Electronically controlled door lock - includes key card having combination of resistors whose values are measured by lock circuit

摘要

The electronic lock includes a card having a set of 8 male contacts, and a base having a corresponding number of socket terminals. The card constitutes the key, while the base forms the lock. When the card is introduced into the base, the base circuit measures the value of the four resistance in the card. If these are correct, then the lock permits the changeover of a monostable electric relay switch. The resistors are chosen from 35 different values spaced by 3 % of their maximum value, with a tolerance of 1 % Four resistors chosen from this range give in excess of a million possible combinations. ADVANTAGE - Does not rely on a code number which may be divulged, or on magnetic card requiring expensive reader.