0 Preface
The emergence of traffic lights enables traffic to be effectively controlled, which has obvious effects on diverting traffic flow, improving road traffic capacity, and reducing traffic accidents. In order to realize the management of traffic roads, we strive to be advanced and scientific in traffic management. The control system of traffic light control is realized by programmable controller S7-200 PLC, and the software and hardware design method of the system. The experiment proves that the system is simple and economical, can effectively divert traffic and improve the traffic capacity of traffic intersections. The status quo of modern urban traffic control and management problems is analyzed. The working principle of traffic light control system is expounded in combination with the actual situation of traffic. A simple and practical PLC design scheme of urban traffic light control system is given. Programmable controllers are extremely important in industrial automation and are used in a wide range of industries.
With the development of technology, the functions of programmable controllers are increasingly perfect, coupled with miniaturization, low price and high reliability, and the role in modern industry is more prominent.
1. Design requirements for traffic light control system
1.1 Simulation control system combined with traffic lights at intersections
In the PLC traffic light simulation module, the main road has three control lights on each side of the east, west, north and south, respectively:
â—No traffic lights (red when lit)
â— Prepare to disable the traffic light (yellow when lit)
â— Passing light (green when lit)
In addition, there are two control lights on each side of the sidewalk, north and south, respectively:
â—No traffic lights (red when lit)
â— Passing light (green when lit)
Design a traffic light simulation control system in combination with the actual situation of traffic lights at intersections. When the traffic light system start switch is turned on:
(1) The north-south (column) and east-west (row) main roads are equipped with green light 20S, green light shining 3S, yellow light 2S and red light 25S.
When the red light of the north and south main roads is lit, the main trunk roads should light green light in turn, green light flashes, yellow light. Conversely, when the red light of the main trunk road lights up, the north and south main roads light green light in turn, green light flashes, yellow light.
(2) Both north-south and east-west sidewalks are set to pass green light and forbidden red light. The green light of the north and south sidewalks should be lit when the green light of the north and south main roads is lit. When the green light of the north and south main roads is shining and the yellow light is on, the north and south pedestrian green lights should also be correspondingly shining, and the other time is red. The green light of the east and west sidewalks lights up when the green light of the east and west main roads lights up. When the green light of the east and west main roads is shining and the yellow light is on, the green light of the east and west sidewalks should be correspondingly shiny. The other time is red light.
(3) In addition to the other two functions, use 10 pulse switches. This allows the blind to easily control traffic flow through intersections and manually. Eight of them are installed on both sides of the sidewalk. When the blind person walking in the east-west direction wants to cross the road, press the pulse switch to turn the green light on the sidewalk, and the red light from the north-south main road flashes, delaying the original control system by 10 seconds. The north-south direction pulse switch has the same function as the east-west direction. The other two pulse switches can control the traffic flow. When the east-west main road waits for a large amount of traffic, press the east-west control pulse switch to extend the green light-on time of the east-west main road by 15 seconds. The east-west sidewalk green light should also be extended, and the north-south direction pulse switch has the same function as the east-west direction.
1.2 Crossroads traffic light simulation control timing diagram
The details are shown in Figures 1 to 4.
2. Design of traffic light control system
2.1 Programmable controller selection
This traffic light is designed from Siemens programmable controllers. Product specifications: S7-200 series is a kind of programmable logic controller. This series of products can meet the needs of a wide range of automation control. With its compact design, good expandability, low price and powerful instructions, the S7-200 can meet the requirements of small-scale control. It is characterized by compact structure, convenient use and strong adaptability. The disadvantage is that the number of input and output ports is fixed, mainly using small PLC.
2.2 Programmable Controller I/O Address Assignment
The Siemens module is a CPU224 type with 10 input addresses and 14 output addresses, which can meet the design requirements of traffic light control systems. Determining the I/O address is the first problem to be solved in designing the entire PLC traffic light control system. It determines the design of the hardware part of the system and is also the premise of system software programming. According to the design requirements of the system, there are 6 input addresses I0.0~I0.5 and 7 output addresses Q0.0~Q0.6. The specific input and output address definitions are shown in Table 1.
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