# Resistors

I've always had a problem understanding resistors. Perhaps I just need to see an example, but until then, I'm completely stuck.

Say I have 3.3v of power with 40mA of current, and I want to power an LED that requires 2v and 20mA to run. What sort of resistor would I use to make sure I don't blow it out?

I know I can calculate the resistance of the two using Ohm's law, but is that what I'm supposed to do? Where do I go from there?

## Comment viewing options

One thing to avoid a little confusion:

- Most power sources provide a certain VOLTAGE

- The CURRENT depends on what you connect, and it's Resistance.

See the video tutorials at http://thenewboston.org/list.php?cat=41, videos 6 through 10 should be relevant to your question.  There is also a lot of programming video tutorials on this website!

you might want to check this out as well: http://www.allaboutcircuits.com/vol_1/chpt_2/1.html

For these kinds of things the thing you need is called 'Ohms law' and every roboteer should know it.
its a very simple forumla that describe how volts and amps and resistance relate to eachother.

its the basis for like 90% of all math in electronics.

This site is pretty cool.

Yeah there are some laws and math involved, but this is good also http://ledz.com/?p=zz.led.resistor.calculator

Everything you could ever want to know about this specific problem is here. Best LED tutorial ever.