Written for beginners by a beginner. This project is my first project using LEDs, and I have documented it to present it to the world. I mounted two green LEDs in a sign that I could hang in my bathroom to solve certain...ahem..."problems."
Step 1: Materials
This is the list of parts I used in my project. All electronic parts were bought from Radioshack. If you can stand to wait, order some parts online. Radioshack has an absurd markup price. I went there because I'm an impatient teenager, and I wanted to do the project NOW. I am using a potentiometer because i wanted to be able to dim the LED, and a switch to turn it on and off.
-A two pack of green LEDs (part number 276-304)
-a SPST (single pole, single throw) toggle switch (part number 275-612)
-a 10 ohm resistor. I just had this lying around.
-3 AA batteries
-a 5K audiotaper Potentiometer (part number 271-1720)
-random pieces of wire that I had lying around.
-an "aquired" sign.
-a soldering iron
Step 2: Drilling
Step one is to drill holes for the switch and the dimmer pot. 1/4" for the switch, and 5/16" for the pot.
Step 3: Making the Battery Pack
I forgot to buy a battery holder, so insead of having to drive back to Radioshack to buy one, I just soldered three batteries together and duct taped them together. If you feel like it though, go ahead and buy a holder, and skip this step.
This is simple, just solder the "+" end of the battery to the "-" end of the other. It should be labeled on the battery which end is which, but if not, the flat end is the negative side, and the side with the little bump is the positive end.
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.
Step 5: More LED Requirements
another little quirk about LEDs is that they are directional, meaning that they only allow electricity to go one way. So we have to be sure that the current is flowing in the right direction. When the LEDs come out of the pack, the longer leg is the positive side. But, we can also figure out which side is which by looking at the LED close up. the bigger side is "-", and the smaller side is "+". (see notes on picture)
Step 6: Mounting the Hardware
mount the pot and the switch, and affix the battery pack to the sign (I used superglue)
Step 7: Its All About the Connections
run the wire from the positive terminal of the battery pack to one of the metal posts on the switch (it doesnt matter which one) and solder it there.
Step 8: More Connections
now, solder a length of wire from the other post on the switch to the middle post of the potentiometer. After that, solder the resistor to one of the other posts of the potentiometer, and to the "+" lead of the first LED.
Step 9: Closing It Up.
next, solder a length of wire from the "-" lead of the 1st LED, to the "+" lead of the 2nd LED. Finally, solder anothe wire from the "-" lead of the 2nd LED to the "-" terminal of the battery pack. Now your done!
Step 10: Add a Knob for Looks, and Enjoy!
Cut off part of the potentiometer shaft (I used a dremel), and throw a knob of some kind on there. You dont even have to, it just makes it look nice.