Auxiliary circuit for control of telephone bell - has semiconductor circuit determining activation by code,申请号IT19760047904-传众专利搜索

Auxiliary circuit for control of telephone bell - has semiconductor circuit determining activation by code

申请公布号：IT1053904(B)

申请号：IT19760047904

申请日期：1976.02.02

申请公布日期：1981.10.10

申请人：

INTERTEL II INC

分类号：H04M;(IPC1-7):04M/

主分类号：H04M

摘要：<p>An auxiliary circuit for a telephone system where the bell can be selectively activated by using a particular code. This is intended to avoid undesirable calls, while recognising desirable calls immediately. The circuit can be incorporated in a two-wire system. The two wire of the telephone (12, 14) are connected to a bridge rectifier (16, 18, 20, 22). The lines joining the diode contain a capacitor (34) and a resistor (38), which is connected to a flip-flop circuit which operates the switching. The resistance (38) is also coupled to a transistor (42) which is in series with a normally closed relay (44). The circuit is coupled to a detector which picks out a component frequency of a signal by determining the difference between the frequency of the component and the frequency of a local oscillator.</p>