Abstract: A secure communication link is provided for transmitting signals between a host computer and at least one authorized terminal. The communication link includes a host modem for modulating and demodulating the signals transmitted between the host computer and the authorized terminal and an access controller. The access controller stores enquiry and reply sequences of bits and is operable to compare incoming signals from the host modem with the stored sequences of bits. Where there is agreement between the signals from the host modem and the stored sequences of bits, the controller establishes the communication link. Where there is no agreement or no reply from the host modem, the controller disconnects the host modem from the link.

Abstract: A warning device (10), typically situated in an illuminated exit warning sign, broadcasts voice commands generated by a synthetic speech synthesizer (U3) via speaker (SP1). A programmable microcomputer (U2) senses a loss of AC power and generates a user initiated voice command. Upon the detection of a fire or smoke condition, the microcomputer (U2) generates a priority warning. The device (10) includes a self-contained, charged power supply (12) that powers the microcomputer (U2) and the synthesizer (U3) in the event that the externally supplied AC power ceases. Constant illumination is provided by lamps (32) or (40). A user operated switch aids in programming the microcomputer to provide two sets of audible phrases.

Abstract: A method and apparatus for controlling a resonant power module comprising a resonant power circuit which is coupled to a load. First and second switching elements are coupled to the resonant circuit for alternately supplying a flow of current. Trigger generator means are provided for supplying trigger signals to alternately enable the first and second switching elements. A control means is coupled to the trigger generator for operating the power module in a first mode in which the resonant circuit current is controlled by varying the repetition rate of the trigger signals. The control means operates the power module in a second mode by maintaining the trigger signal repetition rate at a fixed limit and controlling the resonant circuit current by varying the on/off duty cycle of the power module.