This question gets asked every day in Answers and the Forums: What resistor do I use with my LEDs? So I've put together several different ways to figure it out.
Lets get right to it:
Each of the steps do the same thing. Step 1 is the simplest and we go downhill from there.
No mater what way you choose you must first know these three things:
- Supply voltage This is how much power you're putting into the circuit. Batteries and wall warts will have the output voltage printed on them somewhere. If you're using multiple batteries*, add the voltage together.
- LED Voltage Sometimes "Forward Voltage" but usually just abbreviated "V".
- LED Current Sometimes "Forward Current". This is listed in milliamps or "mA".
Both of these last two can be found on the packaging for your LEDs or on your supplier's web site. If they list a range ("20-30mA") pick a value in the middle (25 in this case). Here are some typical values, but use your own values to be sure you don't burn out your LEDs!:
Red LED: 2V 15mA
Green LED: 2.1V 20mA
Blue LED: 3.2V 25mA
While LED: 3.2V 25mA
Okay, lets get started!*
Batteries in series
. Introduction photo credits:LED photo by Luisanto.Resistor photo by oskay.