U.S. patent number 3,828,307 [Application Number 05/157,871] was granted by the patent office on 1974-08-06 for automatic traffic control system.
This patent grant is currently assigned to Georgia Tech Research Institute. Invention is credited to Ernest Timmons Hungerford.
United States Patent |
3,828,307 |
Hungerford |
August 6, 1974 |
AUTOMATIC TRAFFIC CONTROL SYSTEM
Abstract
An automated control system is disclosed that is particularly
adapted for use in regulating urban traffic flow. The system
includes a central control facility linked with a plurality of
remote terminals over a unitary communication channel, which is
preferably equivalent to a voice grade, non-compensated telephone
line. The central control facility includes a computer coupled
through interface equipment with a master transceiver. The master
transceiver couples the computer and interface equipment with the
communication channel. Each of the remote terminals, which are
coupled to the communication channel in parallel, party line
fashion, includes a remote transceiver coupled through interface
equipment to a traffic control device, such as a signal light. An
emergency vehicle locator may also be included in each remote
terminal. Vehicle detectors may be coupled to the communication
channel through the remote terminals or through separate remote
transceivers to provide a measure of traffic flow parameters.
Inventors: |
Hungerford; Ernest Timmons
(Atlanta, GA) |
Assignee: |
Georgia Tech Research Institute
(Atlanta, GA)
|
Family
ID: |
22565639 |
Appl.
No.: |
05/157,871 |
Filed: |
June 29, 1971 |
Current U.S.
Class: |
340/909; 340/915;
340/931 |
Current CPC
Class: |
G08G
1/087 (20130101); G08G 1/081 (20130101) |
Current International
Class: |
G08G
1/081 (20060101); G08G 1/087 (20060101); G08G
1/07 (20060101); G08g 001/08 () |
Field of
Search: |
;340/35,37,40,41 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Computer-Controlled Vehicular Traffic," Gordon D. Friedlander,
IEEE Spectrum, February 1969, pages 30-43. .
IBM Technical Disclosure Bulletin, M. Druckerman, Vol. 7, No. 3,
August 1964, pages 211 & 212..
|
Primary Examiner: Claffy; Kathleen H.
Assistant Examiner: Myers; Randall P.
Attorney, Agent or Firm: Newton, Hopkins & Ormsby
Claims
What is claimed as new and desired to be secured by Letters Patent
of the United States is:
1. An automated traffic control system comprising:
a central control facility, said central control facility including
computer means for processing input information signals and for
generating traffic control signals, and
computer interface means in said central control facility coupled
to said computer for applying said input information signals to
said computer means and for transmitting said traffic control
signals from said computer means;
signal communication means in said central control facility, said
signal communication means coupled to said interface means and
including multiplexing means;
a single communication line coupled to said signal communication
means for transmitting signals to and from remote points; and
a plurality of remote terminal means coupled to said single
communication line in parallel, party-line fashion for receiving
said traffic control signals from said computer means and for
supplying said input information signals to said computer means
over said single communication line.
2. An automated traffic control system as in claim 1, wherein: said
communication line includes a voice grade, non-compensated
communication line.
3. An automated traffic control system as in claim 1, wherein:
said computer means comprises a digital computer facility.
4. An automated traffic control system as in claim 1, wherein:
said signal communication means includes
master transceiver means coupled to said communication line for
transmitting signals over and receiving signals from said
communication line.
5. An automated traffic control system as in claim 4, wherein:
said computer interface means includes input-output storage
register means for temporariliy accumulating signals to be fed into
said computer means and for temporariliy accumulating signals
generated by said computer means.
6. An automated traffic control system as in claim 4, wherein:
said master transceiver means includes a coarse synchronization
signal generating means for conditioning said remote terminal means
to receive a synchronization signal.
7. An automated traffic control system as in claim 4, wherein:
said master transceiver means includes a fine synchronization
signal generating means for preparing said remote terminal means to
receive and decode data from said central control facility.
8. An automated traffic control system as in claim 4, wherein:
said master transceiver means includes means for generating a
stable carrier reference for enabling said remote terminal means to
decode data transmitted from said central control facility.
9. An automated traffic control system as in claim 4, wherein:
said master transceiver means includes means for establishing a
data input gate interval for defining a period during which data is
transmitted from said central control facility to said remote
terminal means.
10. An automated traffic control system as in claim 4, wherein:
said master transceiver means includes means for establishing a
data response gate interval for defining a period during which data
is transmitted from said remote terminal means to said central
control facility.
11. An automated traffic control system as in claim 4, wherein:
said master transceiver means includes said multiplexing means for
permitting time shared use of said communication line.
12. An automated traffic control system as in claim 4, wherein:
said remote transceiver means includes means for recognizing only
traffic control signals which are directed uniquely to a particular
one of said remote transceiver means.
13. An automated traffic control system as in claim 1, wherein:
Said remote terminal means include remote transceiver means coupled
to said communication line for transmitting signals over and
receiving signals from said communication line.
14. An automated traffic control system as in claim 13,
wherein:
said remote terminal means include traffic control means for
regulating traffic flow; and,
terminal interface equipment for coupling said traffic control
means with said remote transceiver means.
15. An automated traffic control system as in claim 14,
wherein:
said central control facility includes a visual display means for
displaying the various conditions of said traffic control
devices.
16. An automated traffic control system as in claim 14,
wherein:
said remote terminal means include local controller means for
controlling the operation of said traffic control means according
to a self-contained predetermined program.
17. An automated traffic control system as in claim 16 wherein:
said remote terminal means include emergency vehicle detector means
for sensing the presence of emergency vehicles; and,
said terminal interface equipment includes means for disabling said
local controller means in response to the detection of an emergency
vehicle by said emergency vehicle-detector means.
18. An automated traffic control system as in claim 17,
wherein:
said remote terminal means includes sequencing means for rendering
said mean for disabling said local controller means inoperative
until after a prescribed signal is received from said central
control facility.
19. An automated traffic control system as in claim 17,
wherein:
said terminal interface equipment includes means for causing said
traffic control means to produce a signal indicative of the
presence of an emergency vehicle.
20. An automated traffic control system as in claim 14,
wherein:
said traffic control means include indicator lamp means for
producing visual traffic regulating signals.
21. An automated traffic control system as in claim 14,
wherein:
said remote terminal means include signal generator means for
generating a signal in response to said traffic control means
becoming inoperative.
22. An automated traffic control system as in claim 13,
wherein:
said remote terminal means include vehicle detector means coupled
to said remote transceiver means for measuring parameters of
traffic flow.
23. An automated traffic control system as in claim 13,
wherein:
said remote terminal means include emergency vehicle detector means
coupled to said remote transceiver means for sensing the presence
of emergency vehicles.
24. An automated traffic control system as in claim 13,
wherein:
said remote transceiver means includes data receiver means for
accepting said traffic control signals from said central control
facility.
25. An automated traffic control system as in claim 24,
wherein:
said remote transceiver means includes coarse synchronization
signal detecting means for preparing said data receiver means to
receive traffic control signals from said central control
facility.
26. An automated traffic control system as in claim 24,
wherein:
said remote transceiver means includes fine synchronization signal
detecting means for preparing said data receiver means to decode
traffic control signals from said central control facility.
27. An automated traffic control system as in claim 26,
wherein:
said fine synchronization signal detecting means includes means for
establishing a stable reference signal for demodulation of said
traffic control signals from said central control facility.
28. An automated traffic control system as in claim 27,
wherein:
said fine synchronization signal detecting means includes phase
sensitive means for determining whether said stable reference
signal is in phase with a signal from said central control
facility, or 180.degree. out of phase with said signal from said
central control facility.
29. An automated traffic control system as in claim 27,
wherein:
said remote transceiver means includes response modulator means for
producing pulse amplitude modulation of said stable reference
signal.
30. An automated traffic control system as in claim 13,
wherein:
said remote transceiver means includes logic means for
demultiplexing said traffic control signals from said central
control facility and for multiplexing said input information
signals for transmission to said central control facility.
31. An automated traffic control system as in claim 13,
wherein:
said remote terminal means include vehicle sensing means for
detecting the presence of vehicles.
32. An automated traffic control system as in claim 13,
wherein:
said remote terminal means include vehicle counting means for
determining the number of passing vehicles.
33. An automated traffic control system as in claim 13,
wherein:
said remote terminal means include vehicle speed detectors for
determining the speeds of passing vehicles.
Description
BACKGROUND OF THE INVENTION
1. Field Of The Invention
This invention relates generally to communication networks, and
more particularly to an automatic communication system for use in
traffic control.
2. Description Of The Prior Art
In metropolitan areas with populations greater than 100,000, the
vehicular traffic and transportation environment is becoming more
complex, and satisfactory control of vehicular traffic flow
presents many problems. In some areas attempts are being made to
solve the varied problems by implementation of centralized,
computer operated traffic control systems. Whether the computer
utilized is analog or digital, significant problems exist in
providing adequate communications between the central facility and
the individual traffic control devices which are located on the
street.
Most existing systems require essentially one dedicated line of
communications from the central facility to each individual remote
traffic control device. A remote traffic control device may be a
conventional signal light or traffic light located at a highway or
street intersection, for example. Naturally, in any city of
reasonable size, hundreds, or perhaps thousands of such individual
signal lights are required to keep traffic flowing smoothly.
Consequently, hundreds or thousands of individual communication
lines are required, to make such presently existing systems
operational.
In addition, where various types of vehicle detection devices are
utilized, individual communication lines are also required for
these units. Vehicle detection devices may detect the presence of a
vehicle or measure other data related to vehicular traffic flow,
such as vehicle speed. Vehicle detection devices may be located on
the streets immediately adjacent to an intersection or they may be
spaced along a street or arterial. The data furnished by vehicle
detection devices may be utilized in a computer facility to
establish, compute, or select a desired traffic flow plan for the
indicated traffic conditions.
In any centralized traffic control system, this current practice of
utilizing a single, dedicated communication line to each traffic
control device or vehicle detector can be extremely expensive and
can result in the need for a large amount of complex interface
equipment. The initial installations of the many separate
communication lines required are also costly. In addition, if the
lines are leased from the local Telephone Company, the continuing
lease costs of many lines can be significant, particularly for the
larger systems.
Consequently, there is a need for an automated traffic control
system that includes an efficient and relatively inexpensive
communication link between its central control facility and each
remote traffic control device and vehicle detector.
SUMMARY OF THE INVENTION
Accordingly, one object of this invention is to provide a novel
automated traffic control system which includes a highly simplified
communication network.
Another object of this invention is to provide an automated traffic
control system including a communication network which is
relatively inexpensive to maintain.
Yet another object of this invention is to provide an automated
traffic control system including a communication network which is
relatively simple and inexpensive to install.
A further object of this invention is to provide an automated
traffic control system in which the central control facility is
linked to a plurality of remote traffic control devices and vehicle
detectors over a single communication line.
Another object of this invention is to provide a novel computer
controlled automated traffic control system.
A still further object of this invention is to provide an automated
traffic control system having novel remote terminal systems.
Yet another object of this invention is to provide an automated
traffic control system including emergency vehicle locators.
Another object of this invention is the provision of an automated
traffic control system which expedites the travel of emergency
vehicles in urban areas.
Briefly, these and other objects of the invention are achieved by
providing a central control facility including a computer linked
through interface equipment to a master transceiver. The master
transceiver is coupled to a communication link, which is preferably
equivalent to a voice grade, noncompensated telephone line, and
controls the flow of information over the communication link. A
plurality of remote terminals are coupled in parallel, party line
fashion to the communication link throughout an urban area. Each
remote terminal may include a remote transceiver and interface
equipment which may be coupled to a traffic control device, as well
as coupled to a vehicle detector or an emergency vehicle
locator.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the invention and many of the
attendant advantages thereof will be readily appreciated as the
same becomes better understood by reference to the following
detailed description when considered in connection with the
accompanying Drawings wherein:
FIG. 1 is a block diagram illustrating the general arrangement of
components in the automated traffic control system of the instant
invention;
FIG. 2 is a six-part timing diagram illustrating the operation of
the Master Transceiver of FIG. 1;
FIG. 3 is a four-part timing diagram illustrating the operation of
the Remote Transceiver illustrated in FIG. 1;
FIG. 4 is an expanded block diagram of the Modulator and Response
Receiver sections of the Master Transceiver of FIG. 1;
FIG. 5 is an expanded block diagram of the Logic section of the
Master Transceiver of FIG. 1;
FIG. 6 is an expanded block diagram of the Sync Detector, Data
Receiver and Response Modulator sections of the Remote Transceiver
of FIG. 1;
FIG. 7 is an expanded block diagram of the Logic section of the
Remote Transceiver of FIG. 1;
FIG. 8 is a block diagram of an output circuit which may be coupled
to the Logic section of the Remote Transceiver illustrated in FIG.
7;
FIG. 9 is an expanded block diagram of the first logic network
illustrated in FIG. 8;
FIGS. 10A, 10B and 10C illustrate is an exemplary circuit and logic
diagram for remote control of a six-street intersection;
FIG. 11 is an exemplary circuit and logic diagram illustrating on
an expanded scale a portion of the circuit of FIG. 10, showing a
remote control circuit for operating the indicator lights for one
street of the six-street intersection;
FIG. 12 is a circuit and block diagram illustrating a system for
expediting the travel of emergency vehicles;
FIG 13 is a circuit and block diagram illustrating a system for
controlling a simple two-street intersection;
FIG. 14 is a circuit and block diagram illustrating an interface
network for coupling response signals from traffic light indicators
at a given intersection with the associated remote unit;
FIG. 15 is a schematic diagram of an burn-out detection circuit;
and,
FIG. 16 is a block diagram of vehicle detector interface equipment
which may be used in the instant invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
I. GENERAL
Referring now to the Drawings, wherein like reference numerals
designate identical or corresponding parts throughout the several
views, and more particularly to FIG. 1 thereof, the instant
invention is shown as including a Central Facility 10 for the
control of traffic and transportation. Contained within the Central
Facility 10 are a Computer 12, Computer Interface Equipment 14, and
a Master Transceiver 16. If desired, a Visual Display Board 18 may
be utilized to indicate the current status of all remote traffic
devices 20, 30 and 32. The Master Transceiver 16 is connected to a
Communication Link 22, which includes a single communication line.
