Abstract: A protective circuit for removing power from a load detects the presence of a control signal which causes electrical power to be delivered to a load, for example, via a controlled switching device such as an electromechanical relay or a solid state relay. The protective circuit also detects the presence of voltage across the load, signifying that the controlled switching device is causing power to be supplied to the load. The protective circuit removes power form the load when there is an absence of control signal and there is voltage across the load, indicating a failure of the controlled switching device.

Abstract: An adjustable frequency oscillator has an adjustable element, such as a potentiometer, for setting the frequency of oscillation. The circuitry in the oscillator is such that the frequency of oscillation is relatively immune to the characteristics of the adjustable element. The oscillator may be used in a time delay circuit, notably, in a time delay circuit used to control a time delay relay.

Abstract: Apparatus for the activation of a remotely located device, such as a lamp or bell, under the control of telephone subscriber tip and ring lines. The apparatus of the present invention is located in the general vicinity of a called telephone subscriber station and is operated to activate and power a remotely located annunciator as a function of detecting ringing signals initiated by a calling telephone subscriber station. The apparatus plugs into a wall outlet for providing actuating power to the remote annunciator(s).