Electronic Number Lock System Using SCR

A vital part of any home, flat or workplace is a lock. After shutting up his house, a man can leave without trouble. Stealing is a possibility otherwise. Currently, mechanical locks that have levers and require a key to a open door. Every lock has a unique key. However, rust can harm these locks as they age. Thus, the owner needs to purchase a new one.

These days, the market has seen the development of electronic number locks that are simply controlled by passwords. We are going to construct an electronic number lock system as part of this project. Here, we explain the operation of an electronic number lock using switches and a relay. You may connect locker locks, door motors, and any kind of electronic lock in the load position.

Principle Behind Electronic Number Lock System

This article refers to the electronic number lock as an electronic device that works with a mechanical number lock. To run the relay attached to the load, three predetermined numbers are turned on one at a time. The load that is connected to the relay receives power and begins to function once the code has been input.

Circuit Schematic

Electronic number lock system using scr


EC103D SCR (x3)
1KΩ Resistor (x3)
10KΩ Resistor
4.7KΩ Resistor
BC148 Transistor
SL100 Transistor
12V Relay
Push Switch (x11)
12V Power Supply

Block Diagram of Electronic Number Lock System

Block diagram of electronic number lock system

Working Principle of Electronic Number Lock System

The fact that this project uses so few components contributes to the simplicity of the operating principle. Here, SCR is used in three switching circuits. One can turn on each switch in turn. The push buttons on each switching circuit are referred to as the “number.” The “wrong use of the system’s circuit” is connected to the other switches. As indicated by the circuit diagram, any three of them may be chosen.

The circuit can be turned on by entering the three switches correctly; if not, it stays off. The system can turn off under two different circumstances. First, the SCR is turned off by cutting the positive voltage. Second, the SCR stays off when the gate has a strong negative current.

Three SCRs are connected in series in this circuit. A 1KΩ resistance connects the SCRs’ anode and cathode to the negative. SCR1 and SCR2, in turn, are loaded by this resistance. A relatively little amount of electricity can flow through these resistors.

SCR3 is linked in series with a 10KΩ resistor to the base of the BC148 transistor. The base and collector of the SL100 PNP transistor are connected to the emitter and collector of the BC148 transistor, respectively. The positive and collector terminals of the SL100 are linked to the 12-volt relay. The ground is linked to the SL100 emitter.

The gate terminals of SCR1, SCR2, and SCR3 are connected to three switches, S1, S2, and S3, respectively. The other switches are connected with 100Ω resistance between the negative terminal and the gate of the SCR. Pressing S1 causes the SCR1 gate terminal to receive a positive voltage via resistor R1, activating the device. SCR2 turns on when S2 is pressed because the SCR1 cathode provides the positive voltage needed for SCR2’s gate to open.

Finally, when S3 is turned on, a positive voltage is applied to the gate terminal of SCR3, turning SCR3 on. SCR3’s cathode is linked to T1’s base, which receives a positive voltage. As a result, T1 and T2 are also activated simultaneously. When T2 activates R1, the relay conducts.

What will happen if the incorrect switch is pressed in the condition at this point? More negative current flows from R2 to SCR1 in the event that the incorrect switch is pressed. SCR1 then switched off. Moreover, the SCR2 and SCR3 were disabled due to their zero anode voltage.

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