This line may be equivalent, for instance, to a voice grade,
non-compensated telephone line. Such a line can be connected
through a multiplicity of telephone exchanges if necessary. Also
other communication links identical to 22 can be operated from the
Master Transceiver 16, if desired.
Spaced along the communication line at arbitrary distances are
Remote Terminals 24 which are connected to the Communication Link
22 in parallel, party line fashion. Each Remote Terminal includes a
Remote Transceiver 26 for use with a locally attached Traffic
Control Device 20. The Remote Transceiver 26 includes Interface
Equipment 28 for coupling it to the attached Traffic Control Device
20. The Remote Transceiver permits appropriate remote control of
the Traffic Control Device as well as a locally controlled
operation of the Traffic Control Device. A Vehicle Detector 30 may
be connected locally through Interface Equipment 28 to a nearby
Remote Transceiver 26 to the Communication Link 22, or a separate
Remote Transceiver may be used to couple a Vehicle Detector to the
Communication Link 22. An Emergency Vehicle Locator 32, comprising
auxiliary receiver equipment, may be included in each Remote
Terminal 24 such that emergency vehicle information can be
appropriately transmitted through the Remote Transceiver 26 to the
Central Facility, when desired.
Within the Central Facility 10, the Computer 12 may be either
analog or digital. A digital computer is superior for the present
purpose since its possible applications are move varied and more
flexible. Based on input vehicular traffic data, the software
package of the Computer 12 can be constructed for computation of an
appropriate traffic control plan or for specific selection of one
of several programmed traffic control plans. The appropriate
control data are transmitted in the form of commands to each Remote
Transceiver. In addition, the computer facility can be utilized for
record keeping and appropriate production of hard copy records.
In the Central Facility 10, the Interface Equipment 14 has a
two-fold function: (1) It couples coded command data from the
Computer 12 to the Master Transceiver 16; and (2) it receives coded
response information from the Master Transceiver and couples this
data to the Computer.
In the Central Facility, the Master Transceiver equipment generates
all pulse timing and frequency information for operation of the
Communication Link 22. Appropriate timing signals are input to the
Computer 12 via the Interface Equipment 14. In addition, output
command data, via the Interface Equipment, are processed and
appropriately multiplexed onto one or more Communication Links.
Appropriate synchronization information is also generated in the
Master Transceiver 16 and appropriately multiplexed onto the
Communication Link 22.
At each Remote Terminal 24, the Remote Transceiver 26 is
appropriately coupled to the Communication Link 22 in parallel with
other remote units on the same communication line. Each remote unit
is automatically and periodically synchronized by means of the data
received from the Central Facility 10. For each remote unit, this
enables specific reception of its own command data. These commands
are demodulated and processed for application to the attached
Traffic Control Device 20, which may be conventional traffic
lights, for example. The locally processed data are coupled to the
attached Traffic Control Device by means of Interface Equipment 28.
This circuitry applies power to the appropriate lamp indicators of
the local Traffic Control Device. This same interface circuity is
responsive to the existent state of the lamp indicators. These
response signals are processed and coupled to the attached Remote
Transceiver 26, where they are further processed and modulated onto
the Communication Link 22. Appropriate reception of these response
signals occurs at the Central Facility 10, and furnishes one part
of the information input to the Computer 12.
In systems which utilize vehicle detection devices, a second
category of information can be input to the Computer 12. Data
gathered by a vehicle detection device of Vehicle Detector 30 may
be coupled by wire to a nearby Remote Transceiver 26 via Interface
Equipment 28 for subsequent transmission to the Central Facility
10. On the other hand, each vehicle detection device may be
utilized with its own Remote Transceiver. In either case, the data
are processed and appropriately multiplexed onto the Communication
Link 22 to be utilized by the Computer for generation or selection
of an appropriate traffic flow plan.
In systems where it is desired to locate emergency vehicles,
additional reciever circuitry 32 can be included with each Remote
Transceiver 26 at each controlled intersection. Sequential response
to emergency vehicles as they proceed through a controlled
intersection can be generated by the additional receiver circuitry.
This information can be processed and appropriately multiplexed
onto the attached Communiation Link 22. Emergency vehicle data
detected at the Central Facility need not be computer processed,
except for record keeping purposes. An appropriate Visual Display
Board as illustrated at 18 may be used for analyzing this
information
The remote control and associated processing of discrete data to
and from the Remote Terminals 24 can be accomplished by appropriate
time division multiplexing. The circuitry discussed herein is
relatively simple and inexpensive.
A timing diagram for the cyclic operation of the system as a whole
provides a description of the general system operation. Referring
now to FIG. 2, the Central Control Facility 10 time base is
depicted in part (a). Several count values and count periods are
indicated, which will be discussed subsequently in more detail. A
syn alert gate defined by each of pulses 34 and 36 is shown in part
(b ) of the figure. It is noted that the term "pulse" is used
merely as a convenient term designating the rectangular waveforms
shown in the Drawings. Transmitted data contained in this period
are utilized for arming of Remote Transceivers 26 for subsequent
sync reception. A data transmission gate defined by a pulse 38 is
shown in part (c) of the figure and extends for approximately
one-third of the total cycle time. All data from the Master
transceiver 16 are transmitted during this time, including sync
data and individual, discrete command data for each Remote Terminal
24. The syn gate defined by a pulse 40 is shown in part (d) of the
figure. During this time, precise synchronization data may be
transmitted in the form of a binary coded word. The data input gate
defined by a pulse 42 is shown in part (e) of the figure. It is
during this time that actual commands are transmitted to each
remote unit. The response interval defined by a pulse 44 is
depicted in part (f) of the figure. The extent of this interval
comprises essentially the remaining two-thirds of the total cycle
time. It is during this time that all data responses from all
Remote Terminals 24 are transmitted at the remote location and
received at the Central Facility 10. Vehicle Detector 30 responses
as well as Emergency Vehicle Locator 32 data may be included in the
response interval.
Referring now to FIG. 3, part (a), the time base of a Remote
Transceiver 26 is depicted. Local counts and count periods are
indicated which will be discussed subsequently in more detail. The
sync interval gate defined by a pulse 46 is shown in part (b) of
the figure. It is during this time that a Remote Transceiver 26 is
synchronized, first by coarse sync and second by fine sync signals.
The command interval gate defined by a pulse 48 is shown in part
(c) of the figure. It is during this time that the particular,
discrete command to a given Remote Terminal 24 is received,
demodulated, and processed. The response interval gate defined by a
pulse 50 is shown in part (d) of the figure. It is during this time
that an individual Remote Transceiver 26 processes and modulates
data for transmission back to the Central Facility 10.
Other procedural arrangements may be utilized with respect to time
sharing on a communication link. For instance, an individual
command could be transmitted to the first Remote Terminal or unit.
This first Remote Terminal could then respond to the received
command and transmit the response back to the Central Facility 10.
A second command could then be transmitted to the second Remote
Terminal over the same communication line used with the first
Remote Terminal. This process would be repeated for each attached
Remote Terminal. However, in the preferred embodiment, the
procedures refer to a time base construction similar to that
depicted in FIGS. 2 and 3.
II. TIMING BASE DESCRIPTION FOR PREFERRED EMBODIMENT OF
THE COMMUNICATION LINK SYSTEM
The communication cycle is a serial operation comprised of
synchronization signals and commands, which are transmitted from
the Central Facility 10, and response signals, which are
transmitted from the Remote Transceivers 26. In a Remote Terminal
24, the particular command to the Remote Terminal is detected and
stored during each communication cycle. The cycle length can be
changed or adjusted for any practical extent in time. This cycle
length is not directly related to the cycle times of traffic signal
devices, and in general, the communication cycle time is less than
a few seconds, while a traffic signal device cycle time may extend
for many seconds, perhaps minutes. On the other hand, it is
possible to maintain absolute timing of an attached Traffic Control
Device to less than one second.
The Central Facility time base shown in FIG. 2 will be described in
greater detail. This time base may be incremented, for instance, at
a rate of 3,600 Hz, determined from a master crystal-controlled
oscillator to be described hereinafter. The start of a
communication cycle occurs at count 0, referenced as t.sub.0 in
FIG. 2(a), and extends for 7,610 counts. Count 7611 is coincident
with count 0, at which time the master counter is reset to zero,
and the cycle repeats.
After activation of the Communication Link 22 and towards the end
of each communication cycle, a Sync Alert Gate pulse 34 occurs.
This is shown in FIG. 2(b) and occurs from count 7251 to count
7301. During this time interval, a low frequency tone may be
transmitted, for instance, 750 Hz. This tone may be utilized to
signal all attached Remote Transceivers 26 that a synchronization
interval will occur as the next event. Reception and detection of
this frequency tone in each Remote Transceiver may be considered as
establishment of coarse synchronization.
At count 7301, the Data Transmit Gate pulse 38 occurs. This gate is
shown in FIG. 2(c) and extends through count 0 to count 2301.
During the first part of this gate, a string of binary zones may be
transmitted at the carrier frequency to count 30. Reception and
direction of this signal in each Remote Transceiver establishes a
stable carrier reference for subsequent data decoding.
A Sync Gate pulse 40 occurs from count 30 to 51 as shown in FIG.
2(d). During this interval a fine-sync code word may be transmitted
at the carrier frequency. Reception and detection of the fine-sync
word in each remote unit may be considered as establishment of fine
synchronization.
A Data Input Gate pulse 42 occurs from count 51 to count 2301, as
shown in FIG. 2(e). During this interval, all command data are
transmitted from the Central Facility 10 to all attached Remote
Terminals 24.
A Response Gate pulse 44 occurs from count 2301 to count 7251, as
shown in FIG. 2(f). During this interval, all response data are
transmitted from all attached Remote Terminals to the Central
Facility 10.
A typical Remote Transceiver 26 time base is depicted in FIG. 3(a).
A remote time base may be referenced to the Central Facility 10
time base by establishment of the time T.sub.O. For instance, a
remote unit clock circuit (to be described hereinafter) may be
operated at 1,200 Hz. This frequency also may be established as the
bit rate. If this bit rate is utilized, the remote clock pulses
will occur at one-third the rate of the Central Facility clock
pulses.
In a remote unit, reception and detection of the low frequency tone
automatically establishes a sync interval as depicted by a pulse 46
in FIG. 3(b). Subsequent reception and detection of the reference
carrier signal and the fine-sync code word establishes T.sub.O in
each Remote Transceiver. At this time, a Remote Transceiver counter
is reset to zero.
The total command interval for a Remote Transceiver occurs from
T.sub.O to count 750, as shown by a pulse 48 in FIG. 3(c). The
total response interval for a Remote Transceiver occurs from count
750 to count 2400, as shown by a pulse 50 in FIG. 3(d).
Approximately at the time of count 2400, a given Remote Transceiver
will receive the low frequency Sync Alert Tone, and the
communication cycle will repeat.
The command data for all attached Remote Terminals are transmitted
from the Central Facility commencing at count 51, FIG. 2(a). These
data are transmitted serially in the form of binary ones and zeros.
The command data to any particular Remote Transceiver may comprise,
for instance, two, three, four, or five bits. The first bit
indicates the mode of control for a particular Remote Transceiver.
Thus, a binary one for the first bit signifies the Remote Control
Mode, and the particular remote unit will permit the attached
traffic signal device to be controlled by commands issued at the
Central Facility. If the first bit is a binary zero, the Local
Control Mode is indicated, and the particular remote unit will
cause the attached traffic signal device to be controlled by the
Local Controller at the Traffic Control Device.
If the first bit is a binary one, the remaining one, two, three, or
four bits may consist of some combination of binary ones and zeros.
Dependent on the number of required functions of the attached
traffic signal device, these remaining one, two, three, or four
bits may be utilized to convey, respectively, two, four, eight, or
16 discrete commands. Therefore, the associated Remote Transceiver
26 may be adjusted to accept its own required number of command
bits. Correspondingly, the command interval allotted to a given
remote unit must be at least equal in extent to the required number
of command data bits.
The response signals from each remote unit represent the existent
state of any attached traffic device. Thus, the response signals
can represent the existent state of on-the-street lamp indicators
for an attached traffic signal device, or the existent state of a
vehicle detection device, or information relating to the presence
of a particular emergency vehicle.
III. DESCRIPTION OF PREFERRED MASTER TRANSCEIVER CIRCUITRY FOR
THE COMMUNICATION LINK SYSTEM
The Master Transceiver 16 may comprise, for instance, a Modulator
52, a Response Receiver 54, and a Logic section 56. Block diagrams
of the Modulator 52 and Response Receiver 54 sections are shown in
FIG. 4. A block diagram of the Logic section 56 is shown in FIG.
5.
The Modulator section 52 accepts input synchronization and command
data from a multiplexer 58 in Logic section 56 (FIG. 5) and
modulates the carrier with this input. The Modulator 52 is
controlled by two gate signals which are generated in the Logic
section 56. These signals are labeled as the Data Transmission and
the Sync Alert Gates in FIG. 4. The Data Transmission Gate enables
a Bi-Phase Modulator 60, and the Sync Alert Gate enables a Sync
Oscillator 62. The Sync Oscillator 62 produces a low frequency
tone, for instance, 750 Hz, which is coupled to a Summing Amplifier
64. After the Sync Alert Gate, the Data Transmission Gate allows
the Bi-Phase Modulator 60 to accept input data. A carrier
frequency, for instance, 1,800 Hz, may be generated in the Logic
section 56 and coupled to the Bi-Phase Modulator 60. The input data
modulate the carrier in a synchronous manner, such that input
binary zeros and ones produce, respectively, O and .pi. radians of
phase shift on the carrier signal.
