The main principle of this circuit is that the door lock opens only when the buttons in series are pressed at a time. We can use it to lock the doors and for other security purposes. This article ...

A very simple but highly efficient combination lock circuit is shown in the figure. Any type of on/off switches can be used, varying from commercially available inexpensive types to more sophisticated ...

Here is the circuit diagram of Electronic code lock system using 8051 microcontroller. It is very useful at residential places to ensure better safety. This system demonstrates a circuit named ...