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 NXP Semiconductors


  • Traffic Light Controller using Johnson Decade Counter

  • Created: Mar 13, 2014

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Description

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Summary

A traffic light is a set of electrical colored lights placed at intersections and crossroads to direct vehicular traffic and control the flow of traffic. Typically the light signals are as follow: red for stop, green for go and yellow or amber warning light for proceed with caution.


Oscillator U5 drives a 74HC4017N divide-by-ten counter. The first output of U1 appears at pin 3 that supplies a positive voltage to U2, a MOC3010 optocoupler/triac-driver IC, turning it and triac TR1 ON that lights I1, which is the red lamp. The second output appears at pin 2 and passes through D1 to the second MOC3010, U3, thereby lighting the yellow lamp, I2. The third output at pin 4 turns ON U4 and the green lamp, I3. The fourth output at pin 7 travels through D2 and into U3 to light the yellow lamp, I2, again.


If you would like the traffic-light system to follow the normal sequence of green, yellow, and red, make the following circuit changes: Disconnect pins 10 and 15 of U1 from each other. Remove D1 and D2 and connect pin 2 of U1 to pin 1 of U3, then connect pins 7 and 15 of U1 together. Use U2 to drive I3 (the green light) and U4 for I1 (the red light).


This circuit can be used to control traffic in public places or to demonstrate traffic rules in traffic parks. This will ensure that traffic moves as smoothly and safely as possible and for the protection of pedestrians crossing the roads.