pin as an input:
pinMode(buttonPin, INPUT);
}

void loop(){
// read the state of the pushbutton value:
buttonState = digitalRead(buttonPin);

// check if the pushbutton is pressed.
// if it is, the buttonState is HIGH:
if (buttonState == HIGH) {
// turn relays on:
digitalWrite(relay1, HIGH);
digitalWrite(relay2, HIGH);
digitalWrite(relay3, HIGH);
digitalWrite(relay4, HIGH);
}
else {
// turn relays off:
digitalWrite(relay1, LOW);
digitalWrite(relay2, LOW);
digitalWrite(relay3, LOW);
digitalWrite(relay4, LOW);
}
}

 

Likewise the details of Single channel, 2-channel and 8-Channel relay boards are given below.
Single Channel Relay board.
RELAY 1_WatermarkGiven below is a sample code to operate the single channel lay board using Arduino.

 

// constants won’t change. They’re used here to
// set pin numbers:
const int buttonPin = 7; // the number of the pushbutton pin
const int relay1 = 13; // the number of the relay1 pin// variables will change:
int buttonState = 0; // variable for reading the pushbutton status

void setup() {
// initialize the relay pin as an output:
pinMode(relay1, OUTPUT);
// initialize the pushbutton pin as an input:
pinMode(buttonPin, INPUT);
}

void loop(){
// read the state of the pushbutton value:
buttonState = digitalRead(buttonPin);

// check if the pushbutton is pressed.
// if it is, the buttonState is HIGH:
if (buttonState == HIGH) {
// turn relays on:
digitalWrite(relay1, HIGH);

}
else {
// turn relays off:
digitalWrite(relay1, LOW);

}
}

Single channel relay_Watermark
2 Channel relay board
RELAY 2_Watermark

Given below is a sample code to operate the 2 channel lay board using Arduino.

// constants won’t change. They’re used here to
// set pin numbers:
const int buttonPin = 7; // the number of the pushbutton pin
const int relay1 = 12; // the number of the relay1 pin
const int relay2 = 13;// variables will change:
int buttonState = 0; // variable for reading the pushbutton status

void setup() {
// initialize the relay1,2 pins as an output:
pinMode(relay1, OUTPUT);
pinMode(relay2, OUTPUT);
// initialize the pushbutton pin as an input:
pinMode(buttonPin, INPUT);
}

void loop(){
// read the state of the pushbutton value:
buttonState = digitalRead(buttonPin);

// check if the pushbutton is pressed.
// if it is, the buttonState is HIGH:
if (buttonState == HIGH) {
// turn relays on:
digitalWrite(relay1, HIGH);
digitalWrite(relay2, HIGH);
}
else {
// turn relays off:
digitalWrite(relay1, LOW);
digitalWrite(relay2, LOW);
}
}

2Channel relay_Watermark
8 Channel Relay board
RELAY 8_Watermark

 

Given below is a sample code to operate the 8 channel relay board using Arduino.

// constants won’t change. They’re used here to
// set pin numbers:
const int buttonPin = 8; // the number of the pushbutton pin
const int relay1 = 0; // the number of the relay1 pin
const int relay2 = 1;
const int relay3 = 2;
const int relay4 = 3;
const int relay5 = 4;
const int relay6 = 5;
const int relay7 = 6;
const int relay8 = 7;// variables will change:
int buttonState = 0; // variable for reading the pushbutton status

void setup() {
// initialize the relay1,2,3,4 pins as an output:
pinMode(relay1, OUTPUT);
pinMode(relay2, OUTPUT);
pinMode(relay3, OUTPUT);
pinMode(relay4, OUTPUT);
pinMode(relay5, OUTPUT);
pinMode(relay6, OUTPUT);
pinMode(relay7, OUTPUT);
pinMode(relay8, OUTPUT);
// initialize the pushbutton pin as an input:
pinMode(buttonPin, INPUT);
}

void loop(){
// read the state of the pushbutton value:
buttonState = digitalRead(buttonPin);

