A light control circuit for a video camcorder, where said video camcorder includes an illumination light. The light control circuit includes a pause switch for enabling the light control circuit. A light on/off control is responsive to the pause switch and controls a light control relay. A record signal delay is responsive to the on/off control and applied a record signal to a microcomputer a predetermined elapsed time after operation of the light on/off control. An illuminance detector is responsive to illuminance surrounding the video camcorder and generates a comparison output signal indicative of the surrounding illuminance. A light control is responsive to the light control relay and controls the illumination light associated with said camcorder.

An address discrimination channel and terminal selection channels are established in the low-noise region of a first one of two succeeding cycles of an alternating current carrier wave, whereas returning channels are established in the low-noise region of the second cycle of the same. A receiver inserts an address discrimination phase-pulse signal and a terminal selection phase-pulse signal, respectively, into the address discrimination channel and the terminal selection channels of the aforementioned first cycle. A terminal equipment inserts a returning phase-pulse signal into the returning channels of the aforementioned second cycle when it detects the address discrimination phase-pulse signal on the address discrimination channel, and the terminal selection phase-pulse signal having an address code coinciding with the address code of said terminal equipment on the terminal selection channels.

A transformer, typically a miniature transformer, to provide low-voltage power between, usually, 2 to 12 V from a power network has an auxiliary winding (6) inductively coupled to the core (9) of the transformer. A reference signal is provided from the power supply, and a monitoring circuit (32), which includes a difference-forming circuit (16) is coupled to receive (a) a signal from the auxiliary winding (6) and (b) the reference signal, the difference-forming signal providing an output in dependence on the state of magnetization of the core, by evaluating differences in magnetization (.DELTA.B) depending on whether power is being supplied by the transformer, or not. A circuit interruption element (10), typically a transistor, is serially connected between the power supply (1, 2) and the transformer. To determine if, after disconnection, the load should require power, for example if the load is a user-operated appliance, or a rechargeable battery, periodically requiring recharging even if the battery is not in use, an interrogation circuit (30) is coupled to the power supply to periodically, or aperiodically, based on time, or on the value of a physical parameter, reconnect the transistor (10) for a brief interval, in the order of milliseconds, to permit determination if power is being required, or not. If power is required, the transistor will remain conductive; if no power is required, however, the circuit will again control the transistor to non-conduction, thereby saving magnetization current flowing into the transformer if there is no need, based on required power.

The coupling device comprises a transformer having a primary winding in series with a two-way switch controlled via an optocoupler and a three-position selector switch by a control circuit. In standby mode, the switch is connected to an oscillator defining a switching frequency (49 kHz) ensuring power supply of the control circuit, which circuit is able to detect the presence of a carrier on the transformer secondary winding. In receipt mode, the switch is closed and the control circuit analyzes the modulated information received on the transformer secondary winding. In transmission mode, the control circuit causes switching of the switch at the information modulation frequency (132 khz), performing both power supply of the control circuit and transmission of the information.

A limiter switching apparatus includes a control box adapted for being mounted on a machine table with a plurality of terminals and indicators for making electrical connections; and an interface circuit device installed in the control box and electrically connected to the terminals and indicators for effecting switching operations. The interface circuit device is composed of a lower supply circuit for supplying minimal current and voltage therefrom, a first switching circuit connected to the power supply circuit for being actuated to turn on and off, a limiter switch circuit coupled with the first switching circuit and the power supply circuit for controlling the on and off of the first switching circuit, and a second switching circuit with a relay arrangement electrically connected to the power supply circuit and optically coupled with the first switching circuit for effecting relaying operations along with the on and off of the first switching circuit, thereby, safe switching operations with minimal current and voltage can be ensured without incurring electrical leakage from water and oil damage.