Abstract: A feed-back noise-eliminating microphone circuit is provided. The circuit includes a positive-phase pick-up circuit to pick up sound source signal for amplification through a positive-phase amplifier for further output through a balance adjusting circuit and a power amplifier. The circuit further includes a reverse-phase pick-up circuit to pick up feedback signals from the loudspeaker for amplification through a reverse-phase amplifier, wherein feedback noise from the reverse-phase amplifier is offset at said balance adjusting circuit by the output signal from the positive-phase amplifier.

Abstract: A keyboard housing includes a key plate with a plurality of actuator keys mounted on an upper face and a waterproof chamber mounted on a lower face thereof and a device to retain the actuator keys in a normally unpressed position. A circuit board is disposed in the waterproof chamber. A switch contact assembly mounted on the lower face of the key plate which includes a first membrane having a first conductive pattern, a second membrane having a second conductive pattern and a partition membrane disposed between the first and second membranes to separate the first conductive pattern from the second conductive pattern in a normal open switch. The partition membrane includes a hole device which permits a portion of the first conductive pattern to engage with a portion of the second conductive pattern when the first membrane is pressed by one of the actuator keys, thereby generating a signal corresponding to the pressing key.

Abstract: This invention relates to a type of "multi-purpose traffic director's stick", featuring the composition of a bar tube, flashlight handle, lamp element, speaker and control circuit board, to achieve multiple purposes with a single director's stick without sophisticated equipment but the functions provided by a director's stick, police club, trouble alarm lamp, flashlight and a whistle.