Traffic Light Control using PLC Ladder Logic Programming

Design ladder logic for 4 way-traffic light control system

The traffic light is one of the classic examples in PLC ladder logic.

We can take four directions (North, South, west, and east) with three output lamps (Green, Red, and Yellow).

You can build your own concept for making logic for this example.

Follow below tabular column – Logic for the four way traffic light

Design ladder logic for 4 way traffic light control system

List of Inputs and Outputs

Inputs and Outputs of 4 way Traffic Light Logic

Traffic Light Control using PLC

Design PLC Ladder Logic for 4 way Traffic Light Control System
Traffic Light Control System
Traffic light using PLC Programming
Traffic Light Control PLC Program

Logic Explanation

Network 1

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

Network 2

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

Network 3

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

Network 4

Turn on East Red and North Green.  

Network 5, 6, and 7

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

Network 8

Timer 7 (T7) done bit is used to restart the cycle from beginning

Program runs continuously until STOP PB is pressed

Time delay of 5s has given using timers which will make each cycle with 5s delay.

Author: Hema

Training Course: Siemens PLC Training

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  1. This illustration was very helpful. From it, I also learned that there is more than one way to obtain a desired result.
    Thank you so much

  2. I have a doubt in Network 2 and 8.
    After the Timer T7 in Network 8 runs for 5 seconds, won’t the N/C contact of T7 in Network 2 become open ? If it opens how will output coil Q0.0 and Q0.1 will get energized? Thus, how reset action will occur ?
    Kindly clarify my doubt.

  3. 1) I have doubt in n/w 2 Q0.1(North-red) line..we have connected parallel Ncc T0 with T3. in this prob, shount’t be OCC T7 along with NCC T4 ,instead of T3 (as Northen red will be red after T4 and remains till T7 )??
    2) in same n/w , Q0.2(west-red), you have connected Ncc T2 parallel with Occ T5,, shoun’t it be occ T6 in series with Ncc T7,,instead of occ T5???
    I have these doubts….I hope u have understood what i’m tryinbg to sya
    I be waiting for doubt clearification. Thank you