Dual mode telephone subscriber loop current detector

Abstract From the Canadian patent

Abstract of the Disclosure, A detector circuit is shown for detecting offhook and dial pulse signals in a telephone system which under the control of a ringing relay, reconfigures itself to provide ring-trip detection. The detection circuit includes a bridge which is responsive to circulating loop currents while at the, same time unresponsive to longitudinally balanced currents, and a two-stage voltage level detector circuit. An RC timing circuit is included between the two stages to insure that the detector is unresponsive to short duration pulses and, at the same time, once energized will bridge over short duration interruptions of detected pulses. - i -