Combination lock with comparator - receiving signal patterns stored in memory and entered via external keyboard

摘要

The combination lock has a keyboard for entering signal patterns. A memory stores reference patterns and, unlike the keyboard, is not accessible from outside the device. A comparator compares both patterns and unlocks the lock if they are identical. The user can enter a new reference pattern into the memory via the keyboard when he has unlocked the lock and when a switch inside the device has been switched to 'insert new pattern'. A delay switch delays the unlocking of the lock after the two patterns have been found identical. A decoupling circuit decouples the externally-accessible keyboard from the externally-inaccessible circuitry which includes memory, comparator, switch, unlocking devices etc.