Telephone signaling circuit

Abstract From the Canadian patent

Abstract: A telephone signaling interface enables compatible communications between a telephone station set and a key telephone system. Separate alternating voltage control signals from the key telephone system are amplitude and polarity modulated and combined by the interface to provide ringing, switchook supervision and visual signaling to station set over a single signaling wire pair. Current flow on the signaling pair in one direction provides visual signaling while distinguishable amounts of current flow in the opposite direction provide the supervision and ringing signals. Interruption of the supervision current is converted by interface into an "A" lead supervision signal for the key …