Arduino Nano - Door Sensor - Relay

This tutorial instructs you how to use the Arduino Nano and door sensor to control the relay. By connecting the relay to a soleniod lock, light bulb, LED strip, motor, or actuator..., we can use a door sensor to control the them. We will learn two different applications:

Application 1 - The relay is activated when door is open and the relay is deactivated when door is closed. The relay state is synchronized with the door sensor state. In detail:

Application 2 - The relay state is toggled each time the door is opened. More specifically:

Hardware Preparation

1×Arduino Nano
1×USB A to Mini-B USB cable
1×Door Sensor
1×Relay
1×Breadboard
1×Jumper Wires
1×(Optional) Solenoid Lock
1×(Optional) 12V Power Adapter
1×(Optional) DC Power Jack
1×(Optional) 9V Power Adapter for Arduino Nano
1×(Recommended) Screw Terminal Adapter for Arduino Nano

Or you can buy the following sensor kit:

1×DIYables Sensor Kit 30 types, 69 units
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Overview of Relay and Door Sensor

If you are unfamiliar with relay and door sensor (including pinout, operation, and programming), the following tutorials can help:

Wiring Diagram

The wiring diagram between Arduino Nano and door sensor relay

This image is created using Fritzing. Click to enlarge image

Application 1 - The relay state is in sync with the door sensor state

Arduino Nano Code

/* * This Arduino Nano code was developed by newbiely.com * * This Arduino Nano code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/arduino-nano/arduino-nano-door-sensor-relay */ #define DOOR_SENSOR_PIN 5 // The Arduino Nano pin connected to the door sensor's pin #define RELAY_PIN 2 // The Arduino Nano pin connected to the relay module int door_state; void setup() { Serial.begin(9600); // Initialize the Serial to communicate with the Serial Monitor. pinMode(DOOR_SENSOR_PIN, INPUT_PULLUP); // set arduino pin to input pull-up mode pinMode(RELAY_PIN, OUTPUT); // set arduino pin to output mode } void loop() { door_state = digitalRead(DOOR_SENSOR_PIN); // read state if (door_state == HIGH) { Serial.println("The door is open"); digitalWrite(RELAY_PIN, HIGH); // turn on relay } else { Serial.println("The door is closed"); digitalWrite(RELAY_PIN, LOW); // turn off relay } }

Detailed Instructions

  • Connect an Arduino Nano to your computer with a USB cable.
  • Launch the Arduino IDE, and select the correct board and port.
  • Copy the code and open it in the Arduino IDE.
  • Click the Upload button on the Arduino IDE to compile and upload the code to the Arduino Nano.
Arduino IDE Upload Code
  • Open and close the door
  • Check out the change in the relay's condition.

You will see that the relay state is in sync with the door sensor state.

Code Explanation

Check out the line-by-line explanation contained in the comments of the source code!

Application 2 - Door Sensor toggles Relay

Arduino Nano Code - Door Sensor toggles Relay

/* * This Arduino Nano code was developed by newbiely.com * * This Arduino Nano code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/arduino-nano/arduino-nano-door-sensor-relay */ #define DOOR_SENSOR_PIN 5 // The Arduino Nano pin connected to the door sensor's pin #define RELAY_PIN 2 // The Arduino Nano pin connected to the relay module int relay_state = LOW; // The current state of relay int prev_door_state; // The previous state of door sensor int door_state; // The current state of door sensor void setup() { Serial.begin(9600); // Initialize the Serial to communicate with the Serial Monitor. pinMode(DOOR_SENSOR_PIN, INPUT_PULLUP); // set arduino pin to input pull-up mode pinMode(RELAY_PIN, OUTPUT); // set arduino pin to output mode door_state = digitalRead(DOOR_SENSOR_PIN); } void loop() { prev_door_state = door_state; // save the last state door_state = digitalRead(DOOR_SENSOR_PIN); // read new state if (prev_door_state == HIGH && door_state == LOW) { // state change: HIGH -> LOW Serial.println("The door-closing event is detected"); // toggle state of relay relay_state = !relay_state; // control relay according to the toggled state digitalWrite(RELAY_PIN, relay_state); } }

Code Explanation

You can locate the explanation in the comment lines of the Arduino Nano code above.

In the code, the expression relay_state = !relay_state is equivalent to the following code:

if(relay_state == LOW) relay_state = HIGH; else relay_state = LOW;

Detailed Instructions

  • Copy the code and open it in the Arduino IDE.
  • Upload the code to the Arduino Nano.
  • Open and close the door several times.
  • Check out the change in the relay's state.

You'll notice that the relay will switch on or off one time whenever you close the door.

Video Tutorial