DIGITAL LOCK

Digital locks have many advantages over their conventional mechanical counterparts and perhaps the greatest is that no keys are required. Over the years many circuits for digital locks have been designed, usually based on special custom integrated circuits or even microprocessors with many features, such as built-in alarms to detect multiple incorrect entries by someone trying to break the code. It is possible, though, to construct a simple yet effective combination lock based on a single easily available counter integrated circuit. The design can be further simplified by defining the combination by means of wire links instead of storing it in a memorydevice. Whilst this makes it more difficult to change the code, it is unlikely that this will be problem. A coded lock circuit can also find many applications apart from the obvious one of its use in a door. By using the circuit to control a relay, the circuit could be used to switch on the supply to a piece of equipment, for instance, thus preventing its unauthorised use.