Switching apparatus for closed circuit television monitoring systems

Abstract

A solid state switch assembly for selectively coupling a TV monitor to one of a plurality of TV cameras. A random access memory is utilized to establish the switching sequence. The switch is advanced through the desired sequence by activating an oscillator to step a counter. The counter output addresses each memory location and the state of the addressed memory location controls either a termination or a continuation of the switching sequence. The counter output also sets an analog type switch for selecting one of the plurality of video inputs to be coupled to one or more of the video monitors. The system is capable of displaying the selected video input signal on a plurality of monitors through the use of impedance matched current amplifiers. A biasing circuit is provided to allow the switch to handle signals making positive signal excursions above the system ground without interference with the positive voltage supply. Switching circuitry is provided at each monitor position for application of a negative holding signal to a hold sensing circuit through the coaxial cable connection between the camera and the monitor to thereby deenergize the aforesaid oscillator. Impedances are provided to prevent the video signals from being shorted out as a result of operation of the local hold buttons for the monitors so as not to degrade the scene being displayed.

Dependencies are inferred from the claim text.