please help...

[grimxneko]

first off, im new to this site and also pretty new to electronics and stuff. with that said, i have a some questons...
ok, so the situation is: im planning on making a fairly large infrared light sorce to mount on my video camera for night shooting. it's going to be an array of 20 infrared LEDs consisting of two different kinds of LEDs (ten of these big bright ones (Here), and ten of these mediocre smaller ones **broken link removed**). also, im planning to use a 9V battery for the power sorce, and somehow i want to make the birghtness adjustable (like using a dimmer or something) along with an on/off switch. now, i set up a prototype kinda thing to see if the circuit would work and just to get a visual idea of what i want the final product to look like (Here). keeping in mind im a complete begginer, i dont quite grasp the concept of using resistors. so when i wired this all up, i simply left out any resistors. also, since this was just a test, i didn't solder anything yet. i just twisted the leads together like a twist tie. oh, and take note that i dont have a multimeter so i dont know anything about the specs or details of the LEDs themselves besides whatever the pages that i purchased them from said (in the first two links). soooooo here's where the problems come in....
-i first tried to wire all the LEDs up in a parallel circuit but i noticed each additional LED made the whole thing dimmer. everytime i added one, the whole thing would become less bright. i tried this with up to 5 LEDs and gave up, thinking that by the time i got to my goal of 20 the whole thing wouldn't light up.
-so next i tried a series circuit. it worked with a small strand of 5 LEDs so i went on to connect them all. when that was all done i hooked it up to the battery and none lit up. i was (and still am) very confused by this. i tried many times after that; checking the connections, checking the battery, checking the + and - leads, even checking every light for a dead one. this all yeilded to nothing but confusion and frustration. the results (when there actually were any) were varried as you can see here.
-also, i mentioned before that (assuming i get all this working right) i would like to have the option to control the brightness/ dimness of this. i really dont know how to do that (a variable resistor maybe?? idk), so that'd be nice to know too.

so, in summary, im simply asking HOW?? how exactly should i wire all this up?? any help would be greatly appreciated.

 

[vne147]

First off all, STOP hooking up the LEDs to a power source without resistors. You'll burn them out. You need to use resistors to limit the amount of current that flows through each LED otherwise it will exceed the LED's maximum current.

Second, the 5 LEDs in series won't work with a 9V source becasue each LED has a voltage drop across it of anywhere between 1.5 - 2V depending on the current going through it. When you place the LEDs in series, those voltage drops get added up and if they add up to more than the supply voltage, it no workie.

Third, that many high power LEDs will QUICKLY kill a 9V battery.

Fourth, you can get away with placing 3 or maybe 4 LEDs in series but no more. To calculate the resistor you'll need for each branch use the following formula:

R = V/I

V = Vsup - n*Vf

Vsup = supply voltage. 9V in your case
n = number of LEDs either 3 or 4
Vf = forward voltage of each LED which is 1.5 - 1.6V according to the ebay auction
I = current. This should not exceed the maximum allowed current. Once agian from the ebay auctions for the smaller LEDs 60 mA or .06A is the maximum continuos current. For the larger LEDs, 140 mA or .14 A.

You'll want to arrange the LEDs like this:



Understand?

Edit: sorry I forgot to explain the potentiometer. That is for brightness control. As you turn it it will further restrict the current going through the LEDs. Another note is that since the big LEDs and the small LEDs require different currents, you'll only want to place big in series with big and small in series with small.

 

[audioguru]

I pity the poor little overloaded 9V battery.

 

[grimxneko]

thanks for your response and help, it actually made things much clearer. im almost laughing at myself cause of my obvious mistakes and ignorance. so yea, i pretty much see what you're saying. but as for the schematic you provided... that kinda threw me off and raised a few questions. like what does the GND stand for, where does the battery go, why doess it appear to not be connected at the bottom (where the GND is), and why are the resistors at the bottom? now, those are all technical question, but what really caught my attention is that it doesn't seem to be set up according to my original design. i need to do two columns of the five smaller LEDs and two columns of the five larger LEDs. and it's not just a matter of preferance either; i only have 10 of the larger LEDs which i have to split in two so they'll fit in the case i already have. plus there's the fact that i cant mix the big and small ones when constructing the seperate columns in series. uh, sorry, i think im rambling... my point is: 4 columns of 5 in series, but your suggestion doesn't seem to match that (right?).

oh, and i also asked all the same questions on a differnt electronics forum site (just to get an optimal variety of answers), and i ended up attempting to design a schematic based off both your suggestion and others. so i came up with this. i guess just let me know if it's right or not, and what to improve on. again, thanks for your help.