Key telephone lamp control circuit

Abstract From the Canadian patent

Abstract of the Disclosure, There is disclosed an electronic key telephone line circuit having a communication path interface capable of being connected across the communication pair during both the busy and idle conditions of the line circuit. The circuit is arranged such that both the pre-ring test and the impedance test from the central switching machine are satisfied while at the same tome presenting a linear impedance for communication signals. Opto isolators are used and coupled with lightening surge protection and a capacitance and resistance bridge to allow permanent connection across the communication pairs. The circuit includes a hold bridge impedance, separate from the signal …