Arduino - Button Control Electromagnetic Lock

The tutorial uses electromagnetic lock to unlock/lock the door, The code will includes two main parts:

When button is pressed, unlock the door for 10 seconds and then lock the door.

Hardware Required

1×Arduino UNO or Genuino UNO
1×USB 2.0 cable type A/B
1×Electromagnetic Lock
1×Relay
1×12V Power Adapter
1×Button
1×Breadboard
n×Jumper Wires
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About Button and Electromagnetic Lock

If you do not know about electromagnetic lock and button (pinout, how it works, how to program ...), learn about them in the following tutorials:

Wiring Diagram

Arduino Button Electromagnetic Lock Wiring Diagram

Image is developed using Fritzing. Click to enlarge image

Arduino Code - Button Controls Electromagnetic Lock Without Debouncing

/* * Created by ArduinoGetStarted.com * * This example code is in the public domain * * Tutorial page: https://arduinogetstarted.com/tutorials/arduino-button-controls-electromagnetic-lock */ // constants won't change const int BUTTON_PIN = 7; // Arduino pin connected to button's pin const int RELAY_PIN = 3; // Arduino pin connected to relay's pin // variables will change: int lastButtonState; // the previous state of button int currentButtonState; // the current state of button void setup() { Serial.begin(9600); // initialize serial pinMode(BUTTON_PIN, INPUT_PULLUP); // set arduino pin to input pull-up mode pinMode(RELAY_PIN, OUTPUT); // set arduino pin to output mode digitalWrite(RELAY_PIN, HIGH); // lock the door currentButtonState = digitalRead(BUTTON_PIN); } void loop() { lastButtonState = currentButtonState; // save the last state currentButtonState = digitalRead(BUTTON_PIN); // read new state if(lastButtonState == HIGH && currentButtonState == LOW) { Serial.println("The button is pressed"); digitalWrite(RELAY_PIN, LOW); // unlock the door in 10 seconds delay(10000); // 10 seconds digitalWrite(RELAY_PIN, HIGH); // lock the door again } }

Quick Steps

  • Connect Arduino to PC via USB cable
  • Open Arduino IDE, select the right board and port
  • Copy the above code and open with Arduino IDE
  • Click Upload button on Arduino IDE to upload code to Arduino
  • Put the armature plate close to electromagnet.
  • Press button one time.
  • See the attraction between armature plate and electromagnet during 10 seconds.

Code Explanation

Read the line-by-line explanation in comment lines of code!

※ NOTE THAT:

In practice, the above code does not work correctly sometimes. To make it always work correctly, we need to debounce for the button . Debouncing for the button is not easy for beginners. Fortunately, thanks to the ezButton library , We can do it easily.

Arduino Code - Button Controls Electromagnetic Lock With Debouncing

Why do we need debouncing? ⇒ see Arduino - Button Debounce tutorial

/* * Created by ArduinoGetStarted.com * * This example code is in the public domain * * Tutorial page: https://arduinogetstarted.com/tutorials/arduino-button-controls-electromagnetic-lock */ #include <ezButton.h> // constants won't change const int BUTTON_PIN = 7; // Arduino pin connected to button's pin const int RELAY_PIN = 3; // Arduino pin connected to relay's pin ezButton button(BUTTON_PIN); // create ezButton object that attach to pin 7; void setup() { Serial.begin(9600); // initialize serial pinMode(RELAY_PIN, OUTPUT); // set arduino pin to output mode button.setDebounceTime(50); // set debounce time to 50 milliseconds digitalWrite(RELAY_PIN, HIGH); // lock the door } void loop() { button.loop(); // MUST call the loop() function first if(button.isPressed()) { Serial.println("The button is pressed"); digitalWrite(RELAY_PIN, LOW); // unlock the door in 10 seconds delay(10000); // 10 seconds digitalWrite(RELAY_PIN, HIGH); // lock the door again } }

Quick Steps

  • Install ezButton library. See How To
  • Copy the above code and open with Arduino IDE
  • Click Upload button on Arduino IDE to upload code to Arduino
  • Put the armature plate close to electromagnet.
  • Press button one time.
  • See the attraction between armature plate and electromagnet during 10 seconds.

※ NOTE THAT:

In the above code, we used the delay function. Therefore, we do not need to debouncing for button. However, We still provide the code with debouncing just in case you want to do more tasks without using delay function. See How to use millis() instead of delay()

Video Tutorial

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Button and Electromagnetic Lock on Commercial Products

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