![\"\"](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2019\/01\/guide-relay-module-arduino-featured.jpg?resize=1200%2C675&quality=100&strip=all&ssl=1\")
<\/p>\nThis article shows how to control mains voltage with the Arduino using a relay module. We make a brief introduction to the relay module and build a simple project example with the Arduino. The example we’ll build shows how to control a relay module with an Arduino and a PIR motion sensor.<\/p>\n
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By the end of this tutorial, you should be able to control any electronics appliances with your Arduino using a relay module.<\/p>\n
A relay is an electrically operated switch that can be turned on or off, letting the current go through or not, and can be controlled with low voltages, like the 5V provided by the Arduino pins.<\/p>\n
Controlling a relay module with the Arduino is as simple as controlling any other output as we’ll see later on.<\/p>\n
![\"relay-module\"](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2016\/11\/relay-module.jpg?resize=210%2C197&quality=100&strip=all&ssl=1\")
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This relay module has two channels (those blue cubes). There are other models with one, four and eight channels. This module should be powered with 5V, which is appropriate to use with an Arduino. There are other relay modules that are powered using 3.3V, which is ideal for ESP32, ESP8266, and other microcontrollers.<\/p>\n
Get a relay module<\/strong>:<\/p>\n The following figure shows the relay module pinout.<\/p>\n The six pins on the left side of the relay module connect high voltage, and the pins on the right side connect the component that requires low voltage\u2014the Arduino pins.<\/p>\n The high-voltage side has two connectors, each with three sockets: common (COM), normally closed (NC), and normally open (NO).<\/p>\n If you just want to light up a lamp occasionally, it is better to use a normally-open circuit configuration.<\/p>\n The low-voltage side has a set of four pins and a set of three pins.<\/p>\n The set at the right consists of VCC<\/strong> and GND<\/strong> to power up the module, and input 1 (IN1<\/strong>) and input 2 (IN2<\/strong>) to control the bottom and top relays, respectively.<\/p>\n The second set of pins consists of GND<\/strong>, VCC<\/strong>, and JD-VCC<\/strong> pins. The JD-VCC pin powers the electromagnet of the relay.<\/p>\n Note: <\/strong> notice that the module has a jumper cap connecting the VCC and JD-VCC pins; the one shown here is blue, but yours may be a different color. The jumper cap allows you to choose whether the circuit is physically connected to the Arduino circuit or not, and you can choose to have it on or not. With the jumper cap on, the VCC and JD-VCC pins are connected. That means the relay electromagnet is directly powered from the Arduino\u2019s power pin, so the relay module and the Arduino circuits are not physically isolated from each other (this is the configuration we’ll use). Without the jumper cap, you need to provide an independent power source to power up the relay\u2019s electromagnet through the JD-VCC pin. That configuration physically isolates the relays from the Arduino with the module\u2019s built-in optocoupler.<\/p>\n The connections between the relay module and the Arduino are really simple:<\/p>\n In this example, we create a motion sensitive lamp. A lamp lights up for 10 seconds every time motion is detected.<\/p>\n Motion will be detected using a PIR motion sensor<\/a>. If you are not familiar with the PIR motion sensor, you can read the following post:<\/p>\n To control the lamp with mains voltage we’ll use a relay module<\/a> in normally-open configuration.<\/p>\n Before proceeding with this project, I want to let you know that you\u2019re dealing with mains voltage. Please read the safety warning below carefully.<\/p>\n Warning: <\/strong> when you are making projects that are connected to mains voltage, you really need to know what you are doing, otherwise you may shock yourself. This is a serious topic, and we want you to be safe. If you’re not 100% sure what you are doing, do yourself a favor and don’t touch anything. Ask someone who knows!<\/p>\n Here’s the needed parts for this example:<\/p>\n You can use the preceding links or go directly to MakerAdvisor.com\/tools<\/a> to find all the parts for your projects at the best price!<\/p> Copy the following code to your Arduino IDE and upload it to your Arduino board.<\/p>\n Warning: <\/strong> you shouldn’t upload new code while your Arduino is connected to the relay.<\/p>\n View raw code<\/a><\/p>\n First, we create variables to hold the pin the relay IN1 pin is connected to and to save the relay state:<\/p>\n The PIR motion sensor is connected to pin 2<\/span>:<\/p>\n We need to create some auxiliary variables to handle timers with the PIR motion sensor. The lastDebounceTime<\/span> variable saves the last time motion was detected. The debounceDelay<\/span> saves how much time the lamp should remain on after motion is detected (here we’re setting 10 seconds = 10000 milliseconds)<\/p>\n In the setup()<\/span>, we set the relay as an OUTPUT and turn it off by default:<\/p>\n Because we’re using a normally open configuration, there is no contact between the COM and NO sockets unless you trigger the relay. The relay is triggered when the input goes below about 2 V. That means if you send a LOW signal from the Arduino, the relay turns on, and if you send a HIGH signal, the relay turns off; it works with inverted logic.