18-12-2010, 04:46 PM
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Traffic signal controller
Abstract :Traffic signal controller is playing more and more important roles in modern management and controls of urban traffic to reduce the accident and traffic jam in road. They assign the right of way to road users by the use of lights in standard colors (Red - Amber - Green), using a universal color code (and a precise sequence, for those who are color blind). They are used at busy intersections to more evenly apportion delay to the various users. The most common traffic lights consist of a set of three lights: red, yellow (officially amber), and green. When illuminated, the red light indicates for vehicles facing the light to stop; the amber indicates caution, either because lights are about to turn green or because lights are about to turn red; and the green light to proceed, if it is safe to do so. The traffic light controller is a sequential machine to be analyzed and programmed through a multi step process. The device that involves a analysis of existing sequential machines in traffic lights controllers, timing and synchronization and introduction of operation and flashing light synthesis sequence. The methods that are used in this project are design the circuit, write a coding, simulation, synthesis and implement in hardware.
HDL LANGUAGE : VHDL
SIMULATION TOOL : Xilinx 9.1i
FPGA FAMILY : SPARTAN 3E
1.1 INTRODUCTION:
Traffic lights, also known as traffic signals, stop lights, stoplight, traffic lamps, stop-and-go lights, robots or semaphore, are signaling devices positioned at road intersections, pedestrian crossings, and other locations to control competing flows of traffic.
Traffic lights have been installed in most cities around the world to control the flow of traffic. They assign the right of way to road users by the use of lights in standard colors (Red - Amber - Green), using a universal color code (and a precise sequence, for those who are color blind). They are used at busy intersections to more evenly apportion delay to the various users.
The most common traffic lights consist of a set of three lights: red, yellow (officially amber), and green. When illuminated, the red light indicates for vehicles facing the light to stop; the amber indicates caution, either because lights are about to turn green or because lights are about to turn red; and the green light to proceed, if it is safe to do so.
There are many variations in the use and legislation of traffic lights, depending on the customs of a country and the special needs of a particular intersection. There may, for example, be special lights for pedestrians, bicycles, buses, trams, etc; light sequences may differ; and there may be special rules, or sets of lights, for traffic turning in a particular direction. Complex intersections may use any combination of these.
Traffic light technology is constantly evolving with the aims of improving reliability, visibility, and efficiency of traffic flow.
Colors:
The most common colors used in traffic lights are red, amber (yellow), and green. Red typically means stop or high level of danger; amber typically means caution; and green typically means proceed with care.
Usually, the red light contains some orange in its hue, and the green light contains some blue, to provide some support for people with red-green color blindness. Some traffic lights typically have a white reflective border which enables color blind users, during the hours of darkness, to distinguish the lights from other similarly-colored street or automobile lights, and to allow them to distinguish the lights by vertical position.
1.3 Control and coordination
The normal function of traffic lights requires sophisticated control and coordination to ensure that traffic moves as smoothly and safely as possible and that pedestrians are protected when they cross the roads.
2.1 IMPLEMENTATION:
The traffic light controller can be implemented by using the state machines in the four directions. The initial state can be considered as the ‘north’ in which the yellow lights and green lights of remaining directions are 0’s and red lights of remaining directions are 1’s (where ‘0’ indicates OFF and ‘1’ indicates ON states). When the time is less than 10 seconds to the initial point the yellow light of north direction is ON i.e. made high and the red and green lights are made OFF i.e. made low. After 10 seconds the yellow light is made low and the green light is made high. This goes until 39 seconds. Once the time reaches 40 seconds the red light is made high with remaining two to be low. The state is then initialized to ‘west’ and the timer is once again set to zero.
