Telephone line status detector - has blocking diode earthing resistor, switch and indicators in exchange

摘要

An electronic unit to detect the status of a telephone line, and also supply a call current can detec when the line loop is closed. It can also detect the earthing of the line and when a receiver has been lifted. The unit has a circuit with a blocking diode in the telephone line. A blocking voltage is applied o the diode. A blocking switch is also used during the supply of the call current. Indicators are connected to the unit. These indicators are part of an exchange. The call connectors are opto electronic connectors, each in a diode bridge arm. The photodetectors are controlled rectifiers.