I built a project with the help of a breadboard diagram. Now I want to understand what this circuit does. How does this circuit work? I am looking for an analysis of this circuit diagram.

Circuit picture

  • \$\begingroup\$ Maybe this page will help: elprocus.com/ic-4017-pin-configuration-application \$\endgroup\$
    – ErikR
    Nov 6, 2022 at 0:54
  • \$\begingroup\$ Obiick - Hi, What have you done on this so far, to try to solve your own question? Did you download the datasheets for the two ICs and review the components connected directly to each IC, to understand how each of those "blocks" works? In other words, to avoid people repeating things you already know, please explain exactly where you are stuck, so readers can focus their answers there. Thanks. \$\endgroup\$
    – SamGibson
    Nov 6, 2022 at 1:05
  • \$\begingroup\$ Hello Sam, I am pretty new in these thing. I just wanted to know how this circuit is working. How its making the 10 by 10 reaction game work. \$\endgroup\$
    – Obiick
    Nov 6, 2022 at 1:23
  • \$\begingroup\$ Hello EricR, thanks I will check on this page \$\endgroup\$
    – Obiick
    Nov 6, 2022 at 1:23
  • \$\begingroup\$ @Obiick - Hi, "I just wanted to know how this circuit is working." Stack Exchange has different rules to typical internet forums. Please familiarise yourself with the tour & help center for more details. In the help center article "How do I ask a good question?" it explains, among other things: "Sharing your research helps everyone. Tell us what you found and why it didn’t meet your needs. This demonstrates that you’ve taken the time to try to help yourself, it saves us from reiterating obvious answers [...]" i.e. people asking questions are expected to research first. TY \$\endgroup\$
    – SamGibson
    Nov 6, 2022 at 1:57

1 Answer 1


IC1 is an astable multivibrator, producing a 26.6 Hz square wave on its pin 3, with approximately 60% duty cycle. It's a classic 555 circuit, and you can read more about how this works and the frequency calculation at Wikipedia page about the 555 timer chip

That will flash the LED L1, but probably too fast to see.

When S1 is pressed, this signal is applied to the clock input of the counter IC2. This is a CD4017 decade counter. This counts input pulses and makes one of its outputs high, thus lighting one of the LEDs on the right, L2 to L11. When it gets to 9, it goes back to 0.

It will behave somewhat as an electronic random number generator, choosing to light one of the LEDs depending on how long you press the switch for.

Just for completeness: R1, R2, C1 control the frequency and the duty cycle; C2, C3 decoupling; R3, R5 LED current limiting; R4 pull-down; Diagram wrongly says 4017 is a "BCD counter", but actually it's a decade counter.

  • \$\begingroup\$ Wow thanks a lot. I will save this on my note for my study about this circuit. \$\endgroup\$
    – Obiick
    Nov 6, 2022 at 1:26

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