Traffic light Circuit

Discussion in 'The Projects Forum' started by daskywalker, Apr 19, 2010.

  1. daskywalker

    Thread Starter New Member

    Mar 28, 2010
    Here I am again, with the traffic light project I am constructing below:

    So now I have to write a detailed report on the role of each component in the diagram. I know the 555 timer provides the one-shot pulse and you can adjust the pulse duration with the capacitor and resistors. I am not sure why the transistors before the LEDs are there.
    I also know that the diodes act as some kind of logic gate. Anyone know how it affects the counting sequence of the LEDs?
    I guess the counting sequence of the 4017 counter is on their datasheet right?

    Next part. I was thinking about adding a switch so that when switched on both sets of lights will flash yellow ONLY. Do I need to add a separate counter for that or can I put the switch between the 555 timer and the decade counter, so that the 555 timer pulse goes straight to the yellow LEDs?

    Many thanks.
    Last edited: Apr 20, 2010
  2. Markd77

    Senior Member

    Sep 7, 2009
    Try here:
    The diodes are so it stays longer on one part of the cycle than the other. Search for diode OR gate.
    The transistors are acting as switches.
    Yes the 4017 datasheet will tell you what it does.
    You won't be able to flash the yellows with this circuit because the reds would also flash.