R3l0ad

Ok, so I'm not the smartest guy in the world, but I don't think I'm retarded, and I just want somebody to verify this. I am in the process of building a new case for my carpc. (http://www.mp3car.com/vbulletin/showthread.php?t=19858) anyways I'm installing some LED's into them right now and I'm going to use one of the 5V lines from the floppy power connector... now I screwed up earlier and just connected and LED directly to it.. thus burning it out. Now what I think I need to do is just go down to radio shack and pick up a 3V resistor.... am I right? just solder the 3V resister between the hotwire and the (+) portion of the LED?

Let me know thanx in advance

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Ricky327

3V resistor? nonono.

What you need is to limit the current going into the LED. You can do this by adding a resistor in series with the LED.

Heres a typical setup :

2V voltage drop on LED (depending on colour/type)
15mA current to pass (depending how bright you want, dont exceed the limit)
5V supply

Check the datasheet for accurate values.

(5-2) / 0.015 = 220 ohms (the nearest E12 series)

The colour code (RED/RED/BROWN/GOLD) +-5% tolerance.

So put a 220 ohms 1/4 watts resistor in series with the LED...observe the A/K polarity of the LED, the flat side goes on the negative side of the supply.

You can get a 5V LED...probably easier for you

R3l0ad

Any idea where? I've looked locally and all the LED's I've found online thus far are maxed out at 3V. by the way thanks for the quick response!!

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New CarPC on the way again I think. I miss my old one!!!

Ricky327

Dont know in US but Ill give you a UK site :

http://www.maplin.co.uk/products/mod...737&Products=2

The 3V LED you are talking about is the forward voltage, thats not the supply voltage. Any LED can be made to operate at any voltage (within reason) by adding the series resistor.

jol

www.lsdiodes.com has leds, bright ones too. and almost free shipping!

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Ricky327

Cant see 5V LED in there jol

Confused

Check out the LED calculator, which will tell you what size resistor you will need for the LED and supply voltage


Garry

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cvi

Connect two LEDs in series and connect it to the 5v supply. Thats the easiest way to do it without resistors. The leds should be same specs to use this, but you dont need resistors.

cvi

crosseye

CVI, first of all, why would you connect two LEDs in series? Resistors are WAY cheaper than LEDs. Also, connecting a resistor in series with an LED is just as easy as connecting two LEDs in series.

Second of all, as far as I know, connecting two LEDs in series is not going to do anything to protect either LED. Kirchoff's Current Law implies that the current is the same through any number of components in the same loop (in this case, both LEDs in series). With two LEDs in series there is no significant impedence to limit the current. The only thing that's going to happen is the voltage drop across both LEDs is going to be equal to the sum of voltage drops across both LEDs in series.

My recommendation, throw a 230ohm-1Kohm resistor in series with the LED. If the brightness is not suitable, reduce the value of the resistor to increase brightness in the LED.

Ricky327

Wait up guys, this is getting to complicated now


Ive already done the hard bits, even show whats the colour code of the resistor should be and even explain how to connect it all up, it cant be any easier than that

SjLucky

yea it can
it could be done for you...

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heat

http://superbrightleds.com/

As the name implies, they have very bright LEDs

--Dima

Sh0cker

since we are talking about LEDs here, i need some help locating online store that carries 3mm Red(high bright) 12V LEDs.
thx

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cvi

Sorry, i wont speak up again. BUT...
* He needs more leds connected. (read post)
* He asked for a 3 Volt resistor.
Since there are no such thing, the easiest to do are leds in serial. Power coming from the computer psu would give 5V, that makes 2,5 V for each led.
* He dont have to mess with calculators or make a fool of himself asking for a 3 Volt resistor.
* It will work.

Jackso

I'm sorry to say, it won't work. An LED when conducting does not drop 2.5 volts. LEDs are misleading. They are CURRENT SPECIFIC not Voltage specific. The resistors aren't really used to reduce the voltage, they are used to limit the current. An LED will operate just fine with only 0.7 volts applied. The Spec on the LED of 3V is a MAX operating voltage, not a voltage requirement. Use the reistors. Or, if you wish, some LEDs are "pre-resistorized" to run TTL (5V) levels without an external resistor.

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