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I've been messing around with electronics lately and I wanted to make a simple circuit that lights up an LED when a capacitor is fully charged. I know that something could be done with a diode or something like this! Who could help me?

P.S. Does anyone know the minimum Farads that are needed to have a spark with a capacitor? and it is better to link them in series or in parallel.

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  • \$\begingroup\$ What is the voltage you are charging the capacitor to and what size is the capacitor (uF)? \$\endgroup\$ Sep 16, 2014 at 12:03
  • \$\begingroup\$ I honestly cannot believe you just asked the things you asked in the "P.S" part. Srsly. Go away. \$\endgroup\$
    – KyranF
    Sep 16, 2014 at 12:11
  • \$\begingroup\$ its a 9 volt battery and the capacitor is 3300uF but i have other capacitors.. thats why i asked (evetually i'd need more uF) if it was better to link them in series or parallel \$\endgroup\$ Sep 16, 2014 at 12:11
  • \$\begingroup\$ Capacitors become worse when put in series. If you want more "uF" you put them in parallel. \$\endgroup\$
    – KyranF
    Sep 16, 2014 at 12:28

1 Answer 1

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Yes, it can be done with a diode or something.

enter image description here

But you will need a few other components. R1 limits the charging current to C1 AND also limits the current taken from the battery when you short out the capacitor. Z1 (a 6V zener diode) will not conduct until there is a 6V across it. The LED also needs about 2.5V to turn on leaving about 0.5V across R2 which acts as a current limiter to the zener/LED circuit. With the values given the LED current will be about 10mA when turned ON.

It will give a spark when the output terminals of the capacitor are shorted. Beware of vaporised metal/burn hazard.

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  • \$\begingroup\$ Thank you very much but.. is it good to use a "PH4148" diode? And to use a 9 volt led? \$\endgroup\$ Sep 16, 2014 at 12:29
  • \$\begingroup\$ @Antoniod'Aniello the 4148 diode is just a small signal type, so no. The 9V LED is most probably just an ordinary LED with a built in series resistor so again I would say no. Use a zener diode (400mW or 1W type @ 6V) and an ordinary red LED. \$\endgroup\$ Sep 16, 2014 at 12:34
  • \$\begingroup\$ Oh Ok! Thank you again :) that's been very helpful \$\endgroup\$ Sep 16, 2014 at 12:37

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