Marshall A Martin

US Patent:

46807179, Jul 14, 1987

Filed:

Sep 17, 1984

Appl. No.:

6/651480

Inventors:

Marshall H. Martin - Northridge CA

Assignee:

Indicator Controls Corporation - Gardena CA

International Classification:

G08G 107
G08G 101

US Classification:

364436

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.