Call cost meter for telephone equipment - is inductively coupled to telephone via coil at input of amplifier-demodulator system

摘要

The call cost meter, for telephone equipment, has an induction coil (1, 2) coupled inductively outside the telephone housing to the telephone transformer and connected to the input of an amplifier and demodulator circuit (4-20, 22) responding to the timing pulse frequency. The amplifier/demodulator circuit drives a pulse counter (21). The induction coil forms part of a resonant circuit (1-3) at the input of the amplifier/demodulator circuit and tuned to the timing pulse frequency. The advantage lies in cheapness and in not needing to be installed permanently in the telephone.