The Summing Amplifier 64 combines the modulated carrier and the low
frequency Sync Alert signal, amplifies these signals and couples
the output to an Isolation Transformer 66. The Summing Amplifier 64
produces the proper signal power and impedance levels, for
instance, for driving a voice grade telephone line or equivalent
Communication Link 22. The Isolation Transformer 66 may convert the
unbalanced output signals from the Summing Amplifier 64 to balanced
signals for transmission over the attached Communication Link
22.
The Isolation Transformer 66 also couples input response signals
from the Communication Link 22 to the Response Receiver section 54
of the Master Transceiver 16. These Signals are the response
signals from each attached Remote Terminal 24. These signals, for
instance, may be in the form of a binary, pulse amplitude modulated
(PAM) 1,800 Hz carrier. Response signals are coupled through an
analog AND gate 68 to a Response Signal Amplifier 70. AND gate 68
is enabled by the Response Gate generated in the Logic section
56.
The Response Signal Amplifier 70 provides sufficient gain to drive
a Full Wave Rectifier 72. This rectifier converts the bipolar
response carrier pulses into unipolar signals. The Full Wave
Rectifier 72 is coupled to a Comparator 74 which compares the
rectified input signal with a reference voltage which may be set at
a predetermined threshold value. The threshold value is set above
the average line noise and below the minimum expected signal level.
If an input signal to the Comparator 74 is above the threshold
procedures convert the unipolar PAM signals into a series of
constant voltage amplitude pulses. The resultant pulses are fed
into a Low Pass Filter 76 which sets the signal band width and
shapes the Comparator output. The Low Pass Filter output will cause
a delay of about one-third of a bit time for each input data bit.
Otherwise, this output represents the data bit stream as
transmitted from the Remote Terminals 24.
The remaining circuitry in the Response Receiver section 54
converts the detected response data stream into digital data
suitable for processing, for instance, by digital Computer 12, via
Interface Equipment 14. The response data stream is coupled to two
separate circuits. One circuit generates timing signals which are
utilized to decode the data, and a second circuit shapes the input
data for acceptance and storage in a Shift Register circuit.
For the first circuit, response data pulses are coupled to a first
Differentiator 78. The first initial input data pulse is
differentiated in the first Differentiator 78 and the leading edge
of this pulse is utilized to set a first Bistable circuit 80.
Immediately when first Bistable circuit 80 is set the output gate
from first Bistable circuit 80 releases a Master Response Bit Clock
circuit 82. This clock is adjusted to free run approximately at the
data bit rate, for instance, 1,200 Hz. Immediately upon release,
the Master Response Bit Clock 82 generates a bit clock pulse, for
instance, 10 to 25 microseconds in extent. These Bit Clock pulses
continue approximately at the bit rate, until first Bistable
circuit 80 is reset by means of a pulse from the Logic section
56.
The output gate from first Bistable circuit 80 also is coupled to a
second Differentiator 84. The differentiated output is utilized to
set a second Bistable circuit 86 and to reset a Response Counter 88
to zero. In the set state, second Bistable circuit 86 output
enables an AND Gate 90 such that the Response Bit Clock pulses are
coupled to the Response Counter circuit 88 and to a Bit Clock Delay
92. The Response Counter 88 accumulates six bit clock counts, which
corresponds to five complete bit time intervals, including the
first initial input data bit. At the end of the 5-bit interval and
coincident with the sixth count, the Response Counter circuit 88
generates a reset pulse to second Bistable circuit 86.
Consequently, the enable gate to AND Gate 90 is removed, and no
further Bit Clock pulses are passed. In addition, a reset pulse
from the Logic section 56 is coupled to first Bistable circuit 80
which resets this Bistable circuit. In the reset state, first
Bistable circuit 80 disables the Master Response Bit Clock 82. The
actual time of the reset pulse to first Bistable circuit 80 occurs
just prior to the minimum time possible for input of the next group
of response data bits in the next sequential response time
interval. Precise timing distinction between the reset-time of
first Bistable circuit 80 and an immediately following set-time is
augmented by the slight delay of data pulses as they occur from the
Low Pass Filter circuit 76. Thus, it will be impossible to attempt
setting of first Bistable circuit 80 at the same time that it is
being reset by the pulse from the Logic section 56. The output Bit
Clock pulses from AND Gate 90 are coupled to the Bit Clock Delay
circuit 92. In this circuit, a delay of about one-half bit time is
generated and the delayed clock pulses are coupled to a Shift
Register 94.
In the second circuit, response data pulses are coupled directly
from the Low Pass Filter 76 to a Data Shaper 96. The Data Shaper 96
shapes the response data pulses and couples them to Shift Register
94. The input Bit Clock pulses to the Shift Register 94 are
utilized to clock response data bits into the Shift Register
Circuit. For instance, the first delayed Bit Clock pulse occurs at
a time which is coincident with the time of the first data bit from
the Data Shaper 96. This coindicence enables sampling of the
response data bit pulse at the approximate midpoint, and permits
storage of the value of this response data bit in the Shift
Register 94. When five response bits have been stored in the Shift
Register 94, a pulse from Logic Section 56 can be used to cause the
Shift Register to dump its contents into a Response Storage
Register 98. Towards the end of a communication cycle, for
instance, at count 7251, the contents of the Response Storage
Register 98 may be dumped into the attached Computer facility 12.
Use of a Response Storage Register permits rapid dumping of all
response data which have been accumulated during one communication
cycle, and further enables more efficient usage of an attached,
on-line, real-time, digital computer, as illustrated at 12. The
response data bits may be utilized in the computer to generate
appropriate output commands.
A preferred embodiment of the Logic section 56 is shown in FIG. 5.
The logic circuitry may be utilized to generate all timing
information for the operations of the Central Facility 10, for
instance, timing for the communications cycle, synchronization
signals, command signals, and response signals. The Logic section
56 contains a crystal controlled oscillator 100, which, for
instance, may produce a continuous 180 kHz signal. All timing
functions can be derived from or synchronized with this clock
signal. The 180 kHz signal may be divided by 50, for example, in a
first Frequency Divider 102 to produce a 3,600 Hz clock. The 3,600
Hz clock may be divided by 2 in a second Frequency Divider 104 to
produce an 1,800 Hz clock, and by 3 in a third Frequency Divider
106 to produce a bit Clock of 1,200 Hz. Finally, the 3,600 Hz clock
may be coupled to a fourth Frequency Divider 108 which is a gating
circuit utilized with the response time interval.
A Master Counter 110 utilizes the 3,600 Hz clock input to produce a
number of output timing pulses. The total communication cycle time
may be determined, for instance, by the 7610 count output, which
resets the Master Counter 110 to zero, coincident with the 7611th
count. The 7610 count output is also utilized for reestablishing
zero phase in the first, second, and third Frequency Divider
circuits 102, 104 and 106.
The 7251 count output pulse sets a first Bistable circuit 112,
which generates, at one of its outputs, the Sync Alert Gate. This
gate is utilized in the modulator section to release the Sync
Oscillator 62. Count 7251 also resets a fourth Bistable circuit
114. In the reset state, the Fourth Bistable circuit 114 couples a
logical 1 from its Q output to an AND Gate 116. Count 7301 resets
the first Bistable circuit 112. In the reset state, the first
Bistable circuit 112 couples a logical 1 from its Q output to AND
Gate 116. These two inputs to AND Gate 116 produce the Command Data
Gate at the output of and Gate 116. The 7251 count output pulse
also is utilized in the Response Receiver section 54 to dump the
response data in Storage Register 98 into the computer facility
12.
The 0030 count output pulse sets a second Bistable circuit 118. In
the set state, the second Bistable circuit 118 generates the
control gate for use in a Sync Word Generator 120. The 0051 count
output pulse resets the second Bistable circuit 118 which removes
the control gate.
The 0051 count output pulse also sets a third Bistable circuit 122.
In the set state, the third Bistable circuit 122 generates the Data
Input Gate. The 2301 count output pulse resets the third Bistable
circuit, which terminates the Data Input Gate.
The 2301 count output pulse also sets the fourth Bistable circuit
114. In the set state, the fourth Bistable circuit 114 generates
the Response Gate at its Q output. The fourth Bistable circuit is
reset by the 7251 count output pulse, as mentioned above.
The third Frequency Divider 106 applies 1,200 Hz bit clock pulses
to the Sync Word Generator 120. The Sync Gate output from the
second Bistable circuit 118 enables the Sync Word Generator 120,
such that a fine-sync code word, for instance, 0001100, may be
produced and coupled to the Multiplexer 58.
The Multiplexer 58 accepts the sync word during the Sync Gate time
and accepts the computer generated commands during the Data Input
Gate time. The computer generated commands could also be stored
once each communication cycle in a Storage Register (not shown),
such that these commands are appropriately processed into the
Multiplexer 58 during the Data Input Gate time. Thus, the
Multiplexer 58 permits the sync word to be time division multiplied
with the data bits from the Computer 12.
The Q output of the fourth Bistable circuit 114 provides the
Response Gate, as mentioned above. The Response Gate is coupled to
the Response Receiver section 54 and enables analog AND gate 68.
The Response Gate also enables the fourth Frequency Divider 108 in
the Logic section 56. Thus, the 3,600 Hz clock is divided by 33 in
this circuitry, beginning, for instance, at count 2301 and
terminating at count 7251. The difference count between these two
counts is 4950, which, after division by 33, produces 150 Response
Time Base output pulses. These pulses occur, for instance, at 150
equally spaced intervals of time. They furnish the Response Time
Base input signals to reset the first Bistable circuit 80 and to
dump the contents of Shift Register 94 into the Response Storage
Register 98. Finally, the Response Gate from the fourth Bistable
circuit 114 output is utilized to enable AND Gate 68, such that all
response data signals from the Communication Link 22 may be coupled
to the Response Signal Amplifier 70, shown in FIG. 4.
IV. DESCRIPTION OF PREFERRED REMOTE TRANSCEIVER CIRCUITRY FOR THE
COMMUNICATION LINK SYSTEM
A Remote Transceiver 26 may comprise, for instance, a Sync Detector
124, a Data Receiver 126, a Response Modulator 128, and a Logic
section 130. Block diagrams for the first three sections are shown
in FIG. 6. A block diagram of the Logic section is shown in FIG.
7.
A Remote Transceiver 26 receives and detects coarse and fine
synchronization information, demodulates and processes a discrete
group of data signals corresponding to its own command data, and
processes, modulates, and transmits its response data to the
Central Control Facility 10. The response data may correspond to
the existent state of an attached Traffic Control Device 20, or an
attached Vehicle Detector device 30. Response data may also include
information from an Emergency Vehicle Locator 32.
Signals transmitted from the Central Control Facility 10 may be fed
to each Remote Transceiver 26 through an Isolation Transformer 132,
for instance, as shown in FIG. 6. In a remote unit, the Isolation
Transformer 132 is coupled to an Amplifier 134 for received input
signals, and it is coupled to another amplifier 136 output via a
Relay 138 for transmission of response signals to the attached
Communication line (i.e., Communication Link 22).
Discussion of the various circuit functions will follow the
sequence of events as they occur in real time. Sync detection is
the first major event preceding any given communication cycle in a
remote unit. Synchronization may be established from circuit
functions which can occur, for instance, in three sequential
events. The first event may be related to the Sync Alert signal
which can be a low frequency, for instance, a 750 Hz tone. This
signal is amplified in Amplifier 134, coupled to a Limiter 140, and
subsequently, coupled to a Differentiator 142. This low frequency
tone does not cause detrimental responses in other circuits which
are coupled to the output of Amplifier 134 or to the output of
Limiter 140.
Limiter 140 removes any amplitude variations from input signals and
produces a constant amplitude output. However, the phase of input
signals is not altered by the action of Limiter 140. For the Sync
Alert tone, the output of Limiter 140 is coupled to Differentiator
142, which produces a stream of narrow positive pulses at a rate
equal to the positive zero crossing rate of the Sync Alert tone.
These positive output pulses from Differentiator 142 are coupled to
Monostable Delay circuit 144, which delays each pulse in time by an
amount which is slightly less than the period of the Sync Alert
tone. For instance, if 750 Hz is utilized for the tone with a
period of approximately 1.3 milliseconds, the inserted delay might
be approximately 1.2 milliseconds. These delayed output pulses are
coupled to a Window Monostable circuit 146, which generates a
relatively narrow gate for each delayed input pulse. The duration
of the output of the Window Monostable 146 is adjusted such that
the generated gate or window will bracket the anticipated time of
the next sequential pulse of the Sync Alert tone from
Differentiator 142. This coincidence, if it occurs, is established
in the Correlation Gate circuitry 148, which is enabled by the
output of the Window Monostable 146. The output pulses from
Differentiator 142 also are input to the Correlation Gate 148.
Therefore, if the proper rate of pulses occurs, these pulses will
pass the Correlation Gate 148 and be coupled to the Sync Arm
Detector 150. It should be noted that, if the pulses which are
input to Monostable Delay 144 occur at a higher rate than that
anticipated for the Sync Alert tone, Monostable Delay 144 will
block, and no output pulses are coupled to the Window Monostable
circuit 146.
The Sync Arm Detector 150 examines the input pulse rate from the
Correlation Gate circuitry 148. An output to Monostable Delay 152
is produced only if a specified number of pulses are accumulated in
the Sync Arm Detector 150 within a predetermined time interval.
When an output is produced from the Sync Arm Detector 150,
Monostable Delay 152 is initiated. This circuitry is adjusted to
generate a delayed output pulse immediately prior to the
anticipated time for occurrence of the Fine Sync word. For the
circuitry described herein, a delay of approximately 93
milliseconds is adequate. The output of Monostable Delay 152
initiates a Sync Window Monostable 154 which outputs a Fine-Sync
Window Gate. The extent of this gate may be approximately 10
milliseconds. The output of Sync Window Monostable 154 is coupled
to AND Gates 156, 158 and 206, and is utilized to enable these
gates.
