Instrumentation and Control Lab
Ex 9: Traffic Light Control Using PLC
(i) Automatic control of traffic light using programmable logic controller
(i) Traffic light kit (ii) Mitsubishi PLC
(Ladder diagram should be drawn before coming to lab)
(i) In our country from night 8 PM to morning 8 AM onwards there is no traffic control. Only
yellow or amber lights blink across the crossing. Write a ladder diagram so that south and west amber
light blink at an interval of 1 second. The pedestrian crossing should be red always.
(ii) Let us consider there is only a road along north south direction (No east west road). So
there are two traffic signal poles, one for cars and another for pedestrians. Pedestrian can push a
button while crossing the road. If there is no interrupt from pedestrian the traffic light for car will be
green. When the crossing request comes the green light will becomes amber then red and then after
one second the pedestrian red light becomes green. It remains green for 10 second after that the
crossing becomes red. The road light becomes green after one second.
(iii) In an automatic traffic light control the south signal will be green for 30 second while the
west signal will be red. Next after 30 second the south signal will be amber then red (one second
interval). After one second the west signal will be green. It will be green for 30 second and after that
the signal will be amber and then red. It will continue in a cyclic way. Al the time the pedestrian
signal will be red (pedestrian will cross the road at their own risk (Indian style)
(iv) In an automatic traffic light control, if the car is detected the corresponding signal will be
green and the other crossing signal will be amber then red. If there is any pedestrian crossing request
the road light will be red and the pedestrian light will be green for 10 second. In the mean time the
west road traffic will be on. After 10 second the pedestrian light will be red and the road light will be
as per detected vehicles.