Hello I’m just a beginner and I made a simple circuit with a resistor and a capacitor with a led in between.

As I understand the capacitor just accumulates the energy but why is my led not going on?

When I get rid of the capacitor and simply connect the cable directly to minus it all works.

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  • 1
    \$\begingroup\$ What is your plan with the capacitor? If it is ment to be a bypass cap then you need to put it between supply and GND. In your circuit the led will be on only a very short time (untill the cap is charged). If you just want to light up the led then i recommend to just remove the cap because you actually dont need a bypass cap. \$\endgroup\$
    – Jogitech
    Jan 14, 2019 at 13:43
  • \$\begingroup\$ @Jogitech I wanted to produce oscillations in my circuit. And I thought I could do it using a capacitor or am I wrong? \$\endgroup\$ Jan 14, 2019 at 14:14
  • \$\begingroup\$ Why don't you program the arduino to make the LED flash, just turn the GPIO on and off repeatedly? \$\endgroup\$
    – HandyHowie
    Jan 14, 2019 at 14:19
  • \$\begingroup\$ @HandyHowie because i'm intrested to make it work through the simple components to understand it better \$\endgroup\$ Jan 14, 2019 at 15:55
  • \$\begingroup\$ @DmitryParanyushkin To achieve oscillation, you need to have at least one source of gain in your circuit. This could be anything from a vacuum tube to a MOSFET or even something exotic like a tunnel diode. I would recommend the simple two-transistor two-capacitor astable oscillator, which you should be able to find schematics for online easily. \$\endgroup\$
    – Hearth
    Jan 15, 2019 at 17:34

1 Answer 1


A capacitor acts like an open switch when it is charged under dc condition. This cause zero current in the circuit if it is series with the LED and resistor and therefore the LED won't light.

When you remove the capacitor from the circuit, the current can flow and the LED turns on. That's it.

  • \$\begingroup\$ Ah ok is there a way to cause oscillations using a capacitor? What could I do or add to make it work? \$\endgroup\$ Jan 14, 2019 at 14:13
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    \$\begingroup\$ There are a lot of LED Oscillation circuit in the net. You can simply find one that you like by searching the keyword "Flashing LED Circuit". \$\endgroup\$ Jan 14, 2019 at 14:17
  • \$\begingroup\$ The phrase "when it is charged" doesn't really mean anything. The correct statement is that a capacitor acts like an open circuit under dc conditions. \$\endgroup\$ Jan 14, 2019 at 15:32
  • \$\begingroup\$ a capacitor is like a rechargeable battery, by itself it wont oscillate. but you can make an oscillator circuit as mentioned there are a ton of them out there. basically you use some form of switch when the cap charges to a certain amount the switch turns off, then some load starts to drain the charge in the cap, when that drops below a certain amount you turn the switch back on. the cap plus some load/resistance creates a delay, hysteresis. what you have done here create an open circuit by using the cap. \$\endgroup\$
    – old_timer
    Jan 14, 2019 at 15:56

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