Lock Machines with Passwords

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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.

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.

  • Lock Machines with Passwords


Step 3: Hardware – Connecting the circuit

Lock Machines with Passwords
Lock Machines with Passwords

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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.

  • Lock Machines with Passwords


Step 5: Assembly

Lock Machines with Passwords

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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.

arduino – Lock Machines with Passwords, in category: technology