Working out resistors

[Blueprint]

Hi, i'm pretty new to circutry... anyway, im using a simple breadboard system, simply making an LED light up.

I'm using 3xAA batteries (4.5v), i have a LED, but just need to know what strength resistor to use.

Can anyone help?

Thanks.

 

[Someone Electro]

It depends on what kind of LED.We need to know the LEDs voltage and curent.

This is caculated this way:
(Vb-Vfw) / I = R

Vb = batery voltage
Vfw = LEDs voltage
I = curent
R = resistor you nead.

Easy as pie.

 

[Jay.slovak]

I think Microcontrolers is not a got section for resistor-for-LED problem :lol:

 

[Someone Electro]

yea that too.


unles he is trying to controll it from an mcu but i dont think he is doing that

 

[Blueprint]

Ok thanks guys... It's a bog standard 2mm LED, think its a 2v LED. how do i work out the current? (i'm not controlling it from a MCU yet...)

 

[Jay.slovak]

Ok thanks guys... It's a bog standard 2mm LED, think its a 2v LED. how do i work out the current? (i'm not controlling it from a MCU yet...)

OK, say you power it with 5V, then resistor needed (for LED U=2V, I=0.02A) is (5-2)/0.02=R, Therefore R= 150Ohms

Usually LEDs require 20mA (0.02A) current to function

It's that simple :lol:

 

[Blueprint]

You're a genuis thanks v much .

 

[Someone Electro]

(4,5 - 2) / 0,01 = 250 so that wod be an 220 Ohm resistor(it wod let 10mA in the LED)

This is Ohoms law whith a litle tweak to caculate this (Ohoms law wod be V / I = R).

 

[Jay.slovak]

You're a genuis thanks v much .

I wouldn't consider anybody as genius only because he/she can calculate proper resistor for LED. :lol:

 

[Blueprint]

Yeah true, but I found it pretty hard to work out the current of a 2mm LED from Maplin. Most of their stuff is German for a start, so it takes me a little longer to read their kinda 2-lined instruction leaflets that comes with the shizzle.

Anyway thanks for your help, you're all Ledges.