A lock is a very essential part of any house or apartment or office. A man can go away from his house peacefully after locking the house. Otherwise, there is a chance of stealing. At this time mechanical locks are used which have levers and can be unlocked by key. Each lock has a different key. But after getting old, these locks can be damaged by rust. So the owner has to buy another one.
Nowadays there is an electronic number lock introduced in the market which can be easily operated by passwords. In this project, we are going to build an electronic number lock system. We show here how an electronic number lock works with a relay and switches. In the place of load, you can connect door motor, locker locks, and any type of electric locks.
Principle Behind Electronic Number Lock System
The electronic number lock is described here as an electronic unit operated with a mechanical number lock. Three selected numbers are operated one by one so the relay connected to the load can be operated. When the code has been entered, the load connected to the relay gets the power and starts working.
- EC103D SCR (x3)
- 1KΩ Resistor (x3)
- 10KΩ Resistor
- 4.7KΩ Resistor
- BC148 Transistor
- SL100 Transistor
- 12V Relay
- Push Switch (x11)
- 12V Power Supply
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Block Diagram of Electronic Number Lock System
Working Principle of Electronic Number Lock System
The working principle is so simple because there are very few components are used in this project. Here three switching circuits are used with SCR. Each switch can be ON one after another. Each switching circuit consists of push buttons called the ‘number’. The other switches are connected to the ‘wrong use of the system’s circuit. Any three of them can be selected as shown in the circuit diagram.
By entering the correct three switches the circuit will turn on, otherwise, the circuit remains turn off. There are two conditions to make the system turns off. Firstly, when the positive voltage is switched off, the SCR is turned off. Secondly, when the gate has a high negative current the SCR remains turned off.
In this circuit, three SCRs are connected in series. The anode and cathode of the SCRs are connected to the negative by 1KΩ resistance. This resistance works as a load for SCR1 and SCR2 respectively. By these resistors, a very small amount of current can pass.
SCR3 is connected to the base of the BC148 transistor in series with 10KΩ resistance. The collector and emitter of the BC148 transistor are connected to the collector and base of the SL100 PNP transistor respectively. The 12-volt relay is connected between the positive and collector terminal of SL100. The emitter of SL100 is connected to the ground.
Three switches S1, S2 and S3 are connected to the gate terminal of SCR1, SCR2 and SCR3 respectively. The other switches are connected between the SCR’s gate and negative terminal with 100Ω resistance. When S1 is pressed, the SCR1 gate terminal gets the positive voltage through resistor R1 and turns on. When S2 is pressed, the SCR2‘s gate gets the positive voltage through the SCR1 cathode and then SCR2 turns on.
At last, when S3 is on, the SCR3‘s gate terminal gets positive voltage and SCR3 turns on. The cathode of SCR3 is connected to the base of T1 which gets positive voltage. So T1 and T2 are also turned on at the same time. The T2 activate R1 and the relay starts to conduct.
Now the condition is what will happen if the wrong switch is pressed. If any wrong switch is pressed the SCR1 gets more negative current through R2. So SCR1 turned off. The SCR2 and SCR3 were also turned off because their anode voltage are zero.