The second event in the synchronization interval may be related to
the establishment of a stable carrier reference. Immediately
following the Sync Alert tone, a burst of unmodulated carrier may
be transmitted from the Central Facility 10. For instance, 1,800 Hz
may be utilized as a satisfactory carrier frequency. The burst of
unmodulated carrier may be received and amplified in Amplifier 134
and coupled to a Frequency Multiplier 160. These carrier signals do
not cause detrimental responses in other circuits which are coupled
to the output of Amplifier 134. The Frequency Multiplier 160
produces full wave rectification of the input carrier and generates
second harmonics of the carrier. The rectified output is amplified
in an Amplifier 162 and coupled to a Band Pass Filter 164. If an
1,800 Hz carrier frequency is utilized, this filter may be designed
to suppress frequencies other than the second harmonic frequency of
3,600 Hz. This second harmonic signal is utilized to obtain and
maintain a stable reference for demodulation of data from the
carrier. The output of Band Pass Filter 164 is limited in a Limiter
166 and subsequently coupled to a Phase Detector 168. Phase
Detector 168, a Low Pass Filter 170, and a Voltage Controlled
Oscillator 172 comprise a phase-lock-loop circuit. Phase Detector
168 compares the phase of the input second harmonic of the carrier
with the phase of the output from the Voltage Controlled Oscillator
172. Any difference in phase is detected as the loop phase-error
and is filtered by Low Pass Filter 170. This filtered phase-error
is utilized to correct the phase of the Voltage Controlled
Oscillator 172, which ultimately maintains an output signal in
phase quadrature with the input second harmonic of the carrier. The
output of the Voltage Controlled Oscillator 172 also is coupled to
a Frequency Divider 174 via a Phase Shifter 176. The Frequency
Divider 174 halves the input frequency, thus regenerating the
carrier frequency. Therefore, a stable carrier reference signal is
generated, which may be utilized as the reference phase for a Phase
Detector 178. Phase Detector 178 functions as the phase detector of
the modulated carrier for all input data signals. It should be
noted that the carrier phase reference which has been generated
will be either in phase (0.degree.) with the real input carrier or
out of phase (180.degree.) with the real input carrier. This
circumstance is a result of the second harmonic generation in the
Frequency Multiplier 160. This phase ambiguity will be determined
subsequently by the Fine-Sync Detection circuit.
The third event in the synchronization interval may be related to
Fine-Sync detection. Immediately following the burst of unmodulated
carrier, a Fine-Sync word may be transmitted from the Central
Facility 10. For instance, the word may comprise a 7-bit code word
such as 0001100. This code word may be received and amplified in
Amplifier 134, coupled to Limiter 140, and subsequently coupled to
Phase Detector 178. The code word does not cause detrimental
responses in other circuits. Phase Detector 178 compares the phase
of the input modulated carrier with the reference carrier phase.
The output of Phase Detector 178 comprises signals which correspond
to phase modulation of the input carrier, which, in the present
instance, correspond to the binary zeros and ones of the 7-bit code
word. The output of Phase Detector 178 is coupled through a Low
Pass Filter 180 to a Data Shaper 182. Corresponding to the input
signals, the Data Shaper 182 generates a binary, unipolar wave
output. This output comprises an estimate of the transmitted data
stream. The output of Data Shaper 182 is coupled to a
Differentiator 184 and to a 4-bit Shift Register 186.
The output of Differentiator 184 is coupled to a Full Wave
Rectifier 188. The resultant output of this rectifier comprises a
stream of positive pulses which occur at the transitions of the
input data stream. For instance, for the input Sync word 0001100,
the output pulses from the Full Wave Rectifier 188 will occur at
the beginning of the fourth bit and at the beginning of the sixth
bit. If the Sync word occurs at the prescribed time, AND Gate 156
will be enabled and will couple the first one of these Full Wave
Rectifier output pulses to an AND Gate 190. In addition, the output
of the Sync Window Monostable 154 is coupled to a Bistable 192
which sets this Bistable when the Sync Gate is present. In the set
state, the output of Bistable 192 output enables AND Gate 190.
Therefore, the first output pulse from the Full Wave Rectifier 188
is coupled through AND Gate 190 back to Bistable 192 and resets
this bistable element. Consequently, AND Gate 190 is disabled, and
the second pulse from the Full Wave Rectifier 188 is not coupled
through AND Gate 190. The actions of the two AND Gates, 156 and
190, serve to detect the initial time of occurrence of the last
four bits in the 7-bit Fine-Sync code word.
The output of Bistable 192 is also coupled to a Remote Bit clock
194 and a Shift Monostable 196. While in the set state the output
of Bistable 192 gates off the Remote Bit Clock 194. However, at the
transition time which occurs at the beginning of the fourth bit in
the code word, Bistable 192 is reset. At this time, the output of
Bistable 192 gates on the Remote Bit Clock 194, whose output signal
is coupled to the 4-Bit Shift Register 186. Simultaneously, the
Shift Monostable 196 is initiated from the output of Bistable 192.
The output of Shift Monostable 196 enables the 4-Bit Shift Register
186 and permits the remaining four bits of the code word to be
clocked into the 4-Bit Shift Register 186. These four bits consist
of the two logical ones followed by the two logical zeros, which
are coupled to the 4-Bit Shift Register 186 from the output of Data
Shaper 182.
The input four bits to the 4-Bit Shift Register 186 are compared
with a stored Sync word. The logic circuitry utilized in this
comparison consists of a set of four Inverters, 198, 200, 202 and
204 and AND Gates 206 and 158. AND Gates 206 and 158 are enabled by
the output of the Sync Window Monostable 154. When the contents of
4-Bit Shift Register 186 compare on a bit by bit basis with the
stored code word, a pulse is output through AND Gate 206. This
output pulse represents the fact that Fine-Sync has been detected
and time T.sub.0 is established. The output pulse also represents
the fact that the proper data sense has been detected in that the
correct 0.degree. phase relationship exists for the reference
carrier to Phase Detector 178. On the other hand, when the contents
of 4-Bit Shift Register 186 compare on a bit by bit basis with the
logical compliment of the stored code word, a pulse is output
through AND Gate 158. This output pulse also represents the fact
that Fine-Sync has been detected, and the time T.sub.0 is
established. However, this output pulse represents the fact that an
opposite data sense has been detected in that a 180.degree. phase
relationship exists for the reference carrier to Phase Detector
178.
The outputs of AND Gates 206 and 158 are both coupled to an OR Gate
208. Thus, the output of OR Gate 208 represents Fine-Sync detection
and establishes T.sub.0. The output of OR Gate 208 is coupled to
the Logic section 130 and is utilzed for resetting a Remote Master
Counter 210 (FIG. 7). OR Gate 208 is also coupled to a Frequency
Divider 212. This circuit divides the output of a Remote
Crystal-controlled 180 kHz Clock 214 by 150, and produces the
Remote Bit Clock rate at 1,200 Hz. The input to Frequency Divider
212 from OR Gate 208 reestablishes the correct phase of the Remote
Bit Clock pulses once each communication cycle. These pulses are
coupled to the Logic section 130 as Remote Bit Clock pulses.
The output of the Frequency Divider 212 is also coupled to and
synchronizes an 1,800 Hz Carrier Oscillator 213. The output of
Carrier Oscillator 213 is coupled to a Response Modulator 226. The
Response Modulator 226 produces Pulse Amplitude Modulation of the
carrier input according to the binary input response data stream.
The modulated carrier output is amplified in Amplifier 136. The
impedence of the output of Amplifier 136 is adjusted appropriately
for transmission of the modulated carrier through the Relay 138 and
through the Isolation Transformer 132 to the attached communication
line.
The outputs of AND Gates 206 and 158 are coupled separately to a
Bistable 216. If there is a pulse from AND Gate 206, Bistable 216
is set. If there is a pulse from AND Gate 158, Bistable 216 is
reset. In the set state, the Q output of Bistable 216 enables an
AND Gate 218 and the data stream from the Data Shaper 182 is
coupled directly to an OR Gate 220. In the reset state, the output
Q of Bistable 216 enables an AND Gate 222, and the data stream from
the Data Shaper 182 is inverted in an Inverter 224 before being
coupled through AND Gate 222 to OR Gate 220. Therefore, Bistable
216, AND Gates 222 and 218, and Inverter 224 function such that the
correct, positive data sense for the data bit stream is always
coupled to OR gate 220. The data stream from OR Gate 220 is coupled
to the Logic section 130 for further processing.
Coarse and Fine Synchronization have been detected and a stable
carrier reference for subsequent command data demodulation has been
established. An example of remote Logic Circuitry 130 is shown in
block form in FIG. 7. The Logic section 130 demultiplexes the
appropriate input command data which correspond uniquely to each
particular Remote Transceiver 26. Subsequently, these data may be
processed and utilized for remote control of an attached Traffic
Control Device 20. The Logic section 130 also multiplexes response
signals into a predetermined time interval and couples this
information to the Response Modulator 226 (FIG. 6). A response
signal may correspond to the existent state of an attached Traffic
Control Device 20, or Vehicle Detector 30, or an emergency Vehicle
Locator 32.
The output Sync pulse from OR Gate 208 in the Data Receiver Section
126 of FIG. 6 is coupled through a Reset Pulse Shaper 228 to the
Remote Master Counter 210 as shown in FIG. 7. This pulse resets the
Remote Master Counter 210 to zero, corresponding to time T.sub.0.
The output Bit Clock pulses from the Data Receiver section are
coupled through a Bit Clock Pulse Shaper 230 to the Remote Master
Counter 210. These Bit Clock pulses are also coupled to a Clock
Pulse Delay circuit 232 and to a Data Sample Pulse Generator
234.
For the circuitry of the preferred embodiment under discussion,
each Remote Terminal 24 is assigned a partcular time interval for
reception of command data. The beginning of this time interval for
any given Remote Terminal may be designated, for instance, as X
counts after T.sub.0. In addition, each set of commands to each
remote unit may be comprised, for instance, of two, three, four, or
five bits. The particular number of bits, n, contained in a command
to a given Remote Terminal 24 depends on the required number of
different functions which the given Remote Terminal must perform.
For instance, in a received command, the first bit may be utilized
to designate the Remote or Local Control Mode, being a binary one
for Remote Control or a binary zero for Local Control. The
remaining one, two, three, or four bits in the command to a given
Remote Terminal can be utilized, respectively, to describe two,
four, eight, or 16 different commands.
The Remote Master Counter 210 outputs a pulse at X counts and sets
a Bistable 236. In the set state, Bistable 236 enables a Command
Decode Counter 238. The input Bit Clock pulses also are coupled to
the Clock Pulse Delay circuit 232 which delays input Bit Clock
pulses by a small amount of time, for instance, 10 microseconds.
This delay enables the same count X to be counted as the first
count in the Command Decode Counter 238. When enabled by the output
of Bistable 236, the Command Decode Counter 238 counts the delayed
input clock pulses. At the time of the delayed first input clock
pulse to the Command Decode Counter 238, an output gate is
generated by the Command Decode Counter circuit and is coupled
separately to an AND Gate 240. This output gate is approximately
one bit time in extent and is labeled as Count 1 into AND Gate 240
in FIG. 7. Subsequently, when the next bit clock pulse is input to
the Command Decode Counter 238, corresponding to n = 2, the
previously output gate to AND Gate 240 is terminated, and another
similar gate is separately coupled to an AND Gate 242. This
procedure is repeated up to and including tne nth gate to AND Gate
n. These gates are enabling gates for the respective AND Gates 240
through n. If a given remote unit requires 5 bits in its command,
then n = 5, and there will exist five AND Gates.
The Command Decode Counter 238 also accumulates counts to the n + 1
count, at which time a pulse is coupled to and resets Bistable 236.
As Bistable 236 is reset, the output thereof resets the Command
Decode Counter 238 to zero and disables the circuit.
The clock pulses from the Bit Clock Pulse Shaper 230 are also
coupled to the Data Sample Pulse Generator 234 which delays each
clock pulse by approximately one-half bit time and couples the
pulses in parallel to AND Gates 240 through n. Therefore, AND Gate
240, when it is enabled, couples the corresponding delayed pulse
from the Data Sample Pulse Generator 234 to a Bistable Latch
circuit 244. Subsequently, AND gate 242, when it is enabled,
couples the correspondingly delayed pulse from the Data Sample
Pulse Generator 234 to Bistable Latch circuit 246, etc. These input
pulses to Bistable Latches 244 through n are utilized to enable the
latches. Each latch circuit is enabled sequentially for
approximately one-half bit time.
The detected data stream from OR gate 220 in the Data Receiver
section is coupled in parallel to the Bistable Latches 244 through
n. Therefore, during the enabled interval of each latch, the
respective latch will assume the state of the input data bit which
exists in the data stream at that particular time. In this manner,
the serial stream of data bits is converted to a parallel digital
word for use as a command, for instance, to an attached Traffic
Control Device 20. The Bistable Latches 244 through n may be
connected separately to Interface Equipment 28 for actual control
of on-the-street traffic lamp indicators or Traffic Control Devices
20.
The response time interval for any given remote unit can be
determined, for example, in the following manner. At the Central
Facility 10, the total response time for all attached remote units
on a single communication line may be designated as the interval
from count 2301 to count 7251, as shown previously in FIG. 2. This
count difference is 4,950 counts. This count interval may be
divided, for instance, into 150 equal and discrete response time
intervals. Therefore, each discrete interval would be 33 counts in
extent, representing approximately 9.2 milliseconds in time, based
on the 3,600 Hz count rate at the Central Facility 10. These
procedures permit a total of 150 remote units to be coupled to one
communication line.
The particular discrete response time interval of 9.2 milliseconds
permits each Remote Transceiver 26 to transmit a response signal
with a maximum bit length of five bits. Therefore, for an assumed
bit rate of 1,200 Hz, a maximum length response signal occupies
about 4.2 milliseconds in time. This provides about 5 milliseconds
of additional time for transmission delays to and from any remote
unit. A maximum one-way transmission delay of 2.5 milliseconds
corresponds to a 25 mile distance at an assumed 10.sup.4
miles/second communication line transmission speed. Other
procedures could be utilized to increase the total number of
attached remote units. For instance, the bit rate could be
increased. On the other hand, particular compensation for
transmission delays could be applied, such that the discrete
response time intervals could be decreased. However, in the
circuitry of the preferred embodiment, the simplest procedures have
been followed to facilitate description of the basic concepts of
the invention in the clearest possible manner. This has also been
done in order to allow maximum flexibility for the insertion or
changing of any remote unit and in order to permit installations to
be made at any arbitrary distance from the Central Facility 10.
