LED Beginner project: part 1

Step 4 OH NO, MATH!!!

Ok, now the boring part. LEDs are very sensitive to the amount of electicity flowing through them, and as such, we have to make sure the amount that is going into them is the specified amount. If we look on the package, we see that they require 2.1 volts, and they draw 30 milliamps. Now, because we are wiring the LEDs end to end, they are "in series," which means that their required voltage adds. SO, running two LEDs that require 2.1 volts means that you need at least 4.2 volts of power to run them. This is why we used three batteries (each battey is 1.5 volts...1.5 x 3 = 4.5 volts). Now, 4.5 volts IS pretty close to the required voltage of 4.2, but we dont want to take any chances of burning out the LEDs, so we have to use a resistor, which limits the amount of electricity going to the LEDs. So all we have to do, is figure out what kind of resistor we need. You CAN do the math to figure it out, using OHM's law, and I recommend that you a least understand the concept behind it, but luckily for us, there are tons of LED calculators on the internet. I used the one at http://metku.net/index.html?sect=view&n=1&path=mods/ledcalc/index_eng. So, in the "series" section of the page, we put in a supply voltage of 4.5 volts, a voltage drop of 2.1 (the required voltage of the LEDs) and the desired current of 30 milliamps. After hitting calculate, we find that the required resistance is 10 OHMs.

Comments

[stringteary]

here's the new url:
http://metku.net/index.html?path=mods/ledcalc/index_eng

[mr bkilled]

sorry to tell you this but the link that you posted has changed and that page does not exist anymore so you should think about changing it

[bustersdad]

Thanks for the info on the calculator. I have wanted to "play" with LEDs for a while but that math piece was getting in the way. With this information in hand I think I can do it. Thanks again!