Alarm circuit operated via telephone line

摘要

The circuit provides an emergency alarm system which only uses the telephone supply voltage of 60V to realise the supply voltage for the alarm control. In the rest position, only a minimal part of the alarm circuit is supplied with quiescent current less than or equal to 1 mA. For the alarm, the whole of the control is supplied with the operating voltage (Up1,Up2) via a voltage switch (SA). Timing elements (T1, T2, T3) are connected to the alarm circuit to make a definite output condition and for freeing the telephone line (a, b). The operating status, dial pulse sequence and connection to the telephone line (a, b) can be visually displayed on the device by a lamp.