In FIG. 2, command data from the Central Facility 10 are initiated
at count 51, which would be equivalent to T.sub.0 in a Remote
Transceiver which experienced zero transmission delay time.
However, a maximum one-way transmission delay of 2.5 milliseconds
is assumed for each Remote Transceiver. Consequently, the observed
T.sub.0 time in any given Remote Transceiver is assumed to have
been delayed by 2.5 milliseconds. Since the response time in any
given Remote Transceiver is determined by counting a given number
of counts after T.sub.0, the initiation of this response time in a
Remote Transceiver must also be assumed to have been delayed 2.5
milliseconds. Therefore, the actual response time interval
available at any given Remote Transceiver is approximately 6.7
milliseconds, which is obtained by subtraction of 2.5 milliseconds
from the total discrete time interval of 9.2 milliseconds.
In any given Remote Transceiver, if the response signal
transmission is initiated at Y counts after T.sub.0, there will
remain 6.7 milliseconds for transmission of the particular response
signal back to the Central Facility 10. If a maximum bit response
signal of five bits is assumed for each remote unit, this five bit
response signal will require about 4.2 milliseconds at a bit rate
of 1,200 Hz. Thus, there will remain about 2.5 milliseconds for
transmission of this particular response signal back to the Central
Facility 10, before another response signal from some other Remote
Terminal is to be received at the Central Facility.
The initiation of the particular response interval allotted to any
given remote unit is actually determined by the Y-1 count output
from the Remote Master Counter 210, instead of the Y count. This
procedure allows adequate time for transmission circuitry
stabilization, prior to actual transmission of the response
signals.
In FIG. 7, the Y-1 count output from the Remote Master Counter 210
is coupled to and sets a Bistable 248. When in the set state,
Bistable 248 enables a Response Counter 250. The output of Bistable
248 is also coupled to the transmission Relay circuit 138, shown in
FIG. 6, which permits coupling of the Amplifier 136 through the
Isolation Transformer 132 to the Communication line, which may be
Communication Link 22, for example.
The function of the Response Counter 250 is analogous to that
described above for the Command Decode Counter 238. When enabled
from Bistable 248, the Response Counter 250 accepts delayed Bit
Clock pulses from the Clock Pulse Delay circuit 232 and outputs
corresponding and separate gates which are 1 bit time in extent. It
is noted that the first output gate occurs at the time of the
second input bit clock pulse to the Response Counter 250. This gate
is coupled separately to a Response AND Gate 252 and is labeled as
Count 2. Subsequently, the third input clock pulse to the Response
Counter 250 initiates generation of the second gate which is
coupled separately to a Response AND gate 254. The n + 1 clock
pulse initiates generation of the nth gate in the Response Counter
250, and this gate is separately coupled to Response AND Gate n. If
five bits are required in the command signal to a given remote
unit, the response signal must also contain five bits, and there
would thus exist five Response AND Gates in the response
circuitry.
Each of the gate outputs from the Response Counter 250 are enabling
gates. Since these gates occur sequentially, each Response AND Gate
is enabled in a sequential manner. The response signal data are
also coupled separately to the Response AND Gates. These data are
in binary form. At any given time, each response data bit to each
Response AND Gate will be a binary zero or one, dependent on the
particular response signal to be transmitted back to the Central
Facility 10. The first binary bit input to Response AND Gate 252
will be coupled to OR Gate 256 when Response AND Gate 252 is
enabled. Similarly, the remaining data bits are serially coupled to
OR Gate 256. Therefore, the output of OR Gate 256 is a serial data
stream representing the response signal to be transmitted.
As mentioned previously, the response data signals may be
representative of the existent state of attached Traffic Control
Devices 20, Vehicle Detectors 30, or Emergency Vehicle Locators 32.
All of the above response signals may be present at a particular
Remote Terminal. In such a case, three Remote Transceiver units 26
could be untilized, one for each type of response signal. On the
other hand, circuit modifications could be implemented in a Remote
Transceiver 26 such that the discrete time interval allotted could
be expanded to include the additional types of response signals.
These response signals are discussed further hereinafter.
V. DESCRIPTION OF THE PREFERRED INTERFACE EQUIPMENT
FOR COMMAND EXECUTION FOR THE COMMUNICATION LINK
SYSTEM
A variety of interface equipment could be utilized for coupling the
Computer 12 to the Master Transceiver 16 and for coupling local
Traffic Control Devices 20 to Remote Transceivers 26. With respect
to coupling information to and from a digital computer, the use of
input and output storage registers for binary data is the simplest
method. Thus, response data from all Remote Transceivers 26 may be
accumulated in an output storage register contained, for instance,
in Interface Equipment 14. This register may be dumped once each
communication cycle into an input port or channel of the digital
computer facility. In a similar manner, output commands generated
by the computer software package can be dumped once each
communication cycle into an input storage register contained, for
instance, in Interface Equipment 14, for subsequent readout by the
Multiplexer 58 in the Logic section 56 of the Master Transceiver
16. These procedures will enable the attached on-line, real-time
computer facility to be utilized in an efficient manner. For
instance, in a time-sharing computer facility, many other
functions, calculations, etc. can be maintained, together with the
Traffic Transporation Control Function.
For Interface Equipment 28 which might be coupled to a Remote
Transceiver 26, preferred circuitry will be described which is
simple in function and relatively inexpensive in cost. There are a
number of different types of electromechanical and solid state
devices which may be utilized for the local control of traffic lamp
indicators at any given street intersection. Such devices are
called local Controllers. Thus, a Local Controller is a device
which energizes different traffic lamp indicators at a street
intersection according to some prearranged input program. An input
program may consist of appropriate input signals from some master
controller facility, or the input signals may be internally
generated with in the Local Controller circuitry. In some cases,
these input programs may be altered to some extent by auxiliary
inputs from nearby Vehicle Detectors 30.
For the simplest configuration of the disclosed System, a Local
Controller device is assumed operative at each intersection for
which a remote control function is desired. Transfer of commands to
appropriate lamp circuits can be accomplished by simple interface
equipment between the Remote Transceiver 26 and the Local
Controller device. A complex intersection problem of three
through-streets will be assumed, and example circuitry will be
discussed which is applicable to such an intersection. More simple
intersection problems can be treated with more simple interface
circuitry, as will be discussed subsequently.
In general, a six street intersection (three through-streets) will
require 5-bit commands to satisfy all necessary traffic functions.
The commands may be stored once each communication cycle in five
Bistable Latches, 244, 246, n-2, n-1, n as previously discussed in
reference to FIG. 7. The outputs of these Bistable Latches may be
coupled separately to five Bistable circuits 258, 260, n-21, n as
shown in FIG. 8. The Bistable outputs may be coupled to a Logic
circuit 262, which can be utilized to specify the mode of control
for the attached Local Controller, either Remote or Local control.
The outputs of Bistables 260 through n represent a particular input
command at any given time, and these outputs may be coupled
separately to a Logic circuit 264.
As an example, Logic circuit 262 may comprise circuit functions as
shown in FIG. 9. An input voltage to Bistable 258 represents a
binary one for the first bit in a command and further represents a
Response Monitor function. That is, if all command bits to
Bistables 260 through n have zero values, Logic 262 circuitry will
not change the attached Local Controller from the Local Control
Mode. However, appropriate data representing the existent states of
the traffic lamp indicators will be transmitted back to the Central
facility 10. Therefore, the Local Controller functions can be
remotely monitored. These response signals will be discussed
subsequently in relation to FIG. 14.
The output of Bistable 258 is coupled to AND gate 270. The outputs
of Bistables 260 and n-2 are coupled to OR gate 271. The outputs of
Bistables n-1 and n are coupled to OR gate 273. The outputs of OR
gates 271 and 273 are coupled to OR gate 274. The output of OR gate
274 is coupled to and utilized as an enabling gate for AND gate
270. Therefore, when there is an output from Bistable 258 to AND
gate 270, and when at least one command bit is present from any one
of Bistables 260 through n, AND gate 270 will be enabled. The
output of AND gate 270 is coupled to AND gate 266. An enabling gate
to AND gate 266 may be provided from any particular traffic lamp
indicator circuit desired. For the present discussion, it is
assumed that the local Control Mode can be interrupted at the Amber
phase of the No. 1 street. Therefore, a portion of the AC power to
the No. 1 Amber lights 272 may be coupled over line 281 to Diode
279. The half wave rectified output of Diode 279 may be used as an
enabling gate to AND gate 266.
The output of AND gate 266 is coupled to and sets Bistable 276. In
the set state, Bistable 276 output activates Relay 268. AC power
for sequencing or stepping of the different phases of the attached
Local Controller is removed by means of Relay contacts 280 and
transferred to line 282. Line 282 then couples AC power for the
traffic lamp indicator circuits for the Remote Control Mode.
At any subsequent time, if all command bit values are made zero,
the output of OR gate 274 will be eliminated. The output of OR gate
274 is also coupled to Flip Flop 277. This Flip Flop 277 can be
arranged such that, with zero input, an output pulse may be coupled
to Diode 285 and to Delay Monostable 278. The output of Diode 285
is coupled via line 283 to the Amber line inputs No. 1, No. 2, and
No. 3. This output from Diode 285 will cause the appropriate Amber
lamps to be illuminated, as will be described subsequently. Delay
Monostable 278 may be adjusted to output a delayed pulse to reset
Bistable 276. In the reset state, Bistable 276 output releases
Relay 268, and the Local Control Mode is reestablished. An
appropriate delay time for Delay Monostable 278 would be 4 or 5
seconds.
Logic circuitry 262 permits a safe and appropriate change from any
traffic signal phase under the Remote Control Mode back to the
original Amber phase of the Local Control Mode.
Logic circuit 264 indicated in FIG. 8 may comprise a 4-input to
16-output Decoder Logic circuit, similar to those commercially
available. Such a logic circuit accepts binary data, a zero or one
bit input on four separate channels. Dependent on the particular
set of input data, one unique output line, out of a possible 16
lines, will be activated. Simple circuitry comprising diodes and
resistors also can be utilized to accomplish the same function as
logic circuit 264.
In an electromechanical type Controller, there exists a series of
motor-driven cams which independently operate a series of cam
switches which, in turn, apply AC power to particular lamp
indicators under the local Control Mode. If the locally controlled
traffic cycle is interrupted when the Amber lamps 272 for the first
Street are illuminated, the associated cam switches for this type
of Local Controller are closed for this No. 1 Amber circuit. In
addition, the Red Lamp indicators for a second and third Streets
will be illuminated, and the associated cam switches will be
closed. All other cam switches will be open at this time, except
perhaps any associated pedestrian DON'T WALK signals. It is noted
that some municipalities may require that the Green lamp indicators
remain illuminated when the associated Amber lamp indicators are
illuminated. This latter circumstance has not been assumed in the
particular circuitry described herein. However, simple circuit
changes can be made to permit the Green lamp indicators to remain
illuminated when the associated Amber light indicators are
illuminated, and will be discussed subsequently.
Other types of Local Controllers such as devices constructed from
solid state components may not utilize cam operated lamp switches.
However, there will exist a sequencing function which can be
interrupted similar to that discussed for Relay 268 in FIG. 9. Also
at any given time of interrupt, there will be some lines to traffic
lamp circuits which will have AC power applied and other lines to
traffic lamp circuits which will not have AC power applied.
Therefore, for such Local Controller types, the following circuit
discussions will be applicable.
An Example circuit for remote control of a six-street intersection
is shown in FIG. 10. The total circuit will not be described in
detail since the traffic control functions are similar for the
different streets. In addition, it is noted that many other traffic
control functions might be included by appropriate changes or
additions to the circuitry shown. For the circuitry shown in FIG.
10, there are 13 different input commands which have been
considered. For each of the three through-streets, these commands
are represented as Green, Left Turn Green, Amber, and Emergency. In
addition, a DON'T WALK Interrupt Command is included to enable
appropriate DON'T WALK signals prior to initiation of any Amber
signal. This function is included so that any pedestrian traffic
may have ample time for street clearance, before a subsequent Green
or Left Turn Green Command is issued. Also, in FIG. 10, the cam
Operated Switches mentioned previously have been indicated
symbolically. For interruption of the locally controlled function
at the time of illumination of No. 1 Amber lights, a line 284,
which comprises all currently active lamp circuits, will have AC
power always applied from the attached Local Controller in the
Remote Control Mode. A Line 286, which comprises all currently
inactive lamp circuits, will not have any AC power applied from the
associated cam switches.
In FIG. 10, there is indicated to be a relay circuit attached to
each separate type of lamp indicator, dependent on the desired
functions. For instance, for street No. 1, Left Turn Green Signals
are assumed to be desired for both street directions. Consequently,
both Red lamps for both directions will remain illuminated
throughout the illumination time of these Left Turn Green signals
and the corresponding Green lmaps for both directions of this
street will not be illuminated. For instance, for Street No. 2, a
Left Turn Green signal is assumed only for direction 1 of this
street. For street No. 3, a Left Turn Green signal is assumed only
for direction 2 of this street. Right turn indicators could be
added as they are required, since such functions are usually
coincident with the appropriate Left Turn Green signals. The
circuitry also may be adapted to permit Left Turn or Right Turn
Green signals at the beginning of the associated Green cycle time
or at the end of the associated Green cycle time.
Also indicated in FIG. 10 are 21 Response Boxes 288 through 328.
These Response Boxes simply represent the individual outputs from
the associated lamp circuits. These will be discussed subsequently
when the response interface equipment is described.
As is indicated in FIG. 10, the main AC power from Logic circuit
262 is coupled via line 282, through the contacts 330 of a Relay
446 to a line 332. AC power is input to a line 334 only if No. 1
Green is not active. Therefore, No. 2 or No. 3 Green, including
their respective Left Turn Greens cannot be activated if No. 1
Green is active. In addition, AC power is supplied to a line 336
only if both No. 1 Green and No. 2 Green are inactive.
