🔐 Control a Solenoid Lock with Arduino Mega (Using a Relay & Push Button)

Introduction

Welcome back, makers! 👋
If you enjoyed building Wi-Fi-controlled LEDs, let’s take things a step further into the world of physical security. Today, we’re working with solenoid locks — the same mechanism used in lockers, cabinets, and access-control systems.

In this project, you’ll learn how to lock and unlock a solenoid lock using:

1. 1. Arduino Mega
2. 2. A relay module
3. 3. 12V power supply
4. 4. Simple push button
5. Breadboard
6. Jumper wires(male to male and male to female)

• By the end, you’ll push a button → the solenoid will pull → the lock will OPEN.
• Push the button again → the solenoid releases → the lock goes back to LOCKED.

Let’s dive in!

🧰 What You’ll Need

Component	Image	Description
Arduino Mega		Microcontroller to read button and control relay
12V Solenoid Lock		The physical locking mechanism
Relay Module (5V Control)		Acts as a switch to send 12V to the solenoid
12V Power Adapter		Powers the solenoid and Arduino
Push Button		Triggers lock/unlock
Breadboard & Jumper Wires		For easy wiring

⚡ Step 1: Wiring Diagram

Here’s the wiring logic broken down clearly:

🔘 Button to Arduino

Component	Arduino Pin	Purpose
Button Lead 1	D2	Reads button press
Button Lead 2	GND	Completes button circuit

🔁 Relay Module to Arduino

Component	Arduino Pin	Purpose
VCC	5V	Powers relay coil
GND	GND	Ground
IN	D8	Arduino signal to toggle solenoid

🔌 Power + Solenoid Connection

Component	Connected To	Purpose
12V Adapter	Arduino Barrel Jack	Powers Arduino and relay
12V Adapter + (Positive)	Relay COM	12V source for switching
Solenoid Red Wire	Relay NO	Receives switched 12V
Solenoid Blue Wire	GND	Completes 12V circuit

💡 We use the relay because the solenoid draws more current than Arduino can provide.

💻 Step 2: Write the Code

Open your Arduino IDE and paste the following code:

// Define the pins used
const int buttonPin = 2;   
const int relayPin = 8;    

bool isLocked = true; 

void setup() {
  pinMode(relayPin, OUTPUT); 
  // Use INPUT_PULLUP for simpler button wiring
  pinMode(buttonPin, INPUT_PULLUP); 

  // SET INITIAL STATE: LOCK the door (Solenoid needs POWER ON to be locked)
  digitalWrite(relayPin, HIGH); 
}

void loop() {
  // Read the button state (it reads LOW when pressed)
  int buttonState = digitalRead(buttonPin);

  if (buttonState == LOW) { // Button pressed
    delay(50); // Debounce
    if (digitalRead(buttonPin) == LOW) {
      isLocked = !isLocked; // Toggle the state

      if (isLocked) {
        // LOCK: Solenoid ON (Power applied)
        digitalWrite(relayPin, HIGH); 
      } else {
        // UNLOCK: Solenoid OFF (Power removed)
        digitalWrite(relayPin, LOW); 
      }

      // Wait for the button to be released 
      while(digitalRead(buttonPin) == LOW){
        // Do nothing 
      }
    }
  }
}

🧠 Explanation

• The button uses INPUT_PULLUP, meaning:
  • Released → HIGH
  • Pressed → LOW
• When pressed, Arduino sets relay HIGH → relay sends 12V to solenoid → it unlocks.
• When pushed again → relay turns OFF → the solenoid locks again.

🧪 Step 3: Test the Setup

1. Power the Arduino using your 12V adapter.
2. Open the Serial Monitor — you should see "Solenoid Lock System Ready".
3. Press the button:
   • You should hear a click from the relay.
   • Solenoid retracts (unlock).
4. Press the button again:
   • Solenoid extends (lock).

🔐⚡ If everything is wired correctly — congratulations, you’ve built your own electromechanical locking system!

Comments

[arumy56]

Nice tutorial which is easy to follow