Design ladder logic for Three way traffic light control system using Programmable Logic Controller PLC programming.
The traffic light is one of the classic examples in PLC ladder logic.
We can take three directions (North, South, west, and east) with three outputs (Green, Red, and Yellow) lamp as output.
You can build your own concept for making logic for this example or follow the below given conditions for the traffic light.
Following tabular column is the sample logic for the three-way traffic light,
Write the ladder logic for this 3-way traffic light control using the above sequence.
Inputs and Outputs
Three way Traffic Light Control
PLC Program Description:
Latching rung to operate the system through Master Start and Stop PB. 2.
RUNG 001 and RUNG 0002
Starting the timer to turn on first output West Green so east and west should be in red.
The Comparators in Parallel rung are used to turn off East red after 15 sec.
Timer T4:2 timing bit in parallel contact used to turn on East red again in 5th and 6Th Step. (Refer Above Tabular column for clarification)
Turning on North Red up to 3rd step using T4:0 and T4:1’s timer timing bit and comparator blocks.
Turn on East yellow for 5 sec using comparator blocks.(Step 2nd) 5.
The same procedures followed to turn on further outputs. ( Refer the above Tabular column for the sequence of operation)
Reset coil is turned on using T4:2 ‘s done bit to restart the cycle from beginning
Program runs continuously until STOP PB is pressed.
Also Read: 4-way Traffic Light Control
Training Course: Allen Bradley PLC Course