As an illustration of the circuit functions shown in FIG. 10, a
lamp indicator cycle for Street No. 2 will be discussed. The lamp
indicator cycles for Streets No. 1 and No. 3 are similar or
identical. The pertinent elements for Street No. 2 lamp indicators
are shown in FIG. 1 for a normal traffic control cycle of this
street. When the locally controlled traffic function is interrupted
for Remote Control, Street No. 1 Amber lights 272 are illuminated,
and R lamp indicators 374 and 372 for Street No. 2 are illuminated
as depicted in FIG. 11. Since No. 1 Amber lights 272 are
illuminated, the initial input command from the Central Facility 10
will be the No. 1 Amber Command. Initiation of this command will
not cause any circuit responses, since the No. 1 Amber lamps are
initially illuminated. When the Amber lights are illuminated for a
particular street, a portion of their AC voltage is rectified and
coupled separately to flip-flop circuits for the remaining streets.
in FIG. 11, a portion of the No. 1 Amber light 272 AC voltage is
rectified in a group of diodes 342 and coupled to flip-flop
circuits 344 and 346 on a line 348 for Street No. 2, and to
flip-flop 350 and 352 on a line 347 for Street No. 3. These
rectified AC voltages activate the respective flip-flop circuits
which output enabling gates to the attached AND Gates. In addition,
the flip-flops may be arranged such that their output enabling
gates will persist for a few milliseconds after the input rectified
AC voltage is removed.
In FIG. 11, flip-flops 344 and 346 are activated from the No. 1
Amber lamp circuit and AND gates 356 and 358 are enabled.
Therefore, either a No. 2 Green or a No. 2 left Turn Green Command
could be applied to Street No. 2. A similar situation exists for
Street No. 3. For discussion purposes, it is assumed that the No. 2
Left Turn Green command is applied subsequent to removal of the
initial No. 1 Amber Command. If a positive voltage is utilized to
activate the No. 1 Amber Line, when the No. 1 Amber Command is
terminated, this positive voltage will be removed. The resultant
differentiated negative pulse can be coupled from the No. 1 Amber
Line to a Bistable 360 and used to set the Bistable. In the set
state, Bistable 360 activates a Relay 362 and AC power from line
284 is removed from the No. 1 Amber lights. The differentiated
negative pulse input to Bistable 360 is also coupled to a Bistable
364, and sets this Bistable. In the set state, Bistable 364
activates a Relay 366 and couples AC power to the R lamp indicators
338 and 340 for Street No. 1.
At the same time that the No. 1 Amber Command is terminated, the
No. 2 Left Turn Command occurs, and the No. 2 Left Turn Green line
is energized. Since AND Gate 358 remains enabled for a short period
of time, the positive voltage on No. 2 Left Turn Green line is
coupled to and sets a Bistable 368. In the set state, Bistable 368
activates a Relay 370 and applies AC power through one set of
contacts of Relay 370 to an R lamp indicator 372 for direction 2 of
Street No. 2. It is noted that both R lamp indicators for Street
No. 2, 372 and 374, are currently illuminated through contacts of a
Relay 376 to line 284. This additional coupling of AC power to the
R. lamp indicator 372 for Street No. 2 will prevent possible
blinking of this lamp indicator as execution of the No. 2 Left Turn
Green Command is completed.
When Relay 370 is activated, a portion of the AC voltage from one
of the Relay 370 contacts is rectified by a diode 378 and coupled
to a Bistable 380. This voltage sets Bistable 380 and activates
Relay 382. Through the contacts of this relay, AC power is coupled
to a G lamp indicator 384 for Street No. 2. AC power also is
coupled from the other contacts of Relay 382 through one set of
contacts of Relay 370 to an LG lamp indicator 386 for Street No 2.
In addition, the input to Bistable 380 from Diode 378 is coupled to
a Bistable 388 and through a diode to a Bistable 420. This applied
voltage sets Bistable 388. In the set state, Bistable 388 activates
Relay 376 and AC power from line 284 is removed to the R lamp
indicator 374 for Street No. 2. The R lamp indicator 372 remains
illuminated as discussed in the previous paragraph. The applied
voltage through the diode to Bistable 420 resets this Bistable. In
the reset state, Relay 428 is released and the DON'T WALK lamp
circuit for No. 2 street is activated, if these signals are present
at the intersection. A pair of R lamp indicators 390 and 392 for
Street No. 3 remain illuminated, as was their initial state, from
AC power coupled from line 284 and the associated relay as shown in
FIG. 10. Thus, No. 2 Left Turn Green Command has been executed. The
R lamp indicators for Streets No. 1 and No. 3, 338,340,390, and 392
are illuminated, and LG 386, G 384, and R 372, lamp indicators for
Street No. 2 are illuminated. This circumstance will persist until
the No, 2 Left Turn Green Command is removed.
When No. 2 Left Turn Green Command is terminated, the positive
voltage on the No. 2 Left Turn Green line is removed. The resultant
differentiated negative pulse on this line is coupled to and resets
Bistable 368. In the reset state, Bistable 368 releases Relay 370
and AC power is transferred from LG lamp indicator 386 to G lamp
indicator 394 for Street No. 2. AC power is also removed from R
lamp indicator 372 for Street No. 2. The next sequential command is
No. 2 Green Command. In this instance, the No. 2 Street G lamp
indicator 384 and a G lamp indicator 394 are already illuminated.
If the No. 2 Left Turn Green Command had been skipped, activation
of the No. 2 Green line would have coupled a positive voltage
through AND Gate 356 to Bistables 380, 388 and 420. The coupling
through AND Gate 356 would have been permitted since flip-flop 344
would have been activated from the previous Amber lamp illumination
from either Streets No. 1 or No. 3. In the present instance,
activation of the No. 2 Green line, which occurs as a consequence
of detection and processing of the No. 2 Green Command in Logic
264, FIG. 8, does not cause any other circuit response. When the G
lamp indicator 394 is illuminated, AC voltage in the form of
positive pulses are coupled through a diode 396 to a Flip-Flop 398.
Thus, Flip-Flop 398 is activated and enables an AND Gate 400 for
subsequent usage. For instance, when No. 2 Green Command is
terminated, positive voltage is removed from the No. 2 Green line.
The resultant differentiated negative pulse from differentiator 357
is coupled and resets Bistable 380. In the reset state, Bistable
380 releases Relay 382, and AC power is removed from the G lamp
indicators 384 and 394 for Street No. 2.
The next sequential command is No. 2 Amber Command. When this
command is detected and processed in logic 264, FIG. 8, a positive
voltage may be applied to the No. 2 Amber line. This positive
voltage is coupled through the enabled AND Gate 400 to a Bistable
402. Bistable 402 is set and in this state activates a Relay 404,
which couples AC power to No. 2 Amber lamp indicators. When No. 2
Amber signals are illuminated, AC voltage in the form of positive
pulses is coupled through a pair of diodes 406 to a pair of lines
347 and 349. Line 349 separately couples to a Flip-Flop 412 and a
Flip-Flop 414 for Street No. 1, and line 347 separately couples to
Flip-Flop 350 and Flip-Flop 352 for Street No. 3. Therefore, at the
termination of No. 2 Amber Command, either Street No. 1 traffic
control functions may be initiated, or Street No. 3 traffic control
functions may be initiated.
If DON'T WALK signals are utilized at an intersection, these
signals are usually activated prior to the initiation of any given
Amber lamp time. This is done so that the intersection may be
cleared of any pedestrian traffic, prior to the issuance of a
subsequent command. In addition, it is noted that no two commands
can be present on the input lines at the same time. Therefore, if a
DON'T WALK Interrupt Command is issued, the currently active line
containing a Green Command must be terminated. However, continued
illumination of the particular activated Green lamps must be
maintained. This may be accomplished by eliminating the
differentiator circuits 411, 357 and 477 attached to each Green
Command input line. Therefore, when any particular Green Command is
terminated the Corresponding G lamp indicators will remain
illuminated. Subsequently, when the associated Amber Command is
initiated, one of two situations can be implemented. If it is
desired that the presently active G lamps remain illuminated
throughout the associated Amber lamp time, then the connections
indicated by the dashed lines 408, FIGS. 10 and 11, can be made.
These lines 408, couple the differentiated pulses from the input
Amber lines to the reset terminals of the associated Green Command
Bistables. Therefore, a particular activated G lamp circuit will
not be de-activated until the subsequent and associated Amber
Command is terminated. On the other hand, if it is desired to
terminate illumination of the G lamp indicators when the associated
Amber Command is initiated, the connections indicated by the dashed
lines 410, FIGS. 10 and 11 can be made. These lines, 410 couple a
portion of the rectified AC voltage of the illuminated Amber lamps
to the reset terminal of the associated Green Command
Bistables.
The DON'T WALK signal function can be accomplished in the following
manner. The DON'T WALK Interrupt Command line is coupled directly
to line 424, FIGS. 10 and 11. The differentiator circuits 411, 357
and 477 are eliminated as previously mentioned. Then either the
lines 408 or 410 are connected. Subsequently, when the DON'T WALK
Interrupt Command line is activated, this line voltage is coupled
separately through diodes from line 424 to the reset terminals of
Bistables 418, 420 and 422. In the reset state, these Bistables
respectively release relays 426, 428, and 430 and apply AC power
from line 284 through the respective relay contacts to all DON'T
WALK lamp indicators. This circumstance maintains throughout the
subsequent Amber lamp command. The WALK lamp indicators for a given
street are illuminated when the associated R lamp indicators for
both directions of the street are activated.
The Emergency Control Commands constitute a unique feature of the
interface circuitry under discussion. The essential elements of
this part of the circuitry are shown in FIG. 12. The purpose of
emergency commands is to facilitate emergency vehicle flow through
intersections. The procedure to be described would be particularly
useful for emergency vehicle travel on through-streets in congested
areas. The scheme permits interruption of the usual traffic signal
cycle at any intersection under remote control, and imposes
emergency vehicle controls. For instance, if an emergency vehicle
is proceeding along Street No. 1 through an intersection, the
Street No. 1 Green Lights may be placed in the state of Rapid
Flashing Green, while the lights for intersecting streets No. 2 and
No. 3 may be placed in the state of Rapid Flashing Red.
Alternatively, an emergency vehicle may be proceeding along Street
No. 2 or No. 3. In either of these cases, Rapid Flashing Green
could be imposed on the street containing the emergency vehicle,
and Rapid Flashing Red could be imposed on intersecting
streets.
Other emergency vehicle procedures could be utilized. For instance,
all traffic lights at an intersection might be placed in the state
of Rapid Flashing Red. However, such a procedure usually will not
result in rapid clearance of the intersection.
It is possible to permit an emergency vehicle interrupt command at
any time during any part of the traffic signal cycle. However, the
simplest procedure would permit an emergency command only during
the Green or Amber time interval for one of the streets at an
intersection. Therefore, if a Left Turn Green Command existed at
the time desired for an emergency vehicle interrupt, the actual
Emergency Command can be delayed or not transmitted from the
Central Facility 10 until a subsequent Green Command has been
issued. This procedure permits the use of simple circuitry for the
Emergency Commands. In any case, the maximum delay which would be
experienced at any intersection would amount to only a few seconds.
The issuance of an Emergency Command during a Green or Amber time
can be controlled easily by the software package of the Central
Facility computer equipment.
With reference to FIG. 12, assume that an emergency command is to
be issued for one of the Streets, No. 1, No. 2 or No. 3. Detection
and processing of the particular Emergency Command in Logic 264 of
FIG. 8 will apply a positive voltage to one of the Emergency Lines
No. 1, or No. 2, or No. 3, in FIG. 12. This voltage is
differentiated and a positive pulse is coupled from whichever
Emergency line is activated to all Amber input lines No. 1, No. 2
and No. 3 via line 283. From previous discussions it is noted that
whenever a particular Green Command is active, the associated Amber
Line AND Gate for that street is also enabled. Therefore, when any
one Emergency Line is activated, the coupled positive voltage pulse
to all Amber lines will, of necessity, activate one and only one of
the Amber lamp circuits. The particular Amber lamp circuit which is
activated will be that one which corresponds to the same street
with the active Green Command.
Assume No. 1 Emergency Command is issued in FIG. 12, when the No. 2
Green Command is active. Coupling of the positive voltage pulse
from No. 1 Emergency line via line 283 to the respective Amber
lines No. 1, No. 2 and No. 3 will activate the No. 2 Amber lamp
circuit. As described previously, the usual circuit functions will
occur.
All Emergency lines are also coupled through diodes to line 447,
which is coupled to Delay Monostable 444. This monostable may be
arranged to output a pulse which is delayed by several seconds, say
4 seconds, which represents the time for the Amber light interval.
The delay pulse output from Delay Monostable 444 sets Bistable 442.
In a set state, Bistable 442 activates a Relay 446. In addition,
the output of Delay Monostable 444 is coupled via line 351 to the
set terminal of No. 1 Amber Bistable 360 and to the reset terminals
of No. 2 Amber Bistable 402 and No. 3 Amber Bistable 478.
Therefore, when the No. 1 Emergency line is activated, as mentioned
above, the No. 2 Amber lamp circuit will be activated for 4
seconds, at which time the No. 2 Amber Bistable 402 will be reset.
In a reset state, Bistable output causes deactivation of the No. 2
Amber lamps. When Relay 446 is activated, AC power on line 282 is
transferred by means of contacts 330 of Relay 446 to a Rapid
Flasher 456. The Rapid Flasher output is coupled back to line 332
and supplies rapid bursts of AC power to line 332. In addition, a
second output from Bistable 442 is used to enable AND Gates 448,
450 and 452. In the present instance, No. 1 Emergency line is
activated and this voltage is coupled through AND Gate 448 to the
set terminal of the No. 1 Green Command Bistable. Therefore, the
No. 1 Green Command function is executed, with the exception that
all lamp circuit power is now in the rapid flashing mode. Thus, for
the No. 1 Emergency Command, a pair of G lamp indicators 458 and
460 for Street No. 1 and R lamp indicators 374, 372 and 390, 392
for Streets No. 2 and No. 3 will continually flash on and off. If
No. 2 Emergency Command had been issued, G lamp indicators 384 and
394 for Street No. 2 and R lamp indicators 338, 340 and 390, 392
for Streets No. 1 and No. 3 would continually flash on and off. The
No. 3 Emergency Command causes a corresponding rapid flashing for a
pair of G lamp indicators 462 and 464 for Street No. 3, and for R
lamp indicators 338, 340 and 374, 372 for Streets No. 1 and No.
