Electronic Machine Locker

This device allows you to switch on electrical machines for a specific time. It helps monitor activity of scheduled machines. If the user enters the correct password, he/she will be able to use the machine connected to this device for two hours (time can be modified).

The idea of this project was inspired from a collection of instructables.

Thanks to the willygroup's blog for their password checking method.

This project was developed in FABLAB Dhahran.

Teacher Notes

Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.

Step 1: Requirements


  • Keypad 4*4
  • LCD 1602 (16 * 2)
  • Arduino Uno
  • Wires
  • 4 x M4 40 mm Screws and nuts
  • 5V DC Relay - 10 A 250 VAC - 10 A 30 VDC

Machines used:

  • Laser Cutter

Step 2: Making the 2D Design

Come up with your own design if you want to make the device have a different look and feel. The design that is proposed in this instructable is the default and has been used and is reliable. The design uses 6 mm acrylic, it consists of 6 layers, they are placed in order from left to right in the pdf file attached. The circuit should be mounted on the main (left most) layer. The layers will be screwed to each other using the M4 40 mm screws and nuts on the corners of the box.

Step 3: Hardware - Connecting the Circuit

The Arduino is connected to the LCD screen to display permission status and Time elapsed and warnings. The relay will be connected to the main power supply cable and will be the switch which will be controlled when the password is correct. The LCD and the relay will be powered up from the Arduino as shown in the circuit. The relay's control signal is connected to pin #13 on the Arduino. Five volts and Ground are also connected to the LED + and LED -, respectively, if the backlight of the LCD screen is needed.

The keypad will be connected to the Arduino according to the pin assignment in the table attached. You will have three wires connected to the relay from the Arduino's side. Now you will need to connect a power cable extension to the relay, make sure to connect the live wire (positive) to the NO (Normally Open) pin of the relay.

Step 4: Programming the Arduino

You will need to download the Time.h library before uploading the code to the Arduino. The password used is a 4-digit password "1010", it can be changed from the code in the following line:

char password[5] = "1010";

The time library will help keep track of time since the Arduino has been powered up. It will count two hours if password has been entered correctly, the relay will close the circuit for the upcoming two hours until the time is up. Warning messages will be displayed during the progress.

Step 5: Assembly

After screwing the parts together, the final shape should look similar to the one in the photo. You can you double sided tape to keep the keypad fixed on the 1 mm engraved top (right most) layer. If your LCD screen is too lose for the dimensions in this design, you can use a glue gun to stick it firmly on the top layer as shown. This project can have many different applications, its main purpose is to monitor and organize timings of electrical machines. In Fablabs around the world, this can be used on the laser cutting machines and 3D printers to monitor scheduled jobs on these machines.

Step 6:

1 Person Made This Project!


  • Made with Math Contest

    Made with Math Contest
  • Multi-Discipline Contest

    Multi-Discipline Contest
  • Robotics Contest

    Robotics Contest

9 Discussions


1 year ago

hi there

can you upload enclosore box dimensoin or cad file please ?

and video?


3 years ago

Hey I'm experiencing some errors in the code? would i be able to get some help with this please? i have never used arduino before and having trouble correcting it


3 years ago

Hey there! Luke here, i was wondering if you could do me a huge favour and take a picture of the inside of the device? that would be so helpful :)


3 years ago

Also, Can you list as many machines that this can be connected to as possible? I would really appreciate it :)


3 years ago

Hi there,

Luke here again. I was just wondering if you could let me know the dimensions of the frame for the CAD design so I can get it cut out? As much dimensions as possible is helpful. As the PDF can not be opened using the CAD programme.

Many thanks,



4 years ago

Excellent, thank you! So the connections within the device, does it involve soldering? And how long did it take you to make this project? Thank you for your time and help with this, I really appreciate it :)

1 reply
FABLAB DhahranLukeD17

Reply 4 years ago

You're welcome. The connections with the relays and the arduino were not soldered. But the wires connected to the LCD were soldered. The project was done in FABLAB Dhahran over a period of 3 days (6 - 9 hours working time).

If you have any other questions please let us know :)

Good luck.


4 years ago on Introduction

Hi there, was wondering if you could answer some questions for me?

What connection do you have on the end of the black cable? are there two cables leading from the device? how does the device connect to the machine?

I will be making this for my college project so all information you can give me will be much appreciated. :)

1 reply
FABLAB DhahranLukeD17

Reply 4 years ago on Introduction

Hey Luke,

The black cable is a simple power cord extender like the one in the picture below. This cable is not connected to anything other than the relay inside the box, the power cable was stripped, and only the live (red) wire was cut and connected through the relay. The power cord is connected to any power plug and the other extended part is where the machine you want to control is connected. It's always better if you use a long cable.

If you have any other questions about the project then feel free to ask :)