TRANSISTOR BASED ELECTRONIC DOOR LOCK

HELLO AND WELCOME BACK!!

During this pandemic era due to Recession and economic crisis home security is must as there are increase cases of theft ll around the world .

So in today's article I will tell you how I created (basically designed it from scratch) this transistor based electronic door lock which id very cost effective as well as cheap and its use can be very versatile from homes to offices .

LEt's start with build!!!!!!!!!

Basic Electronics components :
Transistors

capacitors

resistors

breadboard

perfboard

jumper wires

single core wires

batteries

hex keypad (or 16 switches)

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"GO ELECTRONICS"

To start with with we will need around seven transistors to make a three digit locking system , if you want to make a four digit locking system go with two more transistors it's your choice ..

Firstly we will divide the circuit into 3 sections

Now Let's understand the first section :

if we push the the switch by turning it ON the base of transistor Q1 and Q2 turns ON and charges the capacitor (C1) to the supply voltage

And when we turn the switch OFF the capacitor discharges via a discharging resistor R1 of 120K ohm by supplying enough voltage to base of Q1 and Q2 to maintain in its ON state until the capacitor entirely discharges .

So the idea behind this circuit is that if the door opens it will take some time to close And that time can be determined by the discharging process of capacitor via a discharging resistor.

The main advantage in this circuit is that we can adjust the closing time of door by changing the value of discharging resistor value .

To do a little experiment with the discharging values or the door closing time .

Now if put a discharging resistor value of 100K the time period until which the base if transistor remains ON is around 8-10 seconds as you can see the timer. This is because the discharging resistor value is quite high so the discharging process takes around 10 sec.

Now if we put a 10K ohm resistor the capacitor almost immediately discharges within less than a minute as you can see the timer .

Finally if we put a 220K resistor the time period of holding rises to about 20 seconds which is quite cool

so all in all our circuit works perfectly!!!!!

Instead of switches we will use a hex key board which is perfectly suited for this for this build as now it becomes more secure because the door opener now has to select from 16 membrane switches instead of 4 switches .

To Understand how I connected the switches in hex keyboard :\

initially the hex keyboard has 16keys or 16 membrane switches with 4 rows and 4 columns .Each switch has a common row and different column and vice versa .

if you want to select the first digit of your password code as 3 . So you have to connect one wire to pin 8 or orange pin which acts as a row and the other wire to pin 2 which acts as column .

For more detailed explanation watch the video!!!!

And now to understand the second and the third sections .They are basically the replica of the first section but one thing they can be operated only when the first section is ON or the first passkey is correct as the Emitter of first section is connected as a supply for next sections ...

Not to reveal the password but anyways I will change it later better don't try to break the my door lock . ok so you can see that the password is 51C.

When you type any other password the door won't open as it has three layers of security .

Final touch add a solenoid lock before final installation .

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