I apologize for a very stupid question, I'm very beginner in electronics. I wanted to make a simple oscillator based on NE555P chips I ordered from local store, but struggling to make it work. I found an attached schematics in wikipedia and hooked it to my breadboard. I checked all connections many times, everything seems to be fine. Here is a circuit: schematics

I use the following values:

  • R1 68K
  • R2 10K (bit different from table in wikipedia here: https://en.wikipedia.org/wiki/555_timer_IC#Astable, they recommend 8.2K. Could it be a reason?)
  • Ceramic capacitor between Pin 5 and ground (labelled 103, so should be 10nf)
  • 10uf electrolytic capacitor, negative going towards ground.

As power supply, I use 12V wall wart and breadboard power supply, tried both 3.3v or 5v jumper there, power supply works for sure, tested it without connecting to this circuit. Also when I turn it on, LED on breadboard power supply look dim on 3.3v and not working at all on 5V, so looks like something shorted internally.Also tried to use another NE555P, same result. I tried to make it as clean as possible to see the board. Hope you can help me and point me out where I did stupid mistake.

Also tried to change polarity of LED and electrolytic capacitor, no results.

Here is my breadboard photo, hope everything is visible. Of course I tried with connected power supply, just took it outside to take photo :) Thanks a lot.

enter image description here

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    \$\begingroup\$ Can you show how you are connecting the led to the output? Are you using a current limiting resistor in series with it? \$\endgroup\$ Jul 31, 2021 at 8:56
  • \$\begingroup\$ Problem solved, I screwed up with power supply polarity... Current-limiting resistor is a good idea, will do it. thank you. \$\endgroup\$ Jul 31, 2021 at 9:49

1 Answer 1


You've got the polarities on your power supply swapped. The positive outputs of the PCB connect to the negative (blue) power strips on your breadboard and vice versa.

There's a chance you damaged your 555 timer IC's by doing this.

Rotate the breadboard 180 degrees versus the power PCB to correctly align the polarities.

I also can't see a current limiting resistor in series with the LED.

  • \$\begingroup\$ Yes, I did very stupid mistake, after fixing the polarity everything works, of course. Checked everything dozen of times, except polarity of power supply facepalm. NE555 still alive, fortunately, and thank you very much for pointing me out to install current limiting led. Good lesson to me is to check everything, really EVERYTHING. Really appreciate your help, have a nice day :) \$\endgroup\$ Jul 31, 2021 at 9:48

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