Electronic switching system

Abstract

This report documents briefly the work undertaken to construct a small private telephone exchange. This field of' communications has undergone a revolution by the introduction of new techniques. The aim of' this project was to gain insight into this technology by actually building an experimental prototype. This was designed to have a fully electronic analogue cross point switching matrix and microprocessor based stored program control. The hardware and software were developed with the help of a BBC computer. At a later stage, a dedicated CPU card was designed so that the exchange alone unit. could function as a stand At the time of writing, the system can handle four extension lines with two digit pulse dialling, and one trunk line. Incoming calls were routed to a particular extension so that an operator was not necessary. There is also provision for a remote bell and a further four loops which could be used to monitor on-off circuits. This restricted outlay was dictated by the limited budget and time and because of' the inherent experimental nature of the project.