Ring detection circuit for a telephone answering device

Abstract

A ring responsive circuit useful with a telephone answering device employs a single low inductance transformer both to couple audio to the telephone line and in the ring responsive circuit. A voltage doubler and neon bulb effectively capacitively couple the transformer primary to the telephone line. When a ring signal occurs, the doubled voltage fires the neon bulb on alternate half cycles of the ring signal. The resultant fast rise time current transients contain high frequency components that are coupled by the same transformer to the secondary. There, they repetitively momentarily turn on a transistor, as a result of which a bistable circuit is latched on. When on, the latch circuit connects dc power to the motor, amplifiers and other circuitry of the telephone answering device, and to the coil of a relay the contacts of which shunt the voltage doubler circuit and directly connect the transformer primary to the telephone line so as to seize the line and begin the answering cycle.