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 ...

This simple code lock circuit described here is of an electronic combination lock for daily use. It responds only to the roght sequence of four digits that are keyed in remotely. If a wrong key is ...

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 ...

The answer is actually quite simple, but let me first explain why that locking device is there. Section 422.30 of the National Electric Code (NEC) requires a disconnecting means for all appliances.