2.
In the event that DON'T WALK signals are utilized, the input line
to Delay Monostable 444 may be coupled through a diode to the DON'T
WALK Interrupt line, as shown in FIG. 12.
Differentiator 441 is coupled to line 447 so that, when an
Emergency Command is terminated, a negative pulse is output from
Differentiator 441 to Flip-Flop 455. This Flip-Flop 455 may be
adjusted to immediately output a positive pulse of, say, four
seconds duration. This output pulse is coupled to all input Amber
lines via line 283. Therefore, the appropriate Amber lamp circuit
will be activated for a 4 second period. In the present instance,
after termination of the No. 1 Emergency Command, the No. 1 Amber
circuit will be activated for 4 seconds. Subsequently, commands to
No. 2 or No. 3 streets are possible.
If a communication link failure were to occur while in the Remote
Control Mode, any possible command might be currently active.
Therefore, it is necessary to progress in a safe manner from the
interruption of the Remote Control Mode back to the Local Control
Mode. This can be accomplished by the resultant output pulse on
line 283 from diode 285, FIG. 9. If failure occurs during a No. 2
or No. 3 street Green or Left Turn Command, the associated Amber
line AND Gate will be enabled. Therefore, the positive voltage
output from diode 285 via line 283 to these Amber lines will
activate the appropriate Amber circuit. Four seconds later, Delay
Monostable 278, FIG. 9, will reset Bistable 276, and the Local
Control Mode will be re-established. The same sequence will also
occur for No. 1 street. If the failure occurs during the No. 1 Left
Turn Command, when this command is removed due to the failure, the
inverter 415, FIG. 10, will couple a pulse to the Green Command
Bistable. When the G lamp indicators, 458 and 460 are illuminated,
the No. 1 Amber line AND Gate will be enabled. Then circuit
response is as described above for streets No. 2 and No. 3.
It should be evident that the interface equipment discussed above
can be altered in a number of ways to facilitate applications of
other desired functions. For example, some municipalities prefer to
maintain a Green Signal illumination when the Amber signal for the
same street is illuminated. This function can be attained by
removal of the differentiator circuits 411, 357, and 477, and
connecting the dashed lines 408, as previously discussed. In
another circumstance, some municipalities may not desire to
interrupt the Local Control Mode during an Amber illumination
period. Corresponding circuit changes can be made to accommodate
these different functions.
It should be evident, also, that considerable circuit
simplification is possible when the required number of functions
are reduced. An example is shown in FIG. 13 for a very simple
two-street intersection. It is noted that remote control of this
circuit can be maintained by the use of two binary bits. Thus, the
first binary bit can be utilized to designate the control mode,
either Remote or Local Control. A second binary bit could be
utilized to control No. 1 Street Green, for instance, by means of a
zero bit value of the second binary bit in the command signal. A
one value of this binary bit would then control No. 2 Street Green.
Further, it is noted that the respective Amber light illuminations
occur automatically when the Green Command is changed in the
circuitry of FIG. 13. Finally, it is noted that elimination of all
input Amber Commands could be realized for circuitry such as is
shown in the previous FIG. 10. Appropriate usage of delay
monostable circuits could be accomplished such that fixed Amber
signal times would occur for the appropriate streets. An example of
this usage of delay monostable circuits is indicated in the
following circuit description for FIG. 13.
If the simple traffic functions depicted in FIG. 13 were the only
requirements for all Remote Transceivers 26 attached to a single
communication line, a total of 240 separate remote units or
terminals could be serviced on the communication line. This total
number of units includes the assumption of a 1,200 Hz bit rate and
an assumed maximum one-way transmission delay of 2.5 milliseconds
to reach remote unit. As mentioned previously, this total number
can be increased by increasing the bit rate or by more careful
compensation for possible transmission delay time.
Since only two command bits are assumed for the remote control of
lamp circuits in FIG. 13, the Logic circuitry 501 will be simpler
than that depicted previously in FIG. 9 for Logic 262.
Specifically, all items in FIG. 9 would be eliminated except AND
Gate 266, Bistable 276, Relay 368, and Diode 279. These remaining
items could suffice as Logic 501 circuitry.
In operation of the circuitry shown in FIG. 13, it has been assumed
that the Remote Control interrupt has occurred when the No. 2
Street Amber lights are illuminated. Therefore, a pair of R lamp
indicators 482 and 484 for No. 1 Street are also illuminated by
means of AC power from a line 284 through the contact of a Relay
488. The initial command would be No. 1 Green Command. For
instance, when a positive voltage is applied to the No. 1 Green
line, this voltage may be coupled to a Bistable 490 and to a Delay
Monostable 492. Normally, this voltage would reset Bistable 490,
whose output would release a Relay 494, and the No. 2 Amber lights
would be illuminated. In the present instance, No. 2 Amber lights
are already illuminated. When the positive voltage is applied to
Delay Monostable 492, this circuit generates a delays output pulse,
the delay being adjusted to whatever time interval is desired for
the No. 2 Amber light illuminations. The delayed output from Delay
Monstable 492 is coupled to and sets Bistable 490. In the set
state, Bistable 490 activates Relay 494, and AC power from line 284
is removed from the No. 2 Amber lights. Delay Monostable 492 also
is coupled to a Flip-Flop 496, whose output enables an AND Gate
498. Therefore, the No. 1 Green line voltage is coupled to and sets
a Bistable 500. Initially, Bistable 500 is in the reset state. When
in the set state, Bistable 500 activates a Relay 502, Relay 488,
and a Relay 504. For Relay 502, AC power is applied to a pair of G
lamp indicators 506, 508 for Street No. 1. For Relay 488, AC power
from line 284 is removed from the R lamp indicators 482, 484 for
Street No. 1. For Relay 504, AC power is applied to a pair of R
lamp indicators 510 and 512 for Street No. 2. This condition
maintains until the No. 1 Green Command is terminated and the No. 2
Green Command is initiated.
When the No. 2 Green line is energized, a positive voltage is
coupled to a Bistable 514 and to a Delay Monostable 516. This
voltage sets Bistable 514. In the set state, Bistable 514 activates
a Relay 518 and AC power is applied to the No. 1 Amber lights. The
voltage input to Delay Monostable 516 initiates a delayed output
pulse, the delay being adjusted to that desired for the No. 1 Amber
light illumination interval. The output of Delay Monostable 516 is
coupled to Bistables 514 and 500 and to a Flip-Flop 520. The output
of Delay Monostable 516 resets Bistables 514 and 500, releasing
Relays 502, 488, 518 and 504. Therefore, AC power is removed from
the G lamp indicators 506, 508 for Street No. 1. Also, AC power is
coupled from line 284 to the R lamp indicators 482, 484 for Street
No. 1. In addition, AC power is removed from the Amber lights of
Street No. 1 and from the R lamp indicators 510, 512 for Street No.
2. Delay Monostable 516 also activates Flip-Flop 520, whose output
enables an AND Gate 522. Therefore, the positive voltage on No. 2
Green line is coupled to and sets a Bistable 524. In the set state,
Bistable 524 activates a Relay 526 and AC power is applied to a
pair of G lamp indicators 528 and 530 for Street No. 2.
Through the use of Delay Monostables, as discussed in relation to
FIG. 13, it is possible to eliminate the need for Amber lamp
commands and DON'T WALK Interrupt commands. In addition, it is
possible to permit locally actuated devices, such as Left Turn
Vehicle Lane Detectors, to operate in parallel with a Remote
Control Mode. In such a situation, the remote commands for Left
Turns would not be necessary. The previously described circuits
could be utilized with appropriate modifications. For instance, a
local vehicle actuated Left Turn Command could preempt the
associated Remote Control Green Command when this command was
received at the remote unit. When vehicle actuation ceased or after
a predetermined maximum length of time for the Left Turn, the
Remote Control Green Command could be actuated.
Finally, it is noted that a given Green Command can be executed,
delayed, or changed in time increments which are less than one
communication cycle time. This function can be readily accomplished
by utilizing more than one Green Command per street. For instance,
three Green Commands for No. 1 street might be used as G1, G2 and
G3. Each of these separate green Commands would be represented by a
discrete command bit pattern. Therefore, each of these separate
Green Commands would be output from Logic circuitry 264, for
instance, on three separate lines. For one of the three lines, a
delay of 0.6 seconds could be inserted, and for a second line a
delay of 1.3 seconds could be inserted. Therefore, Green Commands
could be initiated in increments of approximately 0.7 seconds,
instead of the usual 2 second increments for a 2 second
communication cycle time.
VI. DESCRIPTION OF PREFERRED INTERFACE EQUIPMENT FOR RESPONSE
DATA FOR THE COMMUNICATION LINK SYSTEM
An illustrative example of interface circuitry which can be
utilized for coupling response signals from the traffic lamp
indicators at a given intersection to the associated remote unit is
shown in FIG. 14. Inputs to the circuit are labeled 288 through
328. These may be obtained, for instance, as input voltage as shown
in FIG. 10. The 288 through 324 inputs are connected to the
different traffic lamp circuits, such that when AC power is applied
to a particular lamp circuit, AC voltage is also coupled to the
correspondingly numbered R input. The 326 input occurs from line
282, shown in FIGS. 9 and 10, and is representative of the Remote
Control Mode. The 328 input occurs on closure of Emergency Relay
426 and is representative of the Flashing Mode for lamp indicators
under Emergency Vehicle Control.
In FIG. 14, each of the inputs 288 through 324 may be coupled
separately to two individual channels. One channel is input to a
first Logic Network 532, and the second channel is input to a
second Logic Network 534. When any particular command has been
correctly executed, there will exist a discrete set of traffic lamp
lamp indicators which are not active and a second discrete set of
traffic lamp indicators which are active. For any given command,
the particular traffic lamp indicators belonging to each set is
known. Thus, for Logic 532, a particular group of R inputs may be
coupled together through OR gates to comprise the No. 1 line output
from Logic 532. This group of R inputs comprises a representation
of those lamp indicator circuits which should not be activated when
some specific command has been correctly executed. For instance,
line No. 1 output from Logic 532 could correspond to the No. 1
Green Command. Thus, the 390 through 294, 298 through 302, 308
through 316 and 322 through 324 inputs will be logically OR'd to
line No. 1 output from Logic 532. Correspondingly, for this same
command, the 288, 296, 304, 306, 318 and 320 inputs will be
logically AND'd in Logic 534 to comprise line No. 1 output from
Logic 534.
In a similar manner, the appropriate R inputs for other commands
can be logically OR'd for No. 2 through No. 10 output lines from
Logic 532, and other appropriate R inputs for the same
corresponding commands can be logically AND'd for No. 2 through No.
10 output lines from Logic 534. For instance, line No. 2 can
correspond to No. 2 Left Turn Green Command, line No. 3 to No. 1
Left Turn Green Command, line No. 4 to No. 3 Left Turn Green
Command, Line No. 5 to No. 1 Amber Command, line No. 6 to No. 2
Green Command, line No. 7 to No. 3 Green Command, line No. 8 to
DON'T WALK Interrupt Command, line No. 9 to No. 2 Amber Command,
and line No. 10 to No. 3 Amber Command. Therefore, when any of
these commands has been executed correctly, the correspondingly
numbered output line from Logic 532 circuitry will not be energized
and the correspondingly numbered output line from Logic 534
circuitry will be energized. The remaining three lines No. 11, No.
12 and No. 13, correspond, respectively, to No. 3 Emergency, No. 2
Emergency and No. 1 Emergency Commands.
The output lines from Logic 532 and Logic 534 may be coupled
separately to a third Logic Network 536. For instance, Logic 536
may be arranged as depicted in FIG. 14. Each input line from Logic
534 can be logically OR'd in an OR Gate 538, within Logic 536. For
any command which has been correctly executed, one and only one of
the input lines from Logic 534 will be energized. This voltage will
be coupled through OR Gate 538 to a Bistable 540. With voltage
input to Bistable 540, an enabling gate is coupled to an AND Gate
542 from the output of Bistable 540. In addition, each numbered
input line from Logic 534 can be coupled to and utilized to enable
a correspondingly numbered AND Gate, within Logic 536. The
correspondingly numbered input lines from Logic 532 can be coupled
to each of the same numbered AND Gates, within Logic 536. An
example of this coupling within Logic 536 is shown in FIG. 14 for
an AND Gate 544 and the number 5 input lines. The outputs of all
AND Gates within Logic 536 can be logically OR'd in an OR Gate 546.
For any command which has been correctly executed, one and only one
of the AND Gates within Logic 536 will be enabled. The particular
AND Gate which is enabled will correspond to the particular
executed command. Also the correspondingly numbered line output
from Logic 532 which is coupled to this enabled AND Gate will not
be energized. Therefore, there will be no input to OR gate 546
within Logic 536, and consequently, no output from OR Gate 546 to
Bistable 548. A Bistable 548 may be arranged so that an output gate
is coupled to AND Gate 542 when no input voltage is supplied to
Bistable 548. Since AND Gate 542 is enabled by Bistable 540, the
gate voltage from Bistable 548 is coupled through AND Gate 542 to a
group of bit AND Gates 550 through 556. These bit gates permit data
bits to be coupled to the Response AND Gates in the Remote
Transceiver, FIG. 7.
