The Electronic Digital Combination Lock SAFE Kit With Variable Resistor Dial

Introduction: The Electronic Digital Combination Lock SAFE Kit With Variable Resistor Dial

About: Hi there! My name is Patrick, and I am an electronics engineering technician who works full time as a lab tech, and part time as an electronics engineer/salesman. I own an ebay store, and two websites, which …

Hi all!
Thanks for looking at my instructable.  This instructable is for an electronic "safe" circuit that I developed into a kit.  It allows for the user to program a four digit code using an external variable resistor dial on power up.  Depending on which way you turn the "dial", the on-board seven segment display will output a number between 0 and 9.  I implemented a 10-turn variable resistor as a dial to emulate a safe dial.    Only that four digit code will disarm  the device and turn on a relay that can control AC devices.  I will be using this device with a solenoid and a door lock so that the lock only opens when the correct code is entered.  The relay controls the solenoid, which opens and closes the door locking mechanism.  At the end of the video, I show you how to control AC devices using this device.  I had the idea for this kit about three months ago, and I ended up taking the steps to have a printed circuit board built up for it.  If you like this instructable and design, please vote for me in the Mad Scientist Contest =)

1) Code entry timeout:  If the user takes too long to enter in a code, there is a timeout sequence that starts the code entry time over again.  If the timeout occurs, there is an indicator (Seen in the video).  At which point, the user must start over again in entering the code.
2) AC/DC device control using an on board relay - The relay only activates when the proper code is entered.
3) Alarm sequence: If the user enters in the incorrect code, an on board buzzer is enabled, and acts as alarm.

The video features:
1) Schematic review
2) Assembly instructions (Of available kit)
3) A demonstration of the functionality
4) A demonstration (At the end of the video) of how to control AC devices

Here are the schematic and code files:
Schematic Diagram:

f you're interested, a kit is for sale at and can also be found on our ebay store here:

Thanks for watching.  I hope you like it!  I had a lot of fun designing it!

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