GB1055596A - Improvements in or relating to telephone answering machines - Google Patents

Abstract

1055596 Telephone answering machines SHIPTON ELECTRONICS Ltd 15 Oct 1963 [15 Oct 1962] 38936/62 Headings H4R and R25 A telephone answering machine is provided with a circuit, shown in the Figure, which by the operation of relay 1 closes down the answering machine either after speech signals have ceased for a predetermined time or when a continuous tone signal, i.e. dialling tone, is received. The operation of the circuit is as follows:- line signals are applied to the base of transistor 3 which forms part of a speech detector circuit, speech signals causing transistor 3 to conduct maintaining capacitor C1 in a partially discharged state. If speech signals cease capacitor Cl will charge and via diode 4 and relay amplifier 2 will operate closing down relay 1, the time constant of charging being such that the relay operates if the gap in the speech is of 15 seconds duration. The line signals are also applied to the base of transistor 5 in the tone detector circuit, speech signals tending to discharge capacitor C2 which will, however, charge up during gaps in the speech and, since it has a short charging time constant, e.g. about 100 milliseconds, transistor 6 will conduct and so maintain capacitor C3 partially discharged. If a tone signal is present on the line, however, transistor 5 will conduct continuously, cutting off transistor 6, and allowing capacitor C3 to charge to such a potential as to energize the relay amplifier 2 and cause closing down of the machine, the charging time constant of C3 being 3 to 4 seconds.