NEEDING HELP WITH CIRCUIT

Discussion in 'General Electronics Chat' started by metalca, Oct 30, 2014.

  1. metalca

    Thread Starter New Member

    Sep 11, 2014
    16
    0
    HEY ALL IM NEW TO ELECTRONICS, I WANT TO MAKE A 9V CIRCUIT USING 10MM RED LEDS, IWANT TO USE 20 LEDS, JUST WONDERIND WHAT LEDS TO BUY AND AND WHAT RESISTORS I NEED AND HOW MANY, ANY HELP WOULD BE GREAT THANSK
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
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    Welcome.

    A minor suggestion: use lower case...

    Does 9V mean a battery or a plug-in power supply? If plug-in, what are its specs?

    Do you have a link to the specific LEDs you intend to use?
     
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,782
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    use the forward voltage rating of the LED (Vf=2.3) for example.
    guess.
    4 leds?
    4 x 2.3=9.2.
    too much!
    guess again.
    3 leds?
    3 x 2.3=6.9
    now subtract from your battery voltage.
    9 - 6.9=2.1 You have 2.1 volts left. set your current limit using that value. choosing a current limit of 15 ma.
    2.1 / .015 = 140 ohms for a current limit resistor.
    so your series string would have 3 leds, a 140 ohm resistor and would draw 15 ma of current. Just add more series strings of leds and resistors to increase the number of leds( in multiples of 3 in this case). current used by each parallel string is additive. for 21 leds you would draw 15 x 7 ma = 105 ma and your 9 volt battery would not last very long
     
  4. metalca

    Thread Starter New Member

    Sep 11, 2014
    16
    0
    possibly 16leds then im new to it all this is day one of learning lol. its a 9v battery the square type ones, leds im not sure what to get only red 10mm ones.ima paranormal investigator and im tryin to make a red illuminator not infrared just a red one but unsure of what parts to get
     
  5. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,782
    941
    find an led you like and get its DATA SHEET. the info you need to calculate with are in it. post a link to it or pdf of it here
     
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
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