# NEEDING HELP WITH CIRCUIT

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

1. ### metalca Thread Starter New Member

Sep 11, 2014
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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
5,451
1,071
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
4,165
1,121
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
4,165
1,121
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

Oct 2, 2009
5,451
1,071