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led wiring question

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Old 06-08-03, 05:44 PM Thread Starter   #1

Join Date: Oct 2002
Location: Iowa

led wiring question

I am sure that people have covered this already, but I don't know a whole lot about wiring LED's and stuff, so here's my question:

I am going to do a mousepad mod, using a USB cable to supply power. I am probably going to use 4 LED's (or do you think i should use just 2?). The USB line is 5v, so should i use four 5v LED's? I would rather not mess with resistors because, as i said earlier, I don't know much when it comes to doing wiring. Is there anything special i need to do when doing this wiring?
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Old 06-08-03, 08:13 PM   #2

Join Date: Jun 2001
Location: Lugoff, SC have to hook them up in parallel, becuase if you do series, the voltages will add (actually the resistence, but...that makes for a higher potential difference required to light the LEDs). Parallel is + to + and - to -, series is + to - and - to +. (You prolly knew that, but I was unsure, its better to make it clear). Also, did you **** someone off in here? This is the third thread ive had to go in on becuase noone else answered your question? I know the people that read this before me knew the answer. Were here to help others people! cmon! I dont wanna see this form start to be like anot[H]er forum I know of.


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Old 06-08-03, 10:40 PM Thread Starter   #3

Join Date: Oct 2002
Location: Iowa

no, i dont think i've made anyone mad here. If i did, im sorry, i had no idea. Also, this is the first post i have put about this topic, i just didnt have time when i wrote it up to find those, i was getting ready to leave my house. Thanks for the info though. And what you are saying is that as long as i do it in parallel and they are all 5v, i should be fine, right?
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Old 06-16-03, 02:21 PM Thread Starter   #4

Join Date: Oct 2002
Location: Iowa

come on now, can't anyone answer this completely?
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Old 06-16-03, 02:27 PM   #5

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Join Date: Oct 2002
Location: Clemson, SC

yeah its the first and last pin in the usb plug... attach all the + sides to the lead attached to the first pin and all the - sides to the other lead connecting to the far right pin... if you use all 5v leds in parallel this way it will work fine *btw i just tested the current coming out of the usb with a 5v led and it was the proper brightness so no need to use resistors... didnt feel like pulling out the mulitmeter*
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Old 06-16-03, 04:34 PM   #6

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Join Date: Mar 2001
Location: The Netherlands

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You need to know the polarity of the LED(s):

I would get LED's with a large emitting angle (20 degrees is small, ~100 degrees is large, LED's with a small angle won't spread the light real well so you need more LED's to light up a certain surface) and high MCD (MCD=millicandela), Ultra bright LED's are ~5000MCD.

I also suggest you DO use a resistor (to limit the current), as the LED's can't give of much heat when they're glued inside the plexi/lexan, the heat will shorten their lifespan, and it's not that hard, if you can solder a wire to a LED you can also solder a resistor in series.

You need a resistor of about 10-50 Ohm** (1/2WATT should be fine).

**When using 5V LED's.

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Old 06-19-03, 10:31 AM   #7

Join Date: May 2002

KILLorBE has an excellent picture, I just have to add a few pionters:
Assuming that the big lump inside is ground is not correct in all instances.
What's not visible in KILLorBEs drawing is the flat side of a LED. That little ring that goes around the LED at the bottom of the plastic housing is flat on one side.

There are different LEDs out there. Some have builtin resistors making them operable at a specified voltage without more resistors. Those are RARE and seldom what modders look for.

Ordinary LEDs have an operating voltage of maybe 2.0V or 1.7 V or 3.6V or 4.2 V. In every case you need an resistor to make sure that the current stays on about 20 mA even if the supplying voltage (maybe5V) does a slight bump.

If you have JUST LEDs maybe 6 pcs of 2V LEDs connected in series making them chow exactly 12 V. Well, they work fine and dandy sucking 20mA at exactly 12V. If by chance the voltage should go up to 12.2 V you might burn all of them at an instant since they now get 500mA.

LEDs aren't linear like resistors I.E if you up the voltage by 10% you get 10% more current . LEDs have a sharp knee around their operating voltage. I.E a boost of 10% voltage around the operating voltage can give a currentboost of 1000%.

So, you can connect maybe 5 pcs of 2V LEDs in series (Sucking 10V) on a 12V line and use a resistor to eat the remaing 2V for stability.

Connecting 2 LEDs at 2V each sucking total of 4 volts on a 5V line is a bit hard. Might be difficult to find the exact resistor.
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