Touch Operated Code Lock Switch Circuit

This touch operated electronic door lock can be used for locking any entrance through a touch keypad. The lock's touch feature is foolproof and impossible to crack since the touch function is required to be on 3 programmed pads together or simultaneously, otherwise the lock doesn't respond.

It is a lot convenient to open a door using a code lock as compared to carrying weighty metal keys with us. Aside from this, traditional keys can easily get misplaced, but this cannot happen with code locks.

Advantage of Touch Operated Code Lock

The circuit diagram below exhibits a code lock that enables it to be opened through an effective three-digit code. But, this specific lock performs this function in a somewhat unconventional and unique technique. In this system, 3 digits has to be touched concurrently, meaning three fingers must touch 3 designated code buttons simultaneously.

Any one finger touching the incorrect button would simply not allow the relay to actuate. As the diagram distinctly indicates, it is actually out of the question for an intruder to speculate from the lock's layout exactly how it can be decoded.

This particular characteristic, alongside the huge range of combination possibilities, causes it to be extremely hard for an onlooker to crack the lock code. Another advantage is, involving 3 fingers together helps to cover the keyboard and hides the code operation from an onlooker, and the person finds it extremely difficult to understand which 3 pads were tapped by the owner.

How it Works

In all 5 CMOS ICs are used here. All the gates from the IC 4050 are used as buffers whose inputs can be seen connected with the touch keypads.

These buffers ensure that the touch operation are effectively converted into logic output signals without any malfunction. Because our finger may have varying resistance levels and pressure causing the output to oscillate and generate fluctuating outputs. The buffers ensure this never happens regardless of the touch variation.

The only criterion being the code number which must be touch simultaneously without fail for the lock to open.

The output from the buffers are further wired with Hex Inverter IC 7404 and the processor ICs 7430, 7410 which finally execute the relay activation when the code is correctly tapped. An electronic door opener may be configured with the relay contacts for implementing the lock opening and closing operations.

The code for the shown circuit illustration is 9-11-4. Any time this program code pads are simultaneously tapped with fingers, the inputs of N2, N3 and N4 turn logic '0'; consequently, the three inputs of N8 and the output of N5 create a logic '1'. Assuming none of the other keypads are tapped except the coded ones, all inputs of gate N7 remain logic '1', which results in the relay to become activated and the LED to illuminate. The relay can be employed to operate an electric door opener mechanism for opening the lock.

About Swagatam

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials.
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