This electronic door lock has a remarkable conception because it uses only one active component.
How does it works ?
To put the relay in tension the 4 buttons S1 – S4 must be pressed. If anyone of the 4 butoons S5 – S8 are pushed the relay dont’s tension ( dont receives supply voltage ).
The supply voltage must be equal to the working voltage of the relay. One transistor like BD135 can commute up to 0.5A, in the same tine 2N2222 can do only 0.2A.


Enjoy this electronic door lock, its easy to build and straightforward.

Electronic door lock circuit diagram

electronic door lock schematic