I love LED's. They are my favorite electronic to work with. So today, my new instructable is on LED's.
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Step 1: Get Some LED's!
But you may ask, "What LED should I buy? There are too many too choose from!" Well, for beginners, it would be best to get some simple 3, 5, 8, or 10mm LED's. If you are going to buy LED's, buy them in bulk. They are much cheaper that way. LED's come in many different colors, from infrared, to ultraviolet, and many different shapes, from domes to boxes. Each LED has a voltage rating. Usually the whites, blues, greens, and violet/UV's are 2.8-3.3v. The yellows, reds, oranges, and some greens are 1.7-2.2v. For current, estimate it to 20 mA.
Step 2: LED Basics
Now before we start getting into lighting them up, we need to get to know them more. First of all, LED's have polarity, which means the + and - signs matter now. Look at the pictures with an incandescent bulb in them. You can see that it lights up no matter which way the current flows. But look at the LED. It lights if the current flows from the + side to the - side, but if you place an LED the wrong way on a circuit, it won't light, and if you push too much current the wrong way, you can burn out the LED. You can tell which side is positive (the anode) on most LED's by looking for the longer wire. Also, the negative side (the cathode) has a flat edge. Another thing is that an LED is a diode. A regular diode keeps the current flowing in one direction without affecting the circuit. As an LED is also a diode, A circuit with just an LED will be the same thing as a short circuit, pushing too much current through the LED and burning it out. Therefore, we need something to keep too much current from flowing through the LED: a device called a current limiting resistor, or resistor for short. But you may also ask, "But there are many resistors on the market! Which kind should I use?" Never fear! You can figure out the resistor you need with any power source (NO MAINS POWER!!!) and any LED using your computer, or this website. The formula for calculating the resistor to use is R=(V1-V2)/I. R=resistance. The parentheses mean this is to be done first. V1=the source voltage. V2=the LED voltage. I=the current, which you should estimate to 0.02.
Step 3: Building a Circuit
Now that you know how the LED functions, it is time to build a circuit. To make a circuit, you will need LED's of different colors, 2AA batteries and holder, 10Ω and 100Ω resistors. For the ~3 volt LED's, use a 1-10Ω resistor, and for the ~2 volt LED's, use a 50-100Ω resistor. Follow the GIF to build the circuit. If the LED doesn't light up, turn it around. If it still doesn't light up, check your connections. If it still doesn't work, check the batteries. If they are fine, the LED or the battery holder is faulty. If it does light up, congratulations! Now see this instructable on LED throwies to put your LED's to use.