This article introduces an electronic code door lock system featuring a transistor-based code lock circuit. Previously, we demonstrated how to construct a password-based door lock system using an 8051 microcontroller, which necessitated programming. However, the notable aspect of this circuit is that it can be implemented without any programming. It comprises only a transistor and a few buttons.
Outline
- One Transistor Electronic Code Lock System Circuit Principle:
- One Transistor Electronic Code Lock System Circuit Diagram:
- Simple Transistor Code Lock Circuit Simulation Video:
- One Transistor Electronic Code Lock System Circuit Design:
- Simple Transistor Electronic Lock System Project Output Video:
- How One Transistor Electronic Lock System Circuit Works?
- Electronic Code Lock System Circuit Advantages and Applications:
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- Limitations of this Circuit:
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One Transistor Electronic Code Lock System Circuit Principle:
The fundamental principle of this circuit is that the door lock will exclusively unlock when all of the buttons in series are simultaneously pressed. If any button in parallel is pressed, the door remains locked. When all these buttons are pressed concurrently, the transistor triggers the relay, subsequently unlocking the door. Arranging these buttons in a specific sequence allows for real-time door unlocking.
One Transistor Electronic Code Lock System Circuit Diagram:
Circuit Components:
- Transformer.
- Bridge rectifier.
- Resistor.
- Capacitor.
- Buttons.
- Diode.
- Transistor.
- Relay.
- Motor
- Ac source.
Simple Transistor Code Lock Circuit Simulation Video:
One Transistor Electronic Code Lock System Circuit Design:
The circuit comprises a stepdown transformer with a 230V and 50Hz AC input supply. The primary coil of the stepdown transformer has fewer windings than the secondary coil.
Connected to it is a bridge rectifier, which rectifies the transformer’s full wave. The bridge rectifier has four pins, two of which are connected to the transformer. The resistor and capacitor are attached to the other two pins, one of which is grounded, and the other is linked to the resistor and capacitor. The opposite terminal of the capacitor is also grounded.
Four buttons, namely S1, S2, S3, and S4, are connected in a series with the resistor. They are then connected in parallel with another button, S5. A 100k resistor is connected in parallel with the buttons. The base of the transistor is also connected in parallel to these buttons. The emitter pin of the transistor is grounded. A 1N4007 diode is connected to the relay’s collector pin. The other end of the diode is connected to one terminal of the relay. This diode serves to protect the transistor from back electromotive force generated by the relay.
The relay has five pins, and one of them is connected to the diode’s positive terminal. Another pin is grounded. Consequently, the relay’s output is linked to the motor through the AC source.
This application uses a magnetic relay, and it has multiple pins, including NC (Normally Closed), NO (Normally Open), COM (Common), A, and B. When no voltage is applied to pins A and B of the relay coil, the COM pin is connected to the NC pin (Normally Closed). Conversely, when a DC voltage is applied to pins A and B of the relay, the COM pin connects to the NO pin (Normally Open).
Simple Transistor Electronic Code Lock System Project Output Video:
How One Transistor Electronic Code Lock System Circuit Works?
- Apply a 230V and 50 HZ input voltage to the transformer at first.
- As a result, the voltage is reduced to 6V by using a step down transformer.
- The bridge rectifier receives this lower AC voltage. This generates a pulsing DC signal.
- The output voltage is delivered to the buttons through a 2.2K ohm resistor.
- Now hit switch S1 first, then switch S3 to complete the process.
- Now push the S2 and S4 switches.
- As the parallel buttons are opened, current travels via these switches to the transistor base.
- The relay begins to switch, and the motor is connected to the supply.
- The motor is now spinning, indicating that the door lock is open.
Electronic Code Lock System Circuit Advantages and Applications:
- This circuit is very simple, reliable and low cost.
- We can use it in security applications.
- We can also use it in door lock systems to open the door.
Limitations of this Circuit:
- If the user forgets the password i.e. the order of the buttons to be pressed it is difficult to open the lock.
