Multiple device control system

A communication system comprising

• a transmitting circuit,
• a receiving circuit,
• a two-wire line connecting said circuits,
• a single voltage source connected across said line for supplying voltage to said line,
• means for transmitting from said transmitting circuit to said receiving circuit binary information in the form of a sequence of binary bits of two types representing marks and spaces of a binary signal, comprising means at said transmitting circuit for applying a low impedance shunt across said line to reduce the voltage at said receiving circuit in correspondence with each occurrence of a bit of said binary information of one type,
• said voltage source having means maintaining both a substantially uniform voltage for loads across said line having a range of impedances greater than said low impedance and a substantially constant current for loads across said line having a range of impedances substantially equal to or less than said low impedance.

A communication system for a multi-car train comprising

• a plurality of spatially separated units, each unit comprising
• (a) a communication line section consisting of two continuous galvanically conductive wires, the line section of each unit being galvanically connected serially to the line sections of all other units to form a single two-wire line for all units,
• (b) a transmitting circuit, and
• (c) a receiving circuit,
• each of said transmitting circuits and receiving circuits being connected in parallel across said line at its respective location whereby all said circuits are connected directly to said two wires,
• a single direct voltage source connected across said line at one point thereof and providing the only source of voltage on said line,
• each transmitting circuit comprising means for causing the voltage on said line produced by said voltage source to vary at all points along said line between a high level and a low level in correspondence with a binary signal to be transmitted,
• each of said units being in a separate train car, and said two-wire line extending serially from car to car along said train from one end of the train to the other,
• each car of the train having a said transmitter and a said receiver, said voltage source being coupled across said line at a selected (master) car, said line having no other voltage or power sources connected to said line,
• said voltage-varying means comprising means at each transmitter to apply a shunt to said line in accordance with one bit of a binary signal to increase the current in said line from said voltage source and to reduce the voltage across said line at the receivers of all cars during such shunting, and
• each receiver having means to respond to said voltage reduction to detect said signal.

A communication system comprising

• a plurality of spatially separated units, each unit comprising
• (a) a communication line section consisting of two continuous galvanically conductive wires, the line section of each unit being galvanically connected serially to the line sections of all other units to form a single two-wire line for all units,
• (b) a transmitting circuit, and
• (c) a receiving circuit, and
• (d) a direct voltage source,
• each of said transmitting circuits and receiving circuits being connected in parallel across said line at its respective location whereby all said circuits are connected directly to said two wires,
• a single one of said voltage sources being connected across said line at one point thereof and providing the only source of voltage on said line,
• each transmitting circuit comprising means for causing the voltage on said line produced by said voltage source to vary at all points along said line between a high level and a low level in correspondence with a binary signal to be transmitted,
• all said receiving circuits being adapted to respond to variation of voltage on said line caused by a transmitting circuit of one unit, to reproduce said signal,
• and means assuring that at any time only a selectable one of said voltage sources is connected to said line and that all other voltage sources are concurrently disconnected from said line.

A communication system comprising

• a plurality of spatially separated units, each unit comprising
• (a) a communication line section consisting of two continuous galvanically conductive wires, the line section of each unit being galvanically connected serially to the line sections of all other units to form a single two-wire line for all units,
• (b) a transmitting circuit,
• (c) a receiving circuit, and
• (d) a ground
• each of said transmitting circuits and receiving circuits being connected in parallel across said line at its respective location whereby all said circuits are connected directly to said two wires,
• a single direct voltage source connected across said line at one point thereof and providing the only source of voltage on said line,
• each transmitting circuit comprising means for causing the voltage on said line produced by said voltage source to vary at all points along said line between a high level and a low level in correspondence with a binary signal to be transmitted,
• all said receiving circuits being adapted to respond to variation of voltage on said line caused by a transmitting circuit of one unit, to reproduce said signal,
• and means assuring that at any time only a selectable one of said grounds is connected to one wire of said line and that all other grounds are disconnected from said line.

A communicating system for a plurality of spatially separated units,

• said units being interconnected only by a single line formed of two continuously conductive wires,
• each unit comprising (a) a voltage supply circuit adapted to supply voltage to said line, (b) a transmitting circuit, and (c) a receiving circuit,
• the transmitting circuit and receiving circuit of each unit being continuously connected across said two-wire line,
• means at each unit for causing its voltage supply circuit to be connected across said line, and
• means operative upon connection of one voltage supply circuit to said line for causing the voltage supply circuit of all other units to be disconnected from said line, whereby said entire line is supplied from only one voltage supply circuit at any time.

A train communication system having cars of the train connected directly by a two-wire train line running continuously and conductively from car to car, each car having a power source, a receiver and a transmitter comprising:

• means for causing any car to be a master unit and for concurrently disconnecting the power sources of all of the other cars from said train line, leaving the master unit power source as the sole power source for the line,
• means for causing the master unit to apply to said line a high voltage representing a binary bit of a first type of a binary digital signal to be transmitted,
• the transmitter in each car being coupled to said train line and being adapted to apply a low impedance across the train line to change the voltage on the train line from a value representing said first type bit to a lower value representing a second type binary bit, in correspondence with said binary digital signal,
• the receiver in each car being coupled to said train line and being adapted to receive said signal.

A message display system comprising:

• a plurality of message display devices,
• a two-wire communication line,
• a plurality of sign control units, each at a different location, and each associated with one or more of said display devices at a respective location, said sign control units being connected to one another solely by said two-wire communication line,
• each sign control unit comprising a voltage supply whose output is coupled across said line, an operator's control, a transmitting circuit whose output is coupled across said line, a receiving circuit whose input is coupled across said line, and a microprocessor,
• means responsive to actuation of said operator's control at one location for causing the microprocessor at said location to activate the voltage supply at that location to cause the sign control unit at that location to become a master unit and to disconnect the voltage supplies at all other locations from said line to cause the sign control units at said other locations to become slave units, said activated voltage supply being connected to said communication line as the sole source of power for said line.

A communication system comprising

• plurality of spatially separated units, each unit comprising
• (a) a communication line section consisting of two continuous galvanically conductive wires, the line section of each unit being galvanically connected to the line sections of all other units to form a single two-wire line for all units,
• (b) a transmitting circuit, and
• (c) a receiving circuit,
• each of said transmitting circuits and receiving circuits being connected in parallel across said line at its respective location whereby all said circuits are connected directly to said two wires,
• a single direct voltage source connected across said line at one point thereof and providing the only source of voltage on said line,
• each transmitting circuit comprising means for causing the voltage on said line produced by said voltage source to vary at all points along said line between a high level and a low level in correspondence with a binary signal to be transmitted,
• all said receiving circuits being adapted to respond to variation of voltage on said line caused by a transmitting circuit of one unit, to reproduce said signal.