Arduino Mega - Solenoid Lock

This guide shows you how to use the Arduino Mega board and a solenoid lock to lock or unlock a door, cabinet, or drawer. Here is what we will learn:

How to connect a solenoid lock to an Arduino Mega.
How to write code for the Arduino Mega to control the solenoid lock.

Hardware Preparation

1	×	Arduino MEGA
1	×	Alternatively, DIYables MEGA Development Board
1	×	USB 2.0 cable type A/B (for USB-A PC)
1	×	USB 2.0 cable type C/B (for USB-C PC)
1	×	Solenoid Lock
1	×	Relay
1	×	12V Power Adapter
1	×	DC Power Jack
1	×	Recommended: Screw Terminal Block Shield for Arduino Uno/Mega
1	×	Recommended: Sensors/Servo Expansion Shield for Arduino Mega
1	×	Recommended: Breadboard Shield for Arduino Mega
1	×	Recommended: Enclosure for Arduino Mega

Or you can buy the following kits:

DIYables Sensor Kit (18 sensors/displays)

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Additionally, some of these links are for products from our own brand, DIYables .

Overview of Solenoid Lock

A solenoid lock, also called an electric strike lock, locks and unlocks cabinets, drawers, and doors.

Pinout

A solenoid lock uses two wires.

Connect the red wire (positive) to the 12V DC power supply.
Connect the black wire (negative) to the ground (GND) of the power supply.

How It Works

When the electric lock has power, the latch extends and the door is locked.
When there is no power, the latch retracts and the door is unlocked.

※ NOTE THAT:

The solenoid lock usually needs a power supply of 12V, 24V, or 48V. Do not connect the lock directly to an Arduino Mega pin. Instead, use a relay between the lock and the Arduino Mega pin.

If we connect the solenoid lock to a relay that is normally open:

If the switch is off, the door is unlocked.
If the switch is on, the door is locked.

Connect an Arduino Mega to a relay to control a solenoid lock. Learn more about using a relay with Arduino Mega in our guide: Arduino Mega - Relay Tutorial.

Wiring Diagram

This image is created using Fritzing. Click to enlarge image

Arduino Mega Code

This program locks and unlocks the door every five seconds.

/* * This Arduino Mega code was developed by newbiely.com * * This Arduino Mega code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/arduino-mega/arduino-mega-solenoid-lock */ #define RELAY_PIN 3 // The Arduino Mega pin connected to the IN pin of relay // the setup function runs once when you press reset or power the board void setup() { // initialize digital pin as an output. pinMode(RELAY_PIN, OUTPUT); } // the loop function runs over and over again forever void loop() { digitalWrite(RELAY_PIN, HIGH); // uhlock the door delay(5000); digitalWrite(RELAY_PIN, LOW); // lock the door delay(5000); }

Detailed Instructions

Follow these steps one by one.

Connect the solenoid lock to the Arduino Mega as shown in the diagram.
Connect the Arduino Mega to your computer with a USB cable.
Open the Arduino IDE on your computer.
Choose the correct board (Arduino Mega) and the right COM port.
Copy the code and open it in the Arduino IDE.
Click the Upload button in the Arduino IDE to send the code to the Arduino Mega.
Check the lock bolt position.

Relay vs MOSFET Module for the Solenoid Lock

This tutorial uses a relay to switch the solenoid lock. A 12V solenoid lock runs on DC, so a MOSFET module can also switch it.

	Relay	MOSFET Module
Lock control	lock or unlock	lock or unlock
Switching sound	a click every time	no sound
Switching time	slow (milliseconds)	very fast
Wear	the contacts get old with use	no moving parts to wear
Works with	AC and DC locks	DC locks only
Flyback diode	most relay modules do not need one	must add one (1N4007 or 1N5819)
Isolation	yes	yes, with a PC817 optocoupler
Choose it for	a simple, common setup	a silent lock, or a door that opens many times a day

A solenoid lock is only locked or unlocked, so the MOSFET module does not give extra control here. Its gains are: no click, and nothing wears out. Both turn on when the pin is HIGH, so the code stays the same. Do not keep the lock unlocked for a long time, or it gets hot. This is the same with a relay.

A solenoid valve works the same way as a solenoid lock. To see how to wire and code one with both a relay and a MOSFET module, see the Arduino Mega - Water/Liquid Valve tutorial. The wiring for a solenoid lock is in the Arduino Mega - MOSFET Module tutorial.

Video Tutorial

Learn More

Arduino Mega - Electromagnetic Lock

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