An Electronic Combination Lock Circuit Using the LS7222 IC As a Platform

Introduction: An Electronic Combination Lock Circuit Using the LS7222 IC As a Platform

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 everyone!
Thanks for having a look at my instructable.  As of recently, I've been working on several combination lock circuits.  Most of these circuits will be added to instructables after Christmas.  THIS instructable is for a combination lock circuit that I created using the LS7222 user-programmable combination lock IC as a platform.  The user can program three codes (ARM/DISARM/DURESS) by typing in a special sequence into the keypad.  The 12-digit keypad allows for you to program 38416 different combinations.  You can also add in up to 16 buttons to make it even more impossible to crack your combination.  When powered on, there are default codes for the ARM, DISARM, and DURESS codes.  However, you can easily reprogram them by following along with the video.  

About the circuit:
There are 5 outputs that all display different logic based on which code is entered.  These outputs are (ARM/DISARM/LOCK/TAMPER/ALARM)   If an incorrect character is typed in, the TAMPER output goes high for a short period.  There is a capacitor on board that can be interchanged to lengthen or shorten the pulses on  outputs such as TAMPER, ARM and DISARM.  There is another capacitor on the board that can be interchanged to lengthen or shorten the code entry time.  These capacitors are talked about in the video.

This project can easily be interfaced with a relay board (Connected to the LOCK output) so that you can turn on an AC device, or control an external device when the DISARM code is entered.  There is a regulated 5v VCC pin and GROUND pin so that you can easily interface this project with other circuits.

The video shows you:
1) How to build the circuit (assembly instructions).
2) A schematic review.
3) How to program the three codes (Programming sequence).
4) How to interface with an external circuit or MCU.   
5) How the outputs change based on which code is entered.

Where to find the parts:
This circuit requires mostly passive components, and you can find the LS7222 IC on ebay.  We sell the kits here:  Or at under "entry Level Kits".

The DATA SHEET for the LS7222 IC is here:

I hope that you've enjoyed this video instructable.  I really enjoy making step-by-step instructables more than video, but I'm sure that you'll find that the video is EXTREMELY DETAILED!  Please let me know if you have any questions at all!

Thanks for watching everyone! 

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    9 years ago on Introduction

    Is there any way to do this and keep it only DC to avoid the dangers of AC? Is there also a way to connect a buzzer up to it (and have it go off if the incorrect passcode is entered in?)


    9 years ago on Introduction

    Hi! Quick question; is there a way to stop this defaulting to the factory codes when power is interrupted?