Call unit for telephone equipment - has loop detector and logic circuit to excite telephone equipment call signal generator

摘要

A call unit for telephone is used with electronic exchanges which generate high frequency low energy signals for tone calls. The unit is part of a line unit connected to a telephone by two lines, and to a telephone network, to a control unit and to a call signal generator. The unit has a loop detector circuit comprising a comparator to detect the open or closed condition of the lines. It also has a circuit with transistors to excite the call signal generator. A logic circuit with a gate is used to control the transistor circuit.