Remote controlled garage door opening system

DETAILED DESCRIPTION In accordance with a key feature of the present invention, a form of code hopping embodying a unique sequential decryption/comparison technique is incorporated into the operation of a remote control system for activating barrier opening apparatus, particularly garage door or gate openers.
In addition, the remote control system is of a "learn" type, but one in which the authorized operating codes stored in the receiver during the learn mode are never themselves transmitted from the transmitter.
Broadly stated, the remote control system of the present invention comprises one or more RF transmitters and a digital type RF receiver associated with the door operator.
The receiver is initially programmed with a "manufacturer's key" value.
Every system produced by a given manufacturer has the same manufacturer's key.
In addition, each transmitter is initially programmed with a unique serial number and unique "secret key".
The secret key stored in the transmitter is generated using the unique serial number of the transmitter and the manufacturer's key.
Thus, every transmitter has a different serial number and a different secret key.
When the transmitter is activated, it performs a nonlinear encoding function using the secret key to generate a changeable hopping code signal.
The hopping code changes (i.
e.
, hops) every time the transmitter is activated.
The transmitter's unique secret key is never transmitted, and although the transmitter's unique serial number is transmitted, it is not stored in the receiver.
In accordance with a feature of the invention, the secret key value which is stored in the receiver is self-generated in response to the encoded transmission from the transmitter during the program or learn mode of the receiver.
During the subsequent operate mode, the receiver then uses the previously generated and stored secret key to decode the hopping code signal from the transmitter.
The door operator or opener device is activated when such decoded information is within a "window" or range of acceptable values as determined by a sequential comparison technique subsequently described