PLC based 4 Way Traffic Light Control System

We most often come across four way traffic jam in our city. This PLC ladder logic gives the solution to control city traffic  using programmable logic control.

4 Way Traffic Light Control

Problem Solution

1. They are so many ways to write a program for traffic light control ex: sequencer output method but in this normal input, outputs and timers are used.
2. Timers are used to give time delay for output to turn on and off.
3. Reset using timer done bit at the end to run the program continuously.
4. Program done in AB RSLogix 500 Software.

List of Inputs and Outputs

S.no	Address	Name	Input/Output
1	I:0/0	Start	Input
2	I:0/1	Stop	Input
3	B3.0	Memory	Memory
4	O:0/0	East Green	Output
5	O:0/1	North Red	Output
6	O:0/2	West Red	Output
7	O:0/3	South Yellow	Output
8	O:0/4	East Yellow	Output
9	O:0/5	North Yellow	Output
10	O:0/6	North Green	Output
11	O:0/7	East Red	Output
12	O:0/8	West Yellow	Output
13	O:0/9	West Green	Output
14	O:0/10	South Yellow	Output
15	O:0/11	South Green	Output

Sequence of Operation

Below tabular column gives the Steps or sequence of outputs to turn ON the traffic system lamps (RED, GREEN, YELLOW)

PLC Ladder Logic

Logic Description

RUNG000

Latching rung to operate the system through Master Start and Stop PB.

RUNG001

Starting the timer to turn on output East Green ,North-South-West are in red. Parallel circuits are added to turn ON/OFF the output in up next sequence.

RUNG 0002

Turning on North Yellow and East Yellow. Parallel circuits are added to turn ON/OFF the output in up next sequence.

Rung 0003

Turn on East Red and North Green.

Rung 0004-0005-0006-0007

Same procedures followed to turn on further outputs.( Refer Above Tabular column for sequence of operation)

RUNG 0008

Timer (T4:7) done bit is used to restart the cycle from beginning

Program runs continuously until STOP PB is pressed

Time delay of 10s has given using timers.

Note: We can reduce the number of timers using comparator block

Conclusion:

The above explained 4 ways traffic light control using PLC is for example only. It may vary from real time. We can use this example program to understand the working of timers and Interlocking function in AB PLC.

Author : Hema Sundaresan

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