Fail safe system for a mechanical lock and key set with electrical interlock

Claim 1

A fail safe circuit adapted for preventing the deciphering of a coded electronic interlock for a mechanical lock, the lock having a rotatable cylinder and a mated key applicable in a normal mode for unlocking a system when the mated key is inserted in the cylinder and the key and cylinder are rotated from a locked position to an unlocked position, the interlock precluding enabling of the system until a preselected activation signal is generated in response to the rotation of the key and cylinder, the interlock including a sensor for determining the rotation of the cylinder and the key, and a signal generator having a preselected activation code controlled by the sensor for generating a system activation signal in response to the rotation of the cylinder and key, the fail safe circuit being in communication with said signal generator, said fail safe circuit adapted for preventing the unauthorized reading of the value of the preselected code when a mated key is not present in the cylinder of the mechanical lock, the fail safe circuit comprising: a. a transistor switch circuit in communication with the signal generator and operable when the key is not present in the cylinder; and b. an amplifier circuit for receiving said activation signal when said transistor switch is operable, the amplifier circuit adapted for isolating the signal generator from the circuit and providing a false signal when an attempt is made to read the coded activation signal of the generator without inserting a mated key in the cylinder and rotating the key and cylinder.