Raspberry Pi - Button Control Electromagnetic Lock

The tutorial instructs you how to use an Raspberry Pi and a button to control an electromagnetic lock. When the button is pressed, Raspberry Pi deactivates the electromagnetic lock for a predefined time (e.g. 10 seconds) to unlock the door. After that, the electromagnetic lock will be activated again to lock the door.

Hardware Preparation

1×Raspberry Pi 4 Model B
1×Electromagnetic Lock
1×Relay
1×12V Power Adapter
1×DC Power Jack
1×Push Button
1×(Optional) Panel-mount Push Button
1×Breadboard
1×Jumper Wires
1×(Optional) Screw Terminal Adapter for Raspberry Pi

Or you can buy the following sensor kit:

1×DIYables Sensor Kit 30 types, 69 units
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Overview of Button and Electromagnetic Lock

If you are unfamiliar with electromagnetic locks and buttons (including pinout, operation, and programming information), the following tutorials can help:

Wiring Diagram

The wiring diagram between Raspberry Pi and Button Electromagnetic Lock

This image is created using Fritzing. Click to enlarge image

Raspberry Pi Code - Button Controls Electromagnetic Lock Without Debouncing

Detailed Instructions

  • Make sure you have Raspbian or any other Raspberry Pi compatible operating system installed on your Pi.
  • Make sure your Raspberry Pi is connected to the same local network as your PC.
  • Make sure your Raspberry Pi is connected to the internet if you need to install some libraries.
  • If this is the first time you use Raspberry Pi, See how to set up the Raspberry Pi
  • Connect your PC to the Raspberry Pi via SSH using the built-in SSH client on Linux and macOS or PuTTY on Windows. See to how connect your PC to Raspberry Pi via SSH.
  • Make sure you have the RPi.GPIO library installed. If not, install it using the following command:
sudo apt-get update sudo apt-get install python3-rpi.gpio
  • Create a Python script file button_electromagnetic_lock.py and add the following code:
# This Raspberry Pi code was developed by newbiely.com # This Raspberry Pi code is made available for public use without any restriction # For comprehensive instructions and wiring diagrams, please visit: # https://newbiely.com/tutorials/raspberry-pi/raspberry-pi-button-control-electromagnetic-lock import RPi.GPIO as GPIO import time BUTTON_PIN = 18 # GPIO pin connected to the button RELAY_PIN = 16 # GPIO pin controlled the electromagnetic lock via the relay module # Set up the GPIO pins GPIO.setmode(GPIO.BCM) GPIO.setup(BUTTON_PIN, GPIO.IN, pull_up_down=GPIO.PUD_UP) GPIO.setup(RELAY_PIN, GPIO.OUT) prev_button_state = GPIO.HIGH # HIGH means the button is not pressed initially try: # Lock the door initially GPIO.output(RELAY_PIN, GPIO.HIGH) while True: button_state = GPIO.input(BUTTON_PIN) if button_state == GPIO.LOW and prev_button_state == GPIO.HIGH: # Button is pressed (LOW means pressed due to pull-up resistor) print("The button is pressed") GPIO.output(RELAY_PIN, GPIO.LOW) # Unlock the door print("The door is unlocked") time.sleep(5) # Wait for 5 seconds GPIO.output(RELAY_PIN, GPIO.HIGH) # Lock the door again print("The door is locked again") # Update the previous button state prev_button_state = button_state except KeyboardInterrupt: print("Exiting...") GPIO.cleanup()
  • Save the file and run the Python script by executing the following command in the terminal:
python3 button_electromagnetic_lock.py
  • Bring the armature plate close to the electromagnet.
  • Press the button once.
  • Check out the attraction between the armature plate and the electromagnet for 10 seconds.

The script runs in an infinite loop continuously until you press Ctrl + C in the terminal.

Code Explanation

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

Video Tutorial