SENSORS/ACTUATORS

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 kits:

1	×	DIYables Sensor Kit (30 sensors/displays)
1	×	DIYables Sensor Kit (18 sensors/displays)

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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

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

Learn More

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