Abstract: A closed-loop control for sensing the completion of popcorn popping in a microwave oven and automatically shutting down the oven. A microphone type sensor is acoustically coupled to the microwave oven cavity and provides an electrical signal to an amplifier and filter. The amplified and filtered signal is processed by a pop detector which includes an integrator and shut-down command generator responsive to a decreasing rate of popping to shut the oven off. The integrator provides a pre-pop timer function to maintain the oven on until popping commences. In an alternative sensor embodiment, a piezolelectric type sensor is used. In an alternative pop detector embodiment an adaptive threshold comparator which automatically adjusts pop detector operation to discriminate the popping signal from ambient noise present in the oven.

Abstract: An acoustic sensor assembly for a microwave oven of the type having an oven cavity defined by walls. The acoustic sensor assembly comprises an acoustic sensor for converting sound into an electrical signal representative thereof, and aperture in the wall of the microwave oven cavity of sufficiently small to prevent microwaves from passing therethrough. The assembly further includes a hollow conduit, for example a plastic tube, having first and second ends and secured to the aperture at the first end and to the sensor at the second end for acoustically coupling the sensor to the aperture such that sounds in the cavity are passed through the aperture to the sensor.

Abstract: A combined transformer and motor is disclosed having a continuously energized primary winding producing a continuous output voltage from a transformer winding and a selectively enabled motor shaft rotational output which is selectively actuated by powering a further winding, along with compensation means to stabilize the continuous output voltage in view of the selective actuation of the further winding.

Abstract: A combined transformer and motor having a continuously energized primary winding producing a continuous output voltage from a transformer winding and a selectively enabled motor shaft rotational output which is selectively actuated by powering a further primary winding, and further having at least one shading band for improving the regulation of the output voltage.

Abstract: A combined transformer and motor having a continuously energized primary winding producing a continuous output voltage from a transformer winding and a selectively enabled motor shaft rotational output which is selectively actuated by powering a further primary winding, and further having a reduced cross section area in the flux conducting structure of the combined transformer and motor for improving the regulation of the output voltage.