Choosing the right Resistors

For led you need to know the max operating current and the voltage drop for led this nomaly comes with the leds you buy or on the site in the spec sheets for led

for example 5 - 3.4 / .020 (this is you input voltage 5v - 3.4 is the voltage drop / .020 is max current so works out like this 5-3.5/.020 = 80 means you need 80 ohms resistor

for more then one led can use a LED calculator work same way just work out for a lot led easily

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

http://www.hebeiltd.com.cn/?p=zz.led.resistor.calculator

http://www.dannyg.com/examples/res2/resistor.htm

http://www.csgnetwork.com/resistcolcalc.html