Lab 5 - Sequential Logic Control



Develop a PLC program that will control a miniature set of traffic lights. These lights will go through a normal sequence, but will have pedestrian cross walk buttons that will activate a cross walk signal when pressed. When done the student should understand the design and implementation of time dependent control circuits.


Pre-Lab: (due at the start of lab period)

1. Draw a state transition diagram for the traffic lights given the process description below.

2. Write the ladder logic model for the state transition diagrams.

3. Develop an exhaustive test table that will test all of the possible transition states for the traffic lights.


Process Description:

We want to develop a controller for a set of traffic lights that is at the cross of Main St. and a less used Cross Rd. The lights under two possible sequences as shown below. In the normal sequence the green for cross is shorter with no cross walk light. If a cross walk button is pushed while the Main light is green or yellow the Cross green light will be on longer with a walk sign.




SoftLogix processor

Output lights




1. The instructor will describe how to connect the PLC, power supply, buttons, etc at the beginning of the laboratory period. As a group you will connect the circuits. Components used will include push buttons and red/yellow/green output lights.

2. As a group, enter and test the ladder logic for pre-lab 2 and conduct tests in pre-lab 3. The instructor must check the performance.



1. Pre-lab and updated laboratory materials.



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