DTMF Code Lock

Whether simple or ‘uncrackable’, whether constructed from discrete logic or using a microcontroller — code locks have become something of a tradition in Elektor Electronics. This one, however, is different!This special code lock has no keyboard, but instead responds to DTMF tones, as produced by any modern mobile phone or, of course, a pocket DTMF generator. Since noone who is anyone leaves their house these days without their mobile phone (although they might forget their front door key), almost anyone will be able to use this device. The lock presents to the outside only a microphone capsule and four LEDs, which show the status of the unit. Their function will not be obvious to the uninitiated. The electronics consists mainly of standard components and contains no programmable devices at all.