schaltungsanordnung for a small fernsprechnebenstellenanlage (heimtelefonanlage) with house and amtsverkehr on a amtssatz

摘要

A telephone system for installation in a home allows one main and four extensions to make internal calls or use the exchange line, and is controlled by a microprocessor. An outside call can be made or received on any telephone while others are engaged on an internal call. An internal call cannot be made, however, if an outside call is already in progress. Two busbars are provided, each with its own hybrid transformer and power supply. All telephones are normally on the house busbar but are switched to the exchange busbar while setting up internal calls or for outside calls. If the house power supply fails, the system is bypassed and the main switched direct to the exchange line. The microprocessor detects lifting or replacing a receiver and dial pulses by means of an opto coupler connected in one wire to each telephone.