I have read a lot of LED instructables and read many of the comments...I'm frightened by the number of people who still buy standard 5mm LEDs for $1+ each at local brick and mortar shops! I'm also shocked at the general lack of understanding for series and parallel circuits. But the good news is, there are people out there that can help, and I hope to make things simple and give you sources for great parts, cheap!
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Step 1: Where Should You Buy LEDs?
At the places with cheapest and highest quality LEDs of course!
Over the years, I have amassed this list of online retailers that have provided excellent products for literally pennies on the dollar over brick and mortar electronics providers. Some people like to use ebay, and they may be fine, but I can vouch for these sources as I have ordered from all of them, no duds, no funny color variations, no rusty leads, etc.
For basic, 3mm, 5mm, 10mm, round, discrete LEDs:
Average price for 3mm-5mm is $7-12 / 100 or 7-12 cents each!
Pros: They also carry the larger LEDs, RGB, bi-color, etc and a boat load of other cool gadgets. The best part? FREE SHIPPING on top of the great prices.
Con: Slow shipping, expect to wait ~1 month for your order to arrive.
Average price for 3mm-5mm is 3-7 cents each!
Pros: They carry an excellent source of LEDs and resistors as well as most other components you could possibly need: resistors/ICs/Pots/switches/sensors/bread boards/circuit boards/oscillators/etc.
Cons: Almost not a con: shipping is not free, but very cheap and usually arrives in 2 weeks or less.
For high power LEDs, 1 Watt plus:
Price for 1W discrete LEDs: 20-100 for $3-10
Pros: They offer a wide range of LEDs and color temperatures, some as high as 100W! They also sell power supplies, LED drivers, heatsinks, and a ton of other gadgets. They also have FREE shipping on orders over $15. As a bonus, if you live in the US, and the product you want is available on DXSoul, you might be able to get the items even faster!
Cons: Possibly slow shipping depending on what you order and where you live.
Step 2: Basic Tools and Materials
Here are some things that are invaluable to LED projects:
At least one bread board. You should ALWAYS test your circuit BEFORE you solder all your components! I cannot stress this enough, you will save yourself a lot of time and headaches this way. You should also have a good supply of jumper wires to use on said bread board.
You will need a good soldering iron as well, preferably one with temperature control. This will make your projects go so very much smoother. Also find a solder that you find flows well for you. Personally I cannot stand the newer 'lead free' variants and stick with the 50/50 blend of Pb/Sn (clean your hands after handling and don't lick your circuits...you'll be fine).
At least one 'helping hands' is also a requirement, as well as some small needle nose pliers, wire cutters, etc.
And don't forget the multimeter/voltmeter.
When it comes to connecting LEDs and circuits, you can buy 18-22ga wire, or find some old USB cables, video cables, or even ethernet cables then strip off the external casing and harvest the ~20ga wires (4 in USB, 8 in ethernet).
For heat sinks, if you are buying the higher power LEDs I recommend checking DX above, or for larger projects, look for a local metal supplier. My local shop sold me two 24" x 2" x 0.25" solid Al bars for $14. You will also need a good thermal epoxy or some other way to transfer the heat from the LED to the heat sink.
Step 3: Basics of Circuits
Here I'll keep it basic, but enough information to build simple LED circuits. All Images are screen caps of ledcalc.com this is a great website for determining the optimal resistors to use.
When wiring LEDs, its important that they are receiving the correct voltage and current, to do this the circuit usually needs a 'current limiting resistor' the easiest way to determine what resistance you need is to use an online LED resistor calculator. These will ask for your input voltage, the desired forward voltage across the LED, and the current that the LED will draw. It will then tell you what resistance you require, as well as what power rating you will need: low power LEDs typically are fine with 1/8 watt resistors, 1W + LEDs typically need 1/2 to 1 watt resistors since they run at 320mA or so.
1) Series Circuits - These circuits are suitable for hooking up multiple LEDs to a higher voltage power source, where the LEDs are DEPENDENT with respect to each other (See Image 1). This means that if one LED dies, the others will follow shortly (but if you wire it correctly, that shouldn't happen for 50k-100k hours!) The best situation for this configuration follows: If you have a 12V power supply, and you want to use (3) 5mm white/blue LEDs, wiring them in series gives you a total voltage drop of (3 x 3.2V = 9.6V) then a single resistor will be required to take up the remaining 2.4V, the resistor calculators will help with this as well.
2) Parallel Circuits - These circuits allow multiple LEDs to be hooked up to the same power source, but are INDEPENDENT with respect to each other (See Image 2). In other words, if one LED were to die in a Parallel-only circuit....all the rest will continue to function. This is also the best way to wire different LED colors, since they have different forward voltage requirements, and will require different resistors to achieve long life and optimal brightness. In this case, R1 will not be the same for both LEDs, for instance red LEDs use about 2.4V where blue is 3.2V, so the resistors will not match. Technically, the pictured circuits are BOTH series and parallel, since the LEDs are in series with the resistors, but they ARE parallel to each other.
3) Mixed Circuits - The most common application (See Image 3). Most projects will call for more than 3 LEDs, and the most common project power source is 12V, so most of my projects are both series AND parallel circuits. For instance, my DIY aquarium hood has 24W of 1W white LEDs run off a 12V source. That means I had to wire each set of 3 in series with a resistor, then multiply that by 8 (1W x 3)x 8 pair = 24 Total Watts.
I hope this guide will help you understand LED circuits, and give you the information needed to obtain hundreds of LEDs for all your projects! Best of luck!