enter image description hereThere is a traffic light circuit that I have built shown above. It works on circuit wizard just as I want but when bread boarding both the astable and monostable work however my 4017 does not I have looked over and I am not sure what is wrong.


  • 2
    \$\begingroup\$ You are missing resistors to your LEDs for one. Unless your aim is destroying LEDs and Logic chips. \$\endgroup\$
    – Asmyldof
    Feb 6, 2017 at 18:05
  • \$\begingroup\$ I don't see any power supply bypass capacitors - you should have 0.1 uF capacitors between the supply and ground pins of each IC, close to the IC, and a small electrolytic cap (maybe 22 uF) between supply and ground somewhere on the board. \$\endgroup\$ Feb 6, 2017 at 18:24
  • \$\begingroup\$ A description of how you think your circuit is supposed to work would help a lot. \$\endgroup\$
    – jippie
    Feb 6, 2017 at 19:16
  • \$\begingroup\$ Thannks for the help so far and it is meant to run in the uk traffic light sequence of Red-Red+Amber-Green-Amber-Red \$\endgroup\$
    – user350574
    Feb 9, 2017 at 16:23

1 Answer 1


It looks like you have the Reset pin (pin 15) of the 4017 not connected to anything. It could be floating high (reset), low, or somewhere in between. You should connect it to ground. Or, perhaps you want to connect this reset to some signal that will reset / synchronize your counter when idle? As it stands, your the counter will start and stop at fairly random count states.

And why are your first few counter outputs not driving the LED circuits? I thought a traffic light needed to always have one light illuminated.

Also, the 4017 outputs may not provide enough current to light your LEDs. It looks like these pins can only source a couple of mA, and driving these LEDs and diodes without any series resistance may overload the outputs. Consider using buffer transistors to drive the LEDs.

  • \$\begingroup\$ Peter Bennett is right about the bypass capacitors. \$\endgroup\$ Feb 7, 2017 at 1:26
  • \$\begingroup\$ Thanks and also the first 4 pins are unused because my red LED has been connected to Q10 which allows it to automatically run through the first 5pins in the sequence without needing to be connected to them, allowing it to come on at the same time as the amber LED which has been connected to Q5 \$\endgroup\$
    – user350574
    Feb 9, 2017 at 16:25
  • 1
    \$\begingroup\$ Q10 (actually, /Q10) -- Yes, I see that now. I should have looked at the datasheet more carefully! \$\endgroup\$ Feb 9, 2017 at 19:31

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