<\/p>\n Set the PIR motion sensor as an interrupt:<\/p>\n Whenever the PIR motion sensor is triggered, it calls the detectMotion()<\/span> function declared at the end of the code to turn the relay on:<\/p>\n In the loop()<\/span>, we check whether 10 seconds have passed since the relay is on. If that condition is true, we can turn the relay off.<\/p>\n Assemble all the parts as shown in the schematic diagram.<\/p>\n Warning: <\/strong>do not touch any wires that are connected to mains voltage. Also make sure you have tighten all screws of the relay module.<\/p>\n The lamp is connected to the relay using a normally open configuration. The Arduino controls the relay through pin 8<\/span> (pin 8<\/span> is connected to the relay IN1 pin). Finally, the PIR motion sensor is connected to pin 2<\/span>.<\/p>\n After uploading the code and wiring the circuit, you can test your setup.<\/p>\n When motion is detected, your lamp lights up. If there isn’t motion for 10 seconds, the lamp turns off.<\/p>\n Controlling a relay module with the Arduino is as simple as controlling an output – you just need to send HIGH or LOW signals using an Arduino digital pin. With the relay module you can control almost any AC electronics appliances (not just lamps).<\/p>\n We hope you’ve found this guide useful. If you like this project, you may also like our premium Arduino course:<\/p>\n We have more than 60 free tutorials and projects with the Arduino. If you’re looking for a guide for a specific module, we probably have what you’re looking for.<\/p>\n\n
Relay Pinout<\/h2>\n
![\"\"](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2016\/12\/relay-module-pinout.jpg?resize=712%2C310&quality=100&strip=all&ssl=1\")
<\/p>\nMains voltage connections<\/h2>\n
![\"relay-labeled\"](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2016\/11\/relay-labeled.jpg?resize=372%2C342&quality=100&strip=all&ssl=1\")
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Pin wiring<\/h2>\n
![\"img_6361\"](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2016\/11\/IMG_6361.jpg?resize=395%2C425&quality=100&strip=all&ssl=1\")
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Example: Controlling a Lamp with a Relay Module and PIR Motion Sensor<\/h2>\n
![\"dsc09897\"](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2016\/11\/DSC09897.jpg?resize=473%2C382&quality=100&strip=all&ssl=1\")
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Safety warning<\/h2>\n
Parts required<\/h3>\n
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![](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2017\/10\/header-200.png?w=1200&quality=100&strip=all&ssl=1\")
<\/a><\/p>\nCode<\/h3>\n
\/*********\n Rui Santos\n Complete project details at http:\/\/randomnerdtutorials.com \n*********\/\n\n\/\/ Relay pin is controlled with D8. The active wire is connected to Normally Closed and common\nint relay = 8;\nvolatile byte relayState = LOW;\n\n\/\/ PIR Motion Sensor is connected to D2.\nint PIRInterrupt = 2;\n\n\/\/ Timer Variables\nlong lastDebounceTime = 0; \nlong debounceDelay = 10000;\n\nvoid setup() {\n \/\/ Pin for relay module set as output\n pinMode(relay, OUTPUT);\n digitalWrite(relay, HIGH);\n \/\/ PIR motion sensor set as an input\n pinMode(PIRInterrupt, INPUT);\n \/\/ Triggers detectMotion function on rising mode to turn the relay on, if the condition is met\n attachInterrupt(digitalPinToInterrupt(PIRInterrupt), detectMotion, RISING);\n \/\/ Serial communication for debugging purposes\n Serial.begin(9600);\n}\n\nvoid loop() {\n \/\/ If 10 seconds have passed, the relay is turned off\n if((millis() - lastDebounceTime) > debounceDelay && relayState == HIGH){\n digitalWrite(relay, HIGH);\n relayState = LOW;\n Serial.println("OFF");\n }\n delay(50);\n}\n\nvoid detectMotion() {\n Serial.println("Motion");\n if(relayState == LOW){\n digitalWrite(relay, LOW);\n }\n relayState = HIGH; \n Serial.println("ON");\n lastDebounceTime = millis();\n}\n<\/code><\/pre>\n\tHow the code works<\/h4>\n
int relay = 8;\nvolatile byte relayState = LOW;<\/code><\/pre>\nint PIRInterrupt = 2;<\/code><\/pre>\nlong lastDebounceTime = 0;\nlong debounceDelay = 10000;<\/code><\/pre>\npinMode(relay, OUTPUT);\ndigitalWrite(relay, HIGH);<\/code><\/pre>\npinMode(PIRInterrupt, INPUT);\n\/\/ Triggers detectMotion function on rising mode to turn the relay on, if the condition is met\nattachInterrupt(digitalPinToInterrupt(PIRInterrupt), detectMotion, RISING);<\/code><\/pre>\nvoid detectMotion() {\n Serial.println(\"Motion\");\n if(relayState == LOW){\n digitalWrite(relay, LOW);\n }\n relayState = HIGH;\n Serial.println(\"ON\");\n lastDebounceTime = millis();\n}<\/code><\/pre>\nif((millis() - lastDebounceTime) > debounceDelay && relayState == HIGH){\n digitalWrite(relay, HIGH);\n relayState = LOW;\n Serial.println(\"OFF\");\n}<\/code><\/pre>\nSchematic<\/h3>\n
![\"schematics\"](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2016\/11\/Schematics.png?resize=700%2C466&quality=100&strip=all&ssl=1\")
<\/a><\/p>\nDemonstration<\/h2>\n
![\"relay-module-gif\"](\"https:\/\/i0.wp.com\/randomnerdtutorials.com\/wp-content\/uploads\/2016\/11\/relay-module-gif.gif?resize=480%2C270&quality=100&strip=all&ssl=1\")
<\/p>\nWrapping Up<\/h2>\n
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