Interface connecting TV receiver to video text data-bank - monitors telephone line for loop or ringing currents before exciting connection relay

摘要

The interface monitors the telephone line for the presence of a loop current and/or ringing current and passes the result to the television receiver. The monitor is located in one of the telephone wires and is connected to a third wire that passes to the television receiver. The monitor contains a bridge rectifier with a capacitor, transistor and voltage divider. the output side of the bridge is connected to the input of an optoelectronic coupler that provides electrical decoupling between the interface and the third wire leading to the television receiver.