PLC02: Traffic Lights

A Programmable Logic Controller, or PLC, can be used to control any process that requires automation, such as processes found in a chemical plant, automated machinery, or laboratory equipment. When used in such a process, the PLC is programmed to perform a set of logical steps in a specific order to complete the desired task. These steps are programmed into the PLC using a ladder logic program, which consists of a specific set of instructions which will be used to define the process and control the machine.

This PLC experiment allows traffic light control of crossroads using a timed sequence. The control program can be developed to cope with interrupts from pedestrian crossing requests or off-peak vehicle detector inputs.