Dialling bar for a telephone device

摘要

A dialling bar for a telephone device, with a talk-listen device (HS) connected to the telephone line (a, b), upstream of which a hook switch contact (GU) and the contact (nsi) for generating the dial pulses are connected. The dialling bar can be activated and de-activated by means of a key-operated switch (S). The first arm (a2) of the telephone line is connected to the second arm (b) via an arm which is disposed in parallel with the telephone device (2) and which contains a controllable electronic switch (Tr). Furthermore, a voltage-sensing device (M) which is connected to the first arm (a2) of the telephone line transmits, in the event of a voltage change on this arm, a control pulse of pre-defined duration and size which is fed to the controllable electronic switch (Tr) and through-connects it for the duration of the pulse. In this way, the loop interruption produced during the generation of dial pulses is counteracted by the closure of the parallel arm and no dial pulse is transmitted (Fig. 1). <IMAGE>