Methods and apparatus are provided for supporting a variable-length transport packet in a audio and video communication system. The invention is characterized in that at least one or more adjusting rotational devices which are driven by an electric motor are provided on each side of the brake disk to adjust the axial distances between the brake pads and the brake disk. The pair of interconnect pads are formed on a first surface plane of a first layer of the substrate. To facilitate the vertically oriented fractions of the electromagnetic field, there is at least one emitter which extends vertically at the circumference of the loop emitter and to the conductive base surface and which is electromagnetically coupled to both the loop emitter and the electrically conductive base surface. The switching or superimposition is then always carried out between microphone signals with the same signal level, so that the switching or superimposition does not result in any sudden level changes. The DCDC converter includes a DCDC converter part converting an input power into a predetermined DC power by switching the input power to thereby supply the converted DC power to a light emitting device; and a control part controlling switching of the DCDC converter part in accordance with a driving signal applied to the light emitting device to thereby control a voltage level of the DC power.