Microprocessor controlled loop detector system

• US 4,680,717 A
• Filed: 09/17/1984
• Issued: 07/14/1987
• Est. Priority Date: 09/17/1984
• Status: Expired due to Fees

• Current Assignee: Display Technologies, Inc. (Rhode Island)
• Original Assignee: Indicator Controls Corporation
• Inventors: Martin, Marshall H.
• Primary Examiner(s): Lall, Parshotam S.
• Assistant Examiner(s): Black, Thomas G.
• Application Number:
  US06/651,480
• Time in Patent Office: 1,030 Days
• Field of Search: 364/436, 364/438, 331/65, 340/933, 340/939, 340/909, 340/910, 340/911, 340/941, 340/917
• US Class Current: 701/117
• CPC Class Codes: G08G 1/042 using inductive or magnetic detectors
• CPC Class Codes: G08G 1/07 Controlling traffic signals

Abstract

A microprocessor controlled loop detection system to be connected to a number of inductive loops which are buried in a road bed and which is used to detect the presence of motor vehicles above the loops to control the operation of traffic lights at an intersection. A common oscillator is connected to each loop on a time-shared basis under the control of a microprocessor, and the frequency of the oscillator in each instance is dependent upon whether or not there is a vehicle above the loop. The microprocessor provides a null time as the system is switched from one loop to another to prevent spurious responses in the system due to transient signals. The microprocessor acts to count the number of cycles of the output signal of the oscillator which occur during a predetermined time interval as each loop is connected to the oscillator by the microprocessor to determine the oscillator frequency for each loop and thereby detect the presence of a vehicle in the particular loop. A synchronizing circuit is provided connecting the oscillator to the microprocessor for controlling the start and finish of each such counting interval by the microprocessor.

Claims

1. A microprocessor controlled detection system connected to a plurality of inductive loops buried in a road bed and used to detect the presence of motor vehicles over the respective loops, said system comprising:

a common oscillator circuit for generating an output signal of a particular frequency which is subject to change when a motor vehicle passes over any one of the loops;

a switching circuit for connecting respective ones of the loops on a sequential and cyclic basis to the oscillator circuit;

a microprocessor controller connected to said switching circuit for supplying switching signals to said switching circuit to enable said switching circuit sequentially and cyclically to connect the loops to said oscillator circuit;

an input circuit connecting said microprocessor controller to enable said microprocessor controller to count the cycles of the output signal from said oscillator as said loops are sequentially and cyclically connected to said oscillator;

an output circuit connected to said microprocessor controller for providing a plurality of separate output call signals in response to cycles of said output signal counted by said controller to indicate when a change has occurred in the frequency of the output signal from said oscillator beyond a pre-selected threshold when corresponding ones of said loops are connected to said oscillator circuit;

means in said microprocessor controller for providing a null time between each connection of said loops to said oscillator circuit by said switching circuit;

circuit means included in said input circuit for synchronizing the oscillator with the microprocessor controller so that the count by the microprocessor controller will commence upon the occurrence of a particular transition of the oscillator output signal after the controller has been conditioned to make a count after a particular loop has been connected to the oscillator by said switching circuit; and

a plurality of manually-operated command switches connected to said microprocessor controller, in which the manually-operated command switches include a plurality of on-off switches for deactivating different channels of said system, and means in said microprocessor controller responsive to the settings of the on-off switches for causing said microprocessor controller to supply switching signals to said switching circuit corresponding to less than all of the channels and without any dead time for the de-activated channels.

2. The microprocessor controlled detection system defined in claim 1, in which the command switches also include pulse/presence switches for each of the loops, and means in said microprocessor controller responsive to the settings of said pulse/presence switches for establishing each of said loops in either a pulse or a presence mode.

3. A microprocessor controlled detection system connected to a plurality of inductive loops buried in a road bed and used to detect the presence of motor vehicles over the respective loops, said system comprising:

a common oscillator circuit for generating an output signal of a particular frequency which is subject to change when a motor vehicle passes over any one of the loops;

a switching circuit for connecting respective ones of the loops on a sequential and cyclic basis to the oscillator circuit;

a microprocessor controller connected to said switching circuit for supplying switching signals to said switching circuit to enable said switching circuit sequentially and cyclically to connect the loops to said oscillator circuit;

an input circuit connecting said microprocessor controller to enable said microprocessor controller to count the cycles of the output signal from said oscillator as said loops are sequentially and cyclically connected to said oscillator;

an output circuit connected to said microprocessor controller for providing a plurality of separate output call signals in response to cycles of said output signal counted by said controller to indicate when a change has occurred in the frequency of the output signal from said oscillator beyond a pre-selected threshold when corresponding ones of said loops are connected to said oscillator circuit;

means in said microprocessor controller for providing a null time between each connection of said loops to said oscillator circuit by said switching circuit;

circuit means included in said input circuit for synchronizing the oscillator with the microprocessor controller so that the count by the microprocessor controller will commence upon the occurrence of a particular transition of the oscillator output signal after the controller has been conditioned to make a count after a particular loop has been connected to the oscillator by said switching circuit; and

a plurality of manually-operated command switches connected to said microprocessor controller, in which the command switches include an extend/delay switch, and means in said microprocessor controller responsive to the setting of said extend/delay switch for establishing a corresponding one of the loops in either an extend or delay mode.