Electronic Key Operated Security Door

Electronic Key Operated Security Door

Circuit Project Description

The simple circuit was designed to create a security option for entering a door that would require electronic key inputs.

Terminology 4066 – a digitally controlled quad  analog switch utilizing advanced silicon-gate CMOS technology with features such as individual switch controls, matched switch characteristics, pin and function compatibility, low quiescent current, low ON resistance, wide analog input voltage range, and 15 ns typical switch enable time4N25 – a general purpose optocoupler that consists of a gallium arsenide infrared emitting diode driving a silicon phototransistor in a 6-pin dual in-line package used in microprocessor inputs, digital logic inputs, and power supply regulators due to its features such as high isolation voltage between input and output, operating temperature up to +110ºC, and available in wide-lead spacingBC550 – an NPN general purpose transistor with low current and low voltage used for low noise stages in audio frequency equipment Circuit Explanation

There is a handful components used in this circuit which makes the construction simple. The optocoupler IC2 can only be activated by entering the right combination of keys with the right line. An optocoupler is a component made of solid state that utilizes light emitting diode to transfer light via a barrier that is optically transparent. It provides circuit insulation by not allowing current to pass, except light. The door lock will be trapped in the case of wrong combination of keys. This trapped mechanism can only be unlocked by pressing the push button switch S1 or S12. Switch S1 is the external restoring process while switch S12 is done internally.

The initially set code of the circuit was 147, which can be modified very easily. This can be done by changing the connections of the keyboard switches. A additional exterior circuit like relay, can be driven by the optocoupler IC2. doing this will make sure electric isolation is done simultaneously between the two circuits. Since the circuit is simply constructed with few components, it can be supplied by a 9 V battery source.

Part List

R6 =10Kohm
R9 =47Kohm
IC1 = 4066
IC2 =4N25
S1…11=Push button sw or keyboard
S12=Push button normal closed
All resistors is 1/4W 5%


The electronic key operated door is merely found in places where unauthorized entry is prohibited. It works by verifying the person passing through the door to provide access keys to gain entry. They are widely used in banks, factories, restricted offices, prisons, jewelry shops, hotels, homes, apartments, and other establishments. It can be integrated with other security accessories and electric devices like external bells or magnetic contacts, depending on the required security conditions. This circuit can also be applied in controlling the locking and unlocking of vehicle doors.  But most importantly, it is an added security feature that is easy to build.

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