# Need help with led circuit

Discussion in 'The Projects Forum' started by grognak, Nov 2, 2015.

1. ### grognak Thread Starter New Member

Nov 2, 2015
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Hello everyone,

I am trying to figure out what I need to complete a project I am working on. I am trying to run 9 of these Leds http://www.amazon.com/gp/product/B0059H5YUK?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s01 from a AA battery pack for a prop I am making. I will also be adding a toggle switch. I was wondering if anyone could tell me if the resistors it comes with will work or if I will need other ones and If the system will be efficient enough to run for a little while. Im concerned that I will either burn up my leds or it will drain the batteries in 10 minutes. I know nothing about wiring leds and could really use some help designing an efficient wiring schematic so my prop will stay lit for a while. thank you everyone.

2. ### #12 Expert

Nov 30, 2010
16,703
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Nobody can tell without the resistance rating of the resistors and how much voltage you are going to apply.

3. ### grognak Thread Starter New Member

Nov 2, 2015
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ok, :/ Im pretty lost here but I think 2 AA batteries would be 3v correct? I know the resistors are 1/4 watt but don't know the ohms. is there any way you would be able to let me know what resistors I would need based off of 2 AAs and 9 of those leds? should I use something besides AAs?

4. ### Dodgydave AAC Fanatic!

Jun 22, 2012
5,154
772
Says 2v drop, probably 120 to 330 ohms resistors,

Last edited: Nov 2, 2015
5. ### mcgyvr AAC Fanatic!

Oct 15, 2009
4,791
976
They seem to be 100 ohm 2% (brown-black-black-black-red)
and the LEDs seem to be 2Vf
so (3V-2Vf)/100 = .01 Amps (or 10mA) which is perfect for long life..

So with 2 x AA batteries you need to make 9 strings of an LED and resistor in each string..

Like this.. note only 3 shown..

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6. ### grognak Thread Starter New Member

Nov 2, 2015
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thank you very much! I am still a little confused as to how to wire them together to the power supply. (sorry, this is my first electrical project and its all foreign to me) also, would the resistor go be fore the led on the positive leg or after the led on the negative? thanks again for your help.

7. ### mcgyvr AAC Fanatic!

Oct 15, 2009
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I updated my post to show a schematic... and the resistor could be before OR after the LED.. it doesn't matter..

Think of the resistor as a "water valve"... It doesn't matter where it goes as it "sets the pace (sets the current)" for the whole garden hose.. The water (current) can only flow as fast as the valve allows it in the whole circuit.

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8. ### grognak Thread Starter New Member

Nov 2, 2015
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just refreshed and saw the diagram you made. thank you so much! I think I can figure that out youre the best

9. ### grognak Thread Starter New Member

Nov 2, 2015
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if I wanted to add a toggle switch in line I would do it on the positive leg correct?

10. ### mcgyvr AAC Fanatic!

Oct 15, 2009
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That would be "recommended" but in this situation it really doesn't matter..
But its usually always safest to disconnect the "non-grounded" connection.

grognak likes this.

Nov 2, 2015
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Thank you!

12. ### grognak Thread Starter New Member

Nov 2, 2015
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out of curiosity, how bright do you think the leds will shine in this setup?

13. ### blocco a spirale AAC Fanatic!

Jun 18, 2008
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Compared to what? My guess is that they won't be as bright as the sun.

14. ### ian field Distinguished Member

Oct 27, 2012
4,447
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This might help:-

http://www.talkingelectronics.com/projects/30 LED Projects/30 LED Projects.html