Television shut-off device

Claim 1

A television shut-off device comprising; a television set for receiving and transforming a plurality of electromagnetic signals to corresponding television channel video and audio signals and having an AGC circuit and a bias supply therein, an AC power supply for supplying power to the television set for reception and transformation of said channel signals, circuit means connecting the power supply to the television set and including switch means for opening and closing the circuit means to control energization of the television set from the power supply, detector circuit means connected to the AGC circuit of the television set and bias supply in the television set and including electromagnet means connected to and operating the switch means in the circuit means for the opening and closing of the circuit means from the power supply to the television set, said detector circuit means including means for selectively detecting the presence of a signal indicative of the presence and absence of a video signal in the television set through comparison of a voltage in the AGC circuit and the bias supply, said signal detecting means including a two stage amplifying switching device responsive to the differential between the reference level signal and the AGC signal and in which one stage is energized with the presence of the video signal and the other stage is energized with the absence of a video signal in the television set, timer means included in the detector circuit means connected to and responsive to the means selectively detecting the presence of a signal indicative of the absence of a video signal and providing a pulsed output signal therefrom at the end of a predetermined period of time, said timer means including an RC network, a unijunction transistor, and an additional transistor, the RC network upon discharge controlling the firing of the unijunction transistor to provide the pulsed output signal to the switch means, said additional transistor being connected to said amplifying means and responsive to the signal indicative of the absence of video signal in the television set to become operative to control the discharge of the capacitive component of the RC network connected to the unijunction transistor to control firing the same, switching means having two conditions of operation connected to the timing means to be operated to one condition of operation with the pulsed output signal from the timing means, and means connecting the switching means to the electromagnetic means in the detector circuit for opening the circuit means connecting to the television set from the power supply under the presence of said one condition of operation of the switching means.