If any command has been executed incorrectly, or if a circuit
malfunction has occurred, one of two circumstances will exist for
the output lines from Logic 534. The first circumstance will occur
when more than one output line from Logic 534 is energized. The
second circumstance will occur when none of the output lines from
Logic 534 is energized. For the latter case, there will be no input
to or output from OR Gate 538 within the Logic 536. Consequently,
Bistable 540 will not be activated, AND Gate 542 will not be
enabled, and the bit AND gates 550 through 556 will not be enabled.
Therefore, no discrete command bit data can be transmitted back to
the Central Facility 10. If more than one output line from Logic
534 is energized, at least two AND Gates within Logic 536 circuitry
will be enabled. Since at least one of the enabled AND Gates is
incorrect, it is most probable that the line output from Logic 532
which is coupled to this incorrectly enabled AND Gate will be
energized. This is because is is almost impossible for all of the R
inputs to this line to be inactive. In such a circumstance, OR Gate
546 within Logic 536 will pass the energized line voltage to
Bistable 548. With an input voltage, Bistable 548 will not output a
voltage gate. Therefore, there will not be a voltage gate output
from AND Gate 542, in spite of the fact that AND Gate 542 may be
enabled from the output of Bistable 540. Consequently, the bit AND
Gates 550 through 556 will be disabled, and no discrete command bit
data can be transmitted back to the Central Facility 10.
The output lines from Logic 534 are also coupled appropriately to
the four bit lines. Therefore, when any command has been executed
correctly, the correspondingly numbered output line from Logic 534
will be energized. This voltage will be coupled to the correct bit
lines by means of indicated diodes. The bit line voltages are
coupled through the enabled bit AND Gates 550 through 556 to the
attached Remote Transceiver 26.
The Remote Control mode is evidenced by an energized 326 R input
voltage. This voltage may be coupled directly to the appropriate
Response AND Gate in the attached Remote Transceiver 26.
The Flashing Mode for Emergency Vehicle Control signals is
evidenced by an energized 328 R input voltage. This voltage may be
utilized to enable a group of AND Gates 558, 560 and 562. The
corresponding Emergency Command, when executed correctly, will
energize one of the output lines No. 11, No. 12, or No. 13 from
Logic 534. These Emergency Command lines also are appropriately
coupled through one of the enabled AND Gates, 558, 560 or 562 to
the appropriate bit lines.
It is noted that the disclosed Communication Link System can also
be utilized to detect and transmit information relative to a burned
out traffic lamp indicator. If a 1/2 ohm (or less) dropping
resistor were inserted in each lamp indicator circuit, the voltage
drop across this resistor could be detected when the lamp circuit
is active. When a lamp indicator is burned out, the voltage drop
will decrease on a line which accommodates several lamp indicators
in parallel, or the voltage drop would be eliminated if only one
lamp indicator were attached to the line. The decrease or
elimination of a voltage drop, when it occurs, can be coupled to
appropriate logic circuitry, and transmitted back to the Central
Facility 10. For a large metropolitan area with many remotely
controlled traffic lights, this feature will reduce maintenance
crew expense by a significant amount.
An example burn-out detection circuit is shown in FIG. 15. The AC
voltages present at each terminal of the dropping resistor 580 are
voltage-divided and half-wave rectified by a pair of diodes 564 and
566. The 564 diode rectified output voltage may be filtered by a
Capacitor 568, and furnishes collector voltage to a pair of
Transistors 570 and 572. The 566 diode rectified output voltage
furnishes base voltage to Transistor 570. When AC voltage is
applied to the lamp circuit, the collector of Transistor 572 will
be established at some relatively stable value of voltage at an
output 574, dependent on the transistor characteristics and the
associated resistor values. The voltage value at output 574 is
adjusted such that a Zener diode 576 will not conduct. That is, the
voltage level at output 574 is too small to cause conduction in
Zener diode 576. However, when a lamp indicator burn-out occurs,
the rectified voltage increase at diode 566 raises the base voltage
of Transistor 570. This action decreases the collector voltage of
Transistor 570, which is directly coupled to the base Transistor
572. Therefore, the collector of Transistor 572 rises to some
higher value, sufficient to cause conduction of Zener diode 576.
When the Zener diode conducts, a voltage is produced at an output
578. It is noted that when the lamp indicator circuit is removed
from input AC power, the collector voltages of Transistors 570 and
572 are also removed. Therefore, no voltage is produced at output
578. This feature is useful since a voltage output at 578 only
occurs when the voltage drop across a dropping resistor 580 is less
than a predetermined value. Therefore, the 578 outputs for all lamp
indicator circuits at a given intersection can be logically OR'd in
an OR gate 582. If any one lamp circuit contains a burned-out lamp,
there will be a resultant voltage output from the OR gate 582.
The output of OR Gate 582 can be coupled to a Monostable 584. When
the output of OR Gate 582 is zero, the output of Monostable 584 may
be adjusted to disable and AND Gate 586. When the OR Gate 582
produces an output voltage, the output of Monostable 584 may be
adjusted to enable AND Gate 586. The input to AND Gate 586 can be
attached to the No. 1 line output from Logic 534 of FIG. 14. This
line is energized only when the No. 1 Green Command has been
executed correctly. Therefore, when the output of OR Gate 582 is
zero, representing no burn-out for any lamp indicator, AND Gate 586
will be disabled, and there will be no output.
When the OR Gate 582 outputs a voltage, representing at least one
burned-out lamp indicator, AND Gate 586 will be enabled.
Subsequently, each time the No. 1 Green Command is executed, the
voltage on line No. 1 from Logic 534 will be coupled through AND
Gate 586. AND Gate 586 is coupled to the No. 5 bit line. Therefore,
the No. 1 Green Command will appear as the four-bit command signal
of 1001. When the Remote Control Mode bit is added, the 5-bit No. 1
Green Command would appear as 11001. When this response signal is
transmitted via the remote unit to the Central Facility 10,
detection of the response bits 11001 may be accessed as a No. 1
Green Command response plus the additional information, contained
in the last binary bit value of one, that there exists a burned-out
traffic lamp indicator at the remote unit location which produced
the information. Finally, it is noted in FIG. 15, that the 574
outputs from the various lamp circuits may be utilized as the R
input signals 288 through 324 in FIG. 14, without the need for
additional circuitry to supply these input signals.
VII. DESCRIPTION OF PREFERRED CIRCUITRY FOR SIGNAL
RESPONSES OTHER THAN TRAFFIC LAMP INDICATOR CIRCUITS
FOR THE COMMUNICATION LINK SYSTEM
It has been mentioned previously that Remote Transceivers 26 may be
utilized with vehicle detection devices. Also, if an auxiliary
receiver circuit is added to a remote unit, a means exists for
processing information relative to the presence of emergency
vehicles or other vehicles which may be under control of the
various service departments of a municipality.
On-the-street vehicle detection devices are currently utilized in a
number of different ways. In general, these functions may remain
unaltered under the Remote Control Mode for the Traffic and
Transportation Communication Link System. The application of the
Communication Link System, however, provides a unique means for
transmission of all vehicle detection data to the Central Facility
10, if such data are desired at the Central Facility. A vehicle
detection device which detects vehicle presence only would require
only one binary bit output to convey this information. Thus,
vehicle presence could be indicated by a one value of the binary
bit and vehicle absence would be indicated by a zero value of the
binary bit. A vehicle detection device which is used to count
vehicles or to determine vehicle movement or speed, in general,
will require the use of two binary bits, if these data are to be
transmitted to the Central Facility. For instance, for moving
vehicles between 10 mph and 70 mph, a single vehicle counter for
one traffic lane would be required to count at a rate no faster
than one vehicle per second. Usually, this count rate would be from
1.5 to 2 seconds per vehicle. Therefore, for a communication cycle
time length of about 2 seconds, a maximum count rate of two
vehicles per communication cycle time would be experienced. Thus,
two binary bits can be utilized to convey this information.
Furthermore, at a simple two-street intersection with control
functions as depicted in FIG. 13, the two vehicle detection bits
from a nearby vehicle detection device could be processed in the
remote unit, together with the response command data signals, which
correspond to the traffic lamp indicators. This would be possible,
also, for intersections which require three bits of response
command data, since each remote unit is permitted a response time
interval equivalent to a 5-bit response signal.
Other installations may require inputs from several vehicle
detection devices which may be located nearby to a given remote
unit. In such cases, the response time interval for a given remote
unit may be increased from one interval to two, three, or more
response time intervals. For instance, let it be assumed that three
response time intervals were allotted to a given remote unit, for
an intersection which required 3-bit commands. A 3-bit command
could permit four remotely controlled traffic functions at the
intersection. In such a circumstance, the use of three response
time intervals for the attached remote unit would permit data from
six vehicle detection devices to be processed, together with the
response command data for the given intersection. It is noted,
however, that an increase of the response time interval for any
given remote unit will decrease the total time available for
responses from other remote units attached to the same
communication line. Therefore, the total number of possible remote
units on the communication line would be reduced. For the circuitry
discussed in relation to FIG. 10, there is ample communication
cycle time available for command and response of at least 150
separate remote units attached to the same communication line.
Therefore, if two response time intervals were allotted to one of
these remote units, the total number of possible remote units would
be reduced from 150 to 149, for the communication line.
It is noted that any vehicle detection device or a group of vehicle
detection devices may be utilized together with their own dedicated
Remote Transceiver 26. The data output from each vehicle detection
device may be processed, for instance, to the form of binary data
bits and input to the response circuits in the receiver section of
the attached Remote Transceiver 26. A preferred embodiment of such
circuitry is shown in FIG. 16. It has been assumed that two
response time intervals have been allotted to the attached Remote
Transceiver 26. For this case, six Vehicle Detection Devices or
Vehicle Detectors 30 may utilize the same remote unit. Thus, six
inputs 588 and 598 are shown in FIG. 16. Each input is assumed to
result from an attached Vehicle Detection Device 30 which is
counting vehicles. If Two Counters are utilized, as illustrated at
600 to 610, when 1 count is received, the corresponding 1 count
line to one of the attached Monostables 612 to 632 would be
energized. For instance, if 1 count were received for the No. 1
Vehicle Detection Device over line 588, Monostable 612 would be
activated. The output of Mono stable 612 can be coupled to a
Response AND Gate 254 in the response circuitry of the receiver
section, FIG. 7, of the attached Remote Transceiver. When Response
AND Gate 254 is enabled at the appropriate response time, the
binary bit value of one would be inserted into the OR Gate 256,
FIG. 7. Subsequently, when a second count is received from the No.
1 vehicle detection device on the 588 count line FIG. 16,
Monostable 614 would be energized and a binary bit value of one
would be coupled to Response AND gate 252.
When Response AND Gates 252 and 254 are enabled in a serial manner
in the receiver section at the appropriate response time, the
binary bit values input to OR Gate 256 could comprise any one of
the following sets of values. First, both bit values could be zero,
indicating no vehicle counts. Second, the first bit value could be
zero and the second bit value could be one, indicating one vehicle
count. Third, the first bit value could be one and the second bit
value could be zero, indicating two vehicle counts. If the
Two-Counter were replaced with a Three-Counter, a fourth
circumstance could be accommodated, if desired. Thus, an additional
Monostable could be added, such that its output enabled,
simultaneously, both Response AND Gates 252 and 254. Therefore, the
binary bit values of one and one could indicate three vehicle
counts. Similar results would occur from the remaining inputs 590
through 598 in FIG. 16.
The Two-counters 600 through 610 may reset once each communication
cycle time by the same pulse utilized to reset the Response Counter
250 circuit of FIG. 7. In the present circumstance, where two
response interval times are allotted to a given remote unit, the
Response Counter 250 in FIG. 7 would still be reset on the n + 2
count. However, the value of n would be 12 in the present
circumstance. Therefore, the total discrete response time interval
for the attached remote unit would be equivalent to 13 bit times.
This results because the assumed one-way transmission delay of 2.5
milliseconds would not be necessary between the two sequential time
response intervals. This is because the response bits contained in
both time response intervals are all transmitted from the same
remote unit. Thus, the additional 2.5 milliseconds of time, which
is available, can be utilized to process data from the sixth
additional vehicle detection device. Actually, in the present
circumstance, only 12 of the available 13 bit times are utilized to
transmit the 12 bits from the six vehicle detection devices.
Finally, the presence of any suitably equipped vehicle may be
detected at any given intersection. For instance, if an emergency
vehicle is equipped with a transmitter and if a suitable receiver
is attached to a given remote unit, the presence of this vehicle in
the vicinity of the remove unit may be detected. This information
may then be transmitted to the Central Facility 10. For instance,
let it be assumed that a low power transmitter is attached to a
vehicle, such that a transmission range of 250 to 350 feet is
available. Further let it be assumed that a suitable receiver is
attached to a Remote Transceiver 26, located at a given
intersection. The vehicle may be assigned a number from 1 to 31.
These numbers respresent the different possible combinations of a
5-bit response signal, neglecting the response signal of 00000.
Whenever, this vehicle is within, say, 250 feet of the given
intersection, the receiver detects the particular transmitted
signal from the vehicle. The output of the receiver can be
processed, such that unique data bits, representative of this
particular vehicle, may be input to the response circuitry of the
receiver section of a Remote Transceiver 26. These data may then be
transmitted back to the Central Facility 10 during the appropriate
response time interval assigned to the remote unit. In larger
metropolitan areas, there would exist, in general, a need for
representation of a larger number of vehicles than the 31 possible
with a 5-bit response signal. If two response time intervals were
allotted to the remote unit, a total of 1,024 separate vehicles
could be detected.
In some instances, it might be desirable to maintain surveillance
of several emergency vehicles in the vicinity of an intersection,
for instance, in the case of a major accident. In such a
circumstance, transponder equipment and/or separate frequencies
might be utilized for the emergency vehicles. In any case, the data
received from each emergency vehicle may be stored and processed in
a serial manner, once each communication cycle. For instance, if
the communication cycle were two seconds, data corresponding to
each emergency vehicle present might be transmitted serially, one
vehicle per communication cycle. For 10 vehicles present, 10
communication cycles would be required for transmittal of the
separate data relating to the presence of each emergency vehicle.
The total time required in this instance would be approximately 20
seconds.
* * * * *