I am a beginner so bear with me.

I have attempted to design an LED flasher circuit but it gives unexpected behaviour.



When I apply the 9V DC voltage, the LED stays on for about half a second then turns off and will not turn on again until I discharge the capacitor.

Do you know what is wrong with my circuit?

The resistor value is correct for the LED at 9V DC.

  • 3
    \$\begingroup\$ A very warm welcome to the site. Unfortunately, the circuit is design is fundamentally flawed. It's behaving correctly but it cannot do what you want it to do. The site's a Q&A site, not a discussion forum, so it can't be for personal tutorial. Instead, search the internet for LED flashing circuits or similar, you'll find lots of well-written examples, explanations and diagrams already there for you. You can make better progress that way. Please do edit your question (not in comments, please) to explain whether you've built this circuit or are just simulating it. Again, welcome. \$\endgroup\$
    – TonyM
    Apr 3, 2022 at 9:07
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    \$\begingroup\$ There is nothing wrong with your circuit, it does what it should. What makes you think that the LED would flash? \$\endgroup\$
    – Velvet
    Apr 3, 2022 at 9:17
  • \$\begingroup\$ @noahburchell, The circuit you want to build is called a relaxation oscillator. There are many ways to build one. The answer from aadipj, below, using a 555 timer chip is one of them. But personally, I never learned much by playing with 555s. I knew how to wire them up to make LEDs flash, but that was it. I didn't start learning much until I built circuits like the "comparator based" one in the Wikipedia article that I linked above. \$\endgroup\$ Apr 3, 2022 at 14:24
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    \$\begingroup\$ @SolomonSlow, that's not the engineering approach. The OPs circuit clearly behaves correctly, by definition: its observed behaviour matches the expected behaviour. Therefore parts, assembly, power etc are all good. The problem is that the circuit design does not meet the requirements. These are important and clear concepts to understand, for efficient, simpler engineering development, used whether you're a complete beginner or are 40 years in doing a moon lander. OP is trying by learning, which is brilliant to see. Knowing these distinctions greatly simplifies learning, especially in practice. \$\endgroup\$
    – TonyM
    Apr 3, 2022 at 16:34
  • \$\begingroup\$ Hmm. Seems weird to me, but I've never actually designed circuits for a living so, Comment withdrawn. \$\endgroup\$ Apr 3, 2022 at 17:20

1 Answer 1


This circuit will not work as a flasher circuit. Try using a 555 timer in astable mode as shown here: https://elonics.org/adjustable-led-flasher-using-555-timer/


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