Circuit preventing shared telephone being engaged by two calls - applies blocking potential to all switching circuits not involved so that only one can be active at any time

摘要

The circuit prevents a shared telephone being engaged by two or more calls simultaneously by applying a blocking potential to all switching circuits not involved, ie only one switching circuit an be active at any time. This is achieved by inter-connecting all switching circuits and blocking gates so that they are interdependent. The advantage lies in requiring the same circuitry per terminal (coupled to the shared device being protected) irrespective of the number of terminals coupled to the device. The common transistor (T3) is controlled via the diode (D11) and resistor (R8). The common transistor (T3) controls the transistors (T12, T22... Tn2) via the resistors (R17, R27... Rn7).