Simple Electronic Combination Lock

The following diagram illustrates a straightforward electronic combination lock utilizing the IC LS7220. The component part list includes: C1 = 1µF 25V, C2 = 220µF 25V, R1 = 2.2K Ohm, Q1 = 2N3904 or 2N2222, D1 = 1N4148 or 1N4001-1N4007, and K1 = 12V SPDT Relay or any appropriate alternative.

The electronic combination lock circuit primarily operates based on the LS7220 integrated circuit, which is designed for security applications requiring a coded input to unlock a mechanism. The LS7220 is a highly integrated device that provides the necessary logic to interpret the key sequence entered by the user.

The capacitor C1 (1µF, 25V) serves as a coupling capacitor, filtering out any noise from the power supply and ensuring stable operation of the IC. Capacitor C2 (220µF, 25V) acts as a decoupling capacitor, providing additional stability and energy storage for the circuit during operation.

Resistor R1 (2.2K Ohm) is used to limit the current flowing into the base of the transistor Q1 (either 2N3904 or 2N2222), which functions as a switch to control the relay K1. The choice of transistor allows for sufficient current amplification, enabling the relay to activate without overloading the IC.

Diode D1 (either 1N4148 or 1N4001-1N4007) is included to protect the circuit from back EMF generated when the relay coil is de-energized. This diode is connected in reverse bias across the relay coil terminals, ensuring that any voltage spike is safely redirected away from the sensitive components of the circuit.

The relay K1 (12V SPDT) serves as the actuating mechanism for the lock, allowing it to control a locking mechanism or other devices requiring a switchable action. The relay can be replaced with any appropriate alternative that meets the voltage and current specifications required by the application.

Overall, this combination lock circuit is designed for simplicity and effectiveness, making it suitable for various security applications where electronic access control is needed.The following diagram is a very easy and simple electronic combination lock based on IC LS7220. Component Part List: C1 = 1uF 25V C2 = 220uF 25V R1 = 2.2K Ohm Q1 = 2N3904 / 2N2222 D1 = 1N4148 / 1N4001-1N4007 K1 = 12V SPDT Relay / Any approp.. 🔗 External reference