PLC traffic light
In the link below I've shared a traffic light project based on ladder logic and simulated with an S7 PLC. When the selector
I0.5 is ON the yellow light (output Q0.1-Q0.4) blinks and the pause can be setted by the instructions T41 and T42. By
switching OFF that selector the cycle starts. The green light is controlled by the outputs Q0.0 and Q0.3, while the red light
is controlled by the outputs Q0.2 and Q0.5. The input I0.1 or I0.2 can be connected to a photocell switch, in order to make
it work depending on the traffic conditions (note that the input which is not used must be on).
If you want your traffic light to work without photocell you have to keep ON the selector I0.0. The inputs I0.3 and I0.4 are
supposed to be connected to the walker request buttons. By switching ON the selector I0.5 the yellow light blinks once the cycle
is completed. The image shows the input-output setting, but the connections may be different depending on the PLC model. Take a
look at your PLC manual before you connect it.
Watch on Youtube
Ladder logic (pdf)