Noise Proof Analog Detection of a Ground Button Procedure
Original Publication Date: 1978-Jan-01
Included in the Prior Art Database: 2005-Feb-20
In an extension circuit, the ground button procedure consists in grounding the a and b wires of the telephone set in order to call the operator. The detection of this action raises problems since longitudinal AC voltages may be present on the line and create confusion with the quasi-permanent signals generated by a subscriber when pushing the ground button of his telephone set.