Often, unauthorized people use the phone to make improper calls. A control for this is achieved with the circuit that we present. Adapting a plug to the telephone socket, Telebrás standard (4 pins), a modification is made by “jumping” the pins, according to the same design, in order to make it an interchangeable and portable two-pole on-off switch. Thus, the TM1 and TM2 sockets are modified so that L1 and L2 are connected to the TM3 socket on the main telephone, which does not appear in this drawing. To better understand the operation, we have in the second figure a suggested panel with the arrangement of TM1 and TM2 sockets installed. For them to work, the J1 plug must be connected to one of them: TM1 or TM2, together with the cord plug of the telephone set.
