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Old 2nd January, 2002, 02:35 AM
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Unhappy Resistor needed for LED

hi there !
hey...can anyone help?
I don't know how to calculate the ohm for da resistor.
here is the formula that i've found from websites:
Ohm = (Mains Voltage - LED Voltage) / LED Amperes

The LEDz i have is 3V but i don't know anything about the LED's ampere.......
the main voltage for this is 5V
Please help...thanks in advance!

ANDREW@METALFREAK

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Old 11th January, 2002, 09:50 PM
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As far as I've even done; LED's need a resistor only to slow down current so it doesn't go to infinity; as such the resistor you put in sets the amperage accordingly; just make sure it gets you down to 3V...
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Old 11th January, 2002, 10:13 PM
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Ok assuming aa average LED arround 20ma of current then you need a 250ohm resistor, i think been a while.

someone please check for me
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Old 11th January, 2002, 11:24 PM
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I was told by friends who knows electronic that the resistor to be use depends on the voltage rating of the LED you use. You best bet is to use a selected and fix it up there after use the multimeter to check the actual voltage that is going through the LED. If it is below the rated voltage you are OK, unless you want to make it brighter. Then you can change the resistor to a higher rating.

This are the guideline I've got for the 3.3 volts LED.

1) For 12 volts supply use 1 KOhm.
2) For 7 Volts supply use 300 Ohms
3) For 5 volts supply use 125 Ohms.

This resistor must be connected in series to the positive pole of the led, which usually is the longer lead.
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Old 12th January, 2002, 07:22 AM
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thanks
but i manage to connect them.....without using resistors...
thanks alot guys!
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Old 13th January, 2002, 05:49 PM
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Without resistor? The led will not be able to survive the voltage for long.
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Old 13th January, 2002, 06:16 PM
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If at all, at 5V they will be gone in a flash, but a nice bright one
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