wich resistor to use

so i have my arduino mini running on 2x AA batteries

i wanne put 3 LED on digital output for blinking

wich resistor do i need for the leds

Red 1,8V-2,3V
Yellow 1,8V - 2,3V
Green 3,2V 3,4V

all 20ma

R = V / I, so with 3V, to get a 20mA current, you’ll need a 150 ohms resistor.

helmuteke: so i have my arduino mini running on 2x AA batteries

i wanne put 3 LED on digital output for blinking

wich resistor do i need for the leds

Red 1,8V-2,3V Yellow 1,8V - 2,3V Green 3,2V 3,4V

all 20ma

http://led.linear1.org/1led.wiz

i think the link is the correct one

so i need a resistor of 56ohm and 1ohm

is this correct because , the first replier said 150ohm

Since its an AA battery, any low value resistor will work, but that's not engineering!

An AA battery already has a very high internal resistance, which prevents it from achieving very high currents. That, by the way, is basically the difference between batteries and capacitors. I usually use no resistors with common 3mm and 5mm LEDs and CR2032 batteries, when testing the LEDs. That, however, is not the proper way to do it.

If you replace the AA batteries with a 3V power supply capable of higher currents (such as a wall wart), you'll fry your LEDs if you use anything smaller than 120 ohms (considering they have some tolerance to higher currents).

If you go with 1 ohm resistors, you might as well don't use any resistor and save the space and a few pennies.

With those currents, it is ok to use 1/8W resistors, but do yourself a favor and use 150 ohms resistors.

BTW, in the link posted, what was the forward voltage you used for the diodes (LEDs). You should use some value between 0.7 and 1.2V. With these numbers you'll find the resitor to be 120 ohms. Use 150 ohms just to be safe.

If you're running off a battery then maybe 15ma current will be OK. LEDs are easily bright enough to see at 15mA (or even less!) and your battery will last a lot longer.

i'd probably use a 3v zener or even a diode with 2aa's