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Consider the traffic light to view the traffic lights. The normal sequences for traffic lights are light green in one direction for a long time, usually 10 or more seconds. Followed by a brief yellow light, typically 4 seconds. This follows a similar pattern of light in the opposite direction. It is clear that the light green or yellow in one direction implies a red light in the opposite direction. Pedestrian buttons are provided so that when pedestrians are present across the walk light can be switched on and a length of green light increases.

Traffic Light Project

The first step in the development of controller is to define the inputs and outputs of the system, as shown in See Inputs and Outputs for Traffic Light Controller. Before we describe the system variables. They differ in how the system moves from one state to another. Please note that some of this information can define the state (not only states). Inputs are used to define transitions. Outputs can be used to define the system state.

Step First :This Exemple diagram of I/O with show process of light

Inputs and Outputs for Traffic Light Controller

State diagrams above were used to define the system, you can use the state table, as shown in the system of state See table at the traffic lights. Here the light sequences are listed in order. Each state is given the name of ease of interpretation, but the corresponding model output is also given. The system state is defined as the bit pattern of lights 6. Note that there are only 4 models, but 6 binary bits can comprise up to 64 years.

Step second : Define System state in process

System State Table for traffic lights

Transitions can be added to the table to clarify the status of activity, as shown in Table V. transition state. Here the transition from Green E / W Yellow E / W is S1. This means that walking through the button must be pushed to the end of the green. This is not normal, normally the lights would use the delay. The transition from yellow or green N / S delay is caused by 4 seconds (this is normal.) The next step is abnormal, requiring them to walk through the button pressed until the end of the Green N / S State. Last state has a delay of 4 seconds before returning to the first state in the table. In this state table the sequence is always the same, but times have changed to green.

Step Third : Define and Show State transistion trigger and add them to state table

State Table with Transitions

State diagram for the system is given in See Traffic Light State Diagram. This scheme is equivalent to the state table in Table View with state transitions, but may be useful for visual inspection.

Step Four : Create and Draw state transition diagram

Traffic Light PLC ladder

So,We can write ladder diagram in PLC software thus as picture below.

Step Five: Write PLC Ladder State Diagram

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