// check if the pushbutton is pressed.
// if it is, the buttonState is HIGH:
if (buttonState == HIGH) {
// turn relays on:
digitalWrite(relay1, HIGH);
digitalWrite(relay2, HIGH);
digitalWrite(relay3, HIGH);
digitalWrite(relay4, HIGH);
digitalWrite(relay5, HIGH);
digitalWrite(relay6, HIGH);
digitalWrite(relay7, HIGH);
digitalWrite(relay8, HIGH);
}
else {
// turn relays off:
digitalWrite(relay1, LOW);
digitalWrite(relay2, LOW);
digitalWrite(relay3, LOW);
digitalWrite(relay4, LOW);
digitalWrite(relay5, LOW);
digitalWrite(relay6, LOW);
digitalWrite(relay7, LOW);
digitalWrite(relay8, LOW);
}
}

 

8Channel Relay board_Watermark
• Connect VCC to 12V.
• Inputs 1 to 8 are used to control the corresponding relays.
• If input is high(5V) , then connection is between C (Common) & NO (Normally Open), else connection is between C (Common) & NC (Normally Closed).
• If Input1 is high, LED1 glows and vice versa.
• Provision is left for connecting AC supply.
• This board has a ULN driver which gives better performance compared to transistor drive.
• The ULN2803A device is a high-voltage, high-current Darlington transistor array. The device consists of eight npn Darlington pairs that feature high-voltageoutputs with common-cathode clamp diodes for switching inductive loads.

 

The above products can be purchased from this link.

Sample codes can be downloaded from this link

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21 thoughts on “Interfacing Relay boards to Arduino

  1. Dear Sir Thank you very much for detailed description. Its too good. But my question is I want to use reed switch / magnetic switch & PIR sensor as input and audio alarm and sms/call alert as output. Someone told me that for such input purpose, I has to use relay module. Is it true? If yes then how to connect 16 relays (8 relay board X 2) as input? How to code it?

    • Relay modules are used for output controlling. For example if you are using your microcontroller to switch a 230 volt appliance you need relay in between along with the driver circuit to operate the relays. For 16 channel you may need to use a0 to a5 pins of arduino also along with other digital output pin. Sample program can be modified according to your need .

  2. For the 4 channel 12 V relay . The relay is switching when digital o/p from arduino is high,but when the digital output is made low the relay isn’t switching back to its normal condition.Why?
    NB:Though there is noticeable change in LEDs when digital outputs are changed.

    • Hello Ajas,
      Try connecting 5 V vcc and ground from the arduino board and see if the relay is working fine. It seems that you haven’t defined the pin connected to relay as output. Please see if you have called the pinmode function to define the call as output.

  3. I have bought 4 Channel relay board (above) but it does not seems to be working.. 😦 i have one question though .. can we use a 12v power adapter to power it… I have cut my power adapter tail and using the two wires to power my board through vcc and gnd respectively.. but its not working.. pls help… or do i need a 12v battery to power it on??? does it works only on battery??

    • Please use adaptor of rating 12V and 1Ampere or more. Relay will work with both power adapter or battery, provided it should be giving sufficient current to relay coils. Use a multimeter to ensure proper contacts is made with the connections.

      • Thank You for the reply… i have my circuit done properly with right power ratings and stuff.. but somehow it still not working.. maybe my relay board is defective.. what actually happens is that as i complete my circuit and connect the + termimal to vcc the leds slightly lit up and then again go off.. what might be the reason for that?? and when i load the program to arduino to run my board it does nothing… stares me idiotically point blank @ my face… 😦

  4. hi i am using a 8 ch relay which i am trying to get it working with a arduino mega.i have a 12vdc 1A adapter but the thing wont trigger the relay….i have couple of questions hope that some one can help me here.
    Q1. vcc is given 12vdc but the ground is given from board or the adapter negative itself?
    Q2 or are all the gnd to be grounded together I.e arduino gnd relay gnd and adapter gnd?
    i hope my queries will be answered soon thanking in advance.

  5. I have bought 2 Channel relay board but its not working because of uncommon neutral.
    Please explain me how to short neutral of 2 different source ,and will it effect the circuit?
    I connected arduino with usb cable(which have its own neutral),relay powered by external 12v dc source (which have its own neutral).so if i short all neutral and connected to arduino gnd pin will it damage the circuit.

  6. How to connect 4 channel 12v relay using single adaptor for both relay module and Arduino.
    When I contacted the same it’s can’t working…
    Relay indicater LED glow during low brightness. What is the mistake in my connections please give me suggestions…

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