I have a problem with my traffic light circuit. I've made sure of the wiring and everything seems right but for some reason only the yellow LED is lit constantly without it flashing and the other 2 LEDs are not even working. It's my first circuit so I feel a bit lost.

Here are some pictures of my circuit:

I didn't use the 0.1uf

enter image description here

Here's the circuit diagram that I'm using: BTW I didn't use the 0.1uf since I didn't have any enter image description here

I've got it from this website here


After receiving your answers, I have corrected the breadboard errors. Now only the red LED is lit. Here are two new pictures:



  • \$\begingroup\$ I don't see where the red and green LEDs are connected to anything at all. Check your wiring. \$\endgroup\$
    – tcrosley
    Commented Apr 23, 2015 at 18:12
  • \$\begingroup\$ I somewhat have the feeling you should check how a breadboard is wired... \$\endgroup\$
    – PlasmaHH
    Commented Apr 23, 2015 at 18:19
  • \$\begingroup\$ What's up with the resistor connected to the green LED? Why does it loop back to itself? \$\endgroup\$
    – Greg d'Eon
    Commented Apr 23, 2015 at 18:20
  • \$\begingroup\$ There's no connection between the 'f' and 'g' rows on a normal breadboard. As such neither your red nor green LEDs are actually connected to anything. \$\endgroup\$
    – brhans
    Commented Apr 23, 2015 at 18:20
  • 1
    \$\begingroup\$ Give him/her a break, they did say it's their first circuit. In my opinion you should start out simpler, wire a diode to a button and then build from there. Doing that would have made finding out that the understanding of breadboard wiring is wrong and easier to fix. \$\endgroup\$ Commented Apr 23, 2015 at 18:47

3 Answers 3


It looks like you are misunderstanding the way a breadboard is wired internally. Check out this link for information.

Here is an image, taken from that link:


One issue you have, as an example, is the resistor connected to your green LED. Both leads are plugged into a single node, and therefore it doesn't act to bring power to your LED (or do anything at all).

To see what I mean, look at this next image. All the holes marked by the green line are connected, and the blue holes are also connected. However, there is no connection through the red line. The green and blue lines aren't connected to each other.



Regarding your modified circuit, the breadboard corrections look good. Here's what else I see:

  1. You'll need to connect all the power busses together (and the ground busses). Often, this simply requires putting a wire from the V+ rail on one side to the V+ rail on the other side, and again for the ground busses. However, as RJR points out (see his comment below) it appears that your breadboard has multiple power busses along each edge ("V3", "V4", etc). If these are, in fact, not connected to each other, then you'll have to do it with wires.

  2. The diode from pin1 of the 4017 appears backwards.

  3. You'll want to check the polarity of your LEDs. I can't tell from the pictures if they are oriented correctly.

Good luck!

  • \$\begingroup\$ I'm very new to all of this so thank you that was very helpful. \$\endgroup\$
    – Sarah_b
    Commented Apr 23, 2015 at 21:54
  • \$\begingroup\$ @Sarah_b Glad to help :) \$\endgroup\$
    – bitsmack
    Commented Apr 23, 2015 at 21:57
  • \$\begingroup\$ I've fixed the errors. I'm not sure if there's any other error but now only the red LED is lit. If you can take another look at my circuit I'd really appreciate it! Pic1 - Pic2 \$\endgroup\$
    – Sarah_b
    Commented Apr 23, 2015 at 23:15
  • \$\begingroup\$ @Sarah_b I added your new pictures to your original question, and have updated my answer. Good luck! \$\endgroup\$
    – bitsmack
    Commented Apr 23, 2015 at 23:46
  • \$\begingroup\$ Also note that the 'busses' at each end (labeled V1, V2 etc. form the looks of it) are not connected. At least it seems the holes with the red line are connected - so 1-14, 17-30, etc.). The black line leads me to believe that those holes are all connected though. Tip: get a cheapo multimeter and try it out! \$\endgroup\$
    – RJR
    Commented Apr 23, 2015 at 23:54

Take a look at this section of your first picture: -

enter image description here

Red and green LEDs are unconnected.


See the line that dips in the middle of the board that cuts of the two sides as such the resistor thats supposed to be connected to the RED LED is not since there is a gap between it extend the resistor over the gap OR move the LED up and connect a wire from the LED to the voltage rail (i think you connected it to 0v ?)


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