Multiple device control system

Abstract

A train communication and control system is described having the cars of the train connected by a two-wire train line running continuously from car to car. Each car has a transmitting circuit and a receiving circuit connected across the line. Any car may be selected to be a master unit. The selection of one car as a master unit disconnects the power sources of all other cars from the train line, leaving the master unit power source as the sole power source for the line. The master unit or any other car unit communicates with each other car by causing a high voltage ('mark' state or logic one) or a low voltage ('space' state or logic zero) to be on the train line. Each non-master car can receive a communication from a transmitting circuit, or can transmit to another car by applying a low impedance across the train line to change from a 'mark' state to a 'space' state. The power source consists of a voltage regulator with precision constant current limit. Output voltage is maintained substantially constant until a load greater than the rated current limit causes the power source to change to a substantially constant current regulator, whereby its regulated voltage falls rapidly to the 'space' state voltage.