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Old June 17, 2009, 01:53 PM
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Default Project: Don't Get Electricuted/Blow any Parts

I couldn't think of a project title and well both things in the current title hold true. What i am going to be doing is using LEDs that i purchased that have currently unknown tolerances.
http://www.dealextreme.com/details.dx/sku.9077


So my first plan of attack is to take an older system/PSU, use a spare molex connector that i have, cut it so i can get to the VCC (+5V) and GND connections. Then i am going to hook it up to a bread board with a couple of different resistors and multimeter hooked up in series so i can measure the current (better safe then sorry). Most LEDS have a 20mA threshold, and though i know that to get 10mA (dont need to go over the threshold) with a 5V source its only a 500 Ohm resistor, potentially using a 5k resistor to get it down further to around 1mA.

Once that is figured out, i am going to hook up a one, then a couple of the LEDs in parallel to see they will work/don't blow themselves or anything else. After that, i plan on implementing this into my new case:

NCIX.com - Buy Coolermaster CM 690 Mid Tower Black ATX Case 5X5.25 5X3.5INT No PS Front USB Sound Firewire & eSATA - RC-690-KKN1 In Canada

Upon looking into the case, i've figured i could put a couple putting downwards at the possible fan location, maybe some near the side/front panels depending on how bright they turn out to be off my PSU. Also thought i'd add in switch to the front or rear of the case to enable to turn them on/off incase they bug me sometimes.

I'll start taking some pictures once this thing gets underway which is now. go go project Don't Get Electricute/Blow any parts!
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Old June 17, 2009, 03:23 PM
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Ok....I have some advice.

#1. Don't buy unspec'd LED's , they are inferior in every way.

#2. Use the 3.3 Vdc line from yer PSU (orange wire ) it's closer to spec , some will even run with no resistors (green/blue usually).....

-------

Personally , I only buy Cree or Luxeon LED's for lighting.

CREE | LEDs for the LED Lighting Revolution

Luxeon LEDs By Color : Luxeon Star LEDs, High Power LED Products & Accessories

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Old June 17, 2009, 04:20 PM
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Actually, I am a Computer Engineering Technology graduate so I know my way around electronics. Even though it had no datasheet, i used the 5V rail, as well as knowing that the max current was 3A. Starting at safety currents i know for regular LEDs and working my way up, i have a nice bright LED without the larger costs of the people you linked.

Below is the Molex connector stripped exposed VCC and GND wires


Next picture is of the wires hooked to a bread board (the white thingy for you non-technical folks) and the other half you can see is leading to my back up computer and its PSU.


This is with 5V power source, 5.6K Ohm Resistor, current therefore is: 890uA.





This is with 5V power source, 1.0K Ohm Resistor, current therefore is: 5mA.



This is with 5V power source, 560 Ohm Resistor, current therefore is: 8.93mA.



This is with 5V power source, 100 Ohm Resistor, current therefore is: 50mA.




This is with 5V power source, 50 Ohm Resistor, current therefore is: 100mA.



This is with 5V power source, 10 Ohm Resistor, current therefore is: 500mA. This is where the LED was actually starting to get hot to the touch and i decided to bump it down back to the 50 Ohm resistor as to not create more heat in the case, or overly shorten the lifespan of the LED.

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Old June 17, 2009, 04:30 PM
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Nice breadboard....Everyone need one of those !!

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I have to correct you again tho.

When wiring LED's it's voltage thats important.....don't forget , they are diodes ,so peak forward voltage it the value you need.Current is a resultant factor.Exceed Vp and magic smoke comes out.

Red LED's have Vp of about 2.2 volts.......orange yellow is ~ 2.6 ish..... some greens and blues are 3.0 - 3.2.....depends on spec.

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Old June 17, 2009, 04:34 PM
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Quote:
Originally Posted by BrainEater View Post
Nice breadboard....Everyone need one of those !!

-----

I have to correct you again tho.

When wiring LED's it's voltage thats important.....don't forget , they are diodes ,so peak forward voltage it the value you need.Current is a resultant factor.Exceed Vp and magic smoke comes out.

Red LED's have Vp of about 2.2 volts.......orange yellow is ~ 2.6 ish..... some greens and blues are 3.0 - 3.2.....depends on spec.

Its actually not my breadboard, it was one of my classmates who he let me keep because he didn't want to take all the parts we had on it previously. And yeah, i know voltage is important as well, but typically a protective resistor such as the ones i am using allows me to limit the voltage and set the current. This hopefully is going to be a fun project, i think i may need to change it though since really, there was no magic smoke at all when i bumped it down to a 10 ohm resistor with the 5V power source.
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Old June 17, 2009, 04:38 PM
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And another little thing - remember that the LED has a voltage drop, so a circuit using the LED, a 50ohm resistor and 5V isn't going to give you 100mA, because only part of that 5V is being spent on the resistor. Break out the DMM and get some ballpart Vdrop boundaries for the LED, and use that to configure the rest of the circuit.

Edit: I'm honestly a little bit amazed that almost 0.5A didn't pop that LED.
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Old June 17, 2009, 04:47 PM
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Quote:
Originally Posted by MpG View Post
And another little thing - remember that the LED has a voltage drop, so a circuit using the LED, a 50ohm resistor and 5V isn't going to give you 100mA, because only part of that 5V is being spent on the resistor. Break out the DMM and get some ballpart Vdrop boundaries for the LED, and use that to configure the rest of the circuit.

Edit: I'm honestly a little bit amazed that almost 0.5A didn't pop that LED.
Again i know all this stuff, i was more saying the current that was going to the LED. Yeah i was really surprised just the LED was hot and didn't pop. I imagine if i wired it with a 0 Ohm resistor it would either pop, or get really hot and burn out quickly.
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Old June 18, 2009, 07:52 AM
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Project is on hold for a couple of days, getting laser eye surgery done today.
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Old June 18, 2009, 08:44 AM
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LOL.... if you alter those LED's enough, you might be able to do your own laser treatment! Save some cash! :)
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Old June 19, 2009, 11:55 AM
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Quote:
Originally Posted by Prof. Dr. Silver View Post
LOL.... if you alter those LED's enough, you might be able to do your own laser treatment! Save some cash! :)
I thought of that, unfortunately they use gas lasers :( BTW surgery so far is a success but i'm not going back into the project till i have non fuzzy vision, for safety reasons.
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