Beginner's Introduction to LED Wiring

This How-To will explain to you how to do LED wiring. It will explain where to find the parts you need, and how to assemble them. The basic outline is this: I use a standard UPS (Uninterruptable Power Source) to power LEDs which are positioned in strategic locations throughout the house. The lights can be turned on whenever you wish to save electricity. In the case of a power outage, the LEDs will continue to function for many weeks because they will be able to slowly draw from the stored power in the UPS (which is nothing more than a battery meant to temporarily power computers during power outages). A $100 UPS might be able to power a computer & monitor for 45 minutes, but with only LEDs, it could probably continue for months. As a temporary warning to this HowTo, I have not yet completely figured this out. I am still making a few assumptions which you might find to be unacceptable risk. Uncertain details are marked in red. If you value your LEDs greatly, I suggest you not use these directions until I have cleared up the questions.

LED Options

It'll be easiest to find any of the following LEDs: White, blue, green, aqua, red, orange, yellow, violet, ultra-violet, and infrared. Don't forget that UV probably isn't healthy for your eyes on the long term, and infrared isn't visible. My personal favorite color happens to be blue. The LEDs you buy online will usually have several important pieces of information written about them: Before you go out and purchase any high intensity LEDs, I recommend you get some cheap ones at RadioShack or (heaven forbid) Frys. Those two stores will also sell high intensity diodes, but Frys has a poor selection and high prices. If you insist on getting some ultrabright LEDs at frys, look for the ones that say "10 Candella" and/or "Warning! Do not stare at LED may injure eyes". They'll cost you around $2 USD at Frys, and $1.50 online. I'll let you benefit from my online searches for LED vendors. I have personally purchased from and been satisifed with the quality of the first two vendors in this list:

SuperBrightLEDs.com
LEDSupply.com
TheLEDlight.com
eLED.com
AllElectronics.com
hebeiltd.com.cn (great price, but major wholesale requirements)

You'll notice that all these vendors will charge more for shipping than they do three LEDs. With this in mind, I recommend you order in larger batches to save money.

Getting Started

To explain how the LED works, I'll point you to howstuffworks.com. For the purposes of this howto, you only need to know that there are two leads coming out of your LED. The one which is slightly longer than the other is known as the anode. The shorter is the cathode. Anode is (+) and cathode is (-). The longer lead must be facing the anode(+) of the circuit. Failing to do this will not do any damage in the currently discussed circuit, but may do so on later projects of yours. Check your LED package for the maximum backward voltage. Our first instict as children is to attach a wire from the (plus) end of the battery to the anode of the LED, and then another from the cathode to the (minus) side of the battery. This is almost correct, but still missing some details.

Let's first give an explanation of how your circuit will work in layman's terms. To start out on your first LED circuit, you will have one resisitor and three LEDs in series. 'In series' means that they're daisy chained. This is how we calculate this circuit:

( Source Voltage - LED Voltage Drop ) / Amps = OHMs
~~~~~~~~

Source Voltage = 12 volts 

Voltage Drop = 9.3 volts (3.1 typical for a blue or white LED)

Desired Current = 20 milliamps (again, a typical value)

~~~~~~~~
So the resistor we need is:  (12 - 9.3) / ( 20 / 1000 ) = 135 ohms


Crude drawing of your circuit

Power Source

For this first project, I've found that probably the most useful tool for this initial practice project is a switching-mode power adaptor (which can switch been different voltages -- including 12v). I found one made by GQ for $8.79USD. Be aware, however, that you'll definitely need a "Fluke" electrical measurement tool or similar to keep an eye on the actual output voltage. Cheaper models such as the BA-53 will usually produce a much higher voltage on circuits with minimal current draw. That said, with your LEDs safely protected from over-voltage, having and adaptor which can do 1.5, 3, 4.5, 6, 7.5, 9, and 12 volts is very convenient. Especially convenient are the models with a clip meant to be placed on a 9v battery. The anode and cathode are spaced far apart on these, and will be easy to work with.

Next, you'll want a resistor to fit this circuit you've just built. You'll probably find that there are no 135 ohm resistors. Just round up (as little as possible). If you're looking for a way to identify resistors which have been distanced from their original packaging, search for resistor color codes. The wattage of resistors refers to "how much juice they can drink." That is, their ability to turn electricity to heat. 1/2w can swallow more than 1/4w. For this project, 1/4w should be fine, but it is always safer to go higher if you're uncertain. Unlike the LEDs which must been wired into the circuit facing the correct direction (see above), common resisitors can face either way. For future projects involving higher voltages, the wattage used by your circuit (and minimum required resistor) can be calculated by multiplying the source voltage together with the current you're allowing through the circuit. This particular example can be expressed as: 12v * .02A = .24 watts. So as you see, a .25 watt resistor (1/4) is already cutting it close. It is of interest to note that your typical incandescent light bulb will run between 60 and 100 watts, while your three LEDs are bright enough to read by and consume a mere .24 watts!

As a final note, starting with less voltage than was calculated won't hurt anything. There's no reason not to start at 1.5v and slowly switch up toward 12. Hook this all up, and you shold be the proud owner of three brightly glowing LEDs. The circuit which you've just designed is known as a "series," which refers to the fact that all components are daisy-chained.

Expanding your Ability

Now, you might ask: "So what if I want 18 LEDs in an arry? Do I need enough voltage to power half of Los Angeles"? The answer, luckily, is NO. The alternative is to split up all those LEDs into several chains positioned in (the opposite of series) parallel. To sum that up, the wire comes off the anode(+), gets split into six wires which each go through a resistor, three LEDs, and then meet back up before collecting on the cathode(-). Your power adaptor will be putