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Simple Traffic Light
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The traffic lights, we see can be designed around an inexpensive ICs and enables us to understand the function of traffic lights in simple way. Simple Traffic Light kit is very much helpful for children to understand and follow the traffic rules.About the Circuit : The popular timer IC 555 and a decade counter 4017 makes the traffic light circuit as detailed here.IC555 is used in astable mode. It generates rectangular wave signal with variable cycle time. The output is fed to decoded decade counter 4017.This gives one pulse of timing for every cycle counted. Output of 555 is fed to CP0 input, which is sensitive to LOW to HIGH transition. CP1 input Pin 13 is tied to LO and is thus inhibited. The Last output Q9 (pin 11) is tied to reset input 15. The first counter output Q1 goes Hi at the first LO to Hi transition from 555 and stays Hi for one period of 555 clock. At next Lo to Hi transition, next output Q2 goes Hi. Similarly, all outputs go Hi subsequently one after another at each LO to Hi transition. Thus, outputs go Hi in each cycle serially from Q1 – Q9 and Q0. In our circuit here, 9 outputs are used. First four are connected together and drives a Red LED D9. This LED represents NO Go signal for four periods of 555 clock. Next output (Pin 10) drives Yellow LED which represents idle signal between RED and Green. This lasts only for one clock cycle i.e. ¼ th of earlier NO GO. Next four outputs similarly are paralleled and drive Green LED, which signals GO signal for the traffic. Last output is not used here. However, this can be used for another idle period which will make it complete. It is left for the user hobbyist to use and experience.
