Abstract: Methods, apparatus, and systems are provided for an access controlled parking system. The invention includes a parking access system with a public parking location having controlled access; a garage door opener transmitter adapted to generate at least one unique signal; a receiver operable to receive the unique signal from the garage door opener transmitter; a processor coupled to the receiver and operable to grant or deny access to the public parking location based on the unique signal and to communicate receipt of the unique signal from the garage door opener transmitter to a central system; and a database system within the central system operable to associate the unique signal with an account for payment for use of the parking location. Numerous additional aspects are disclosed.

Abstract: A two-wire, admittance-responsive instrument system in which a transmitter, receiver and calibrator are connected by a two-wire transmission line is disclosed. The calibrator repetitively transmits a calibration enabling signal causing the transmitter to increment a reference admittance for comparison to a sensed admittance corresponding to a known physical condition. The calibrator monitors the bistable output signals transmitted by the transmitter in the calibration mode, which changes state when the incremented reference admittance bears a predetermined relationship to the sensed admittance. The calibrator may then transmit additional calibration enabling signals causing preload to be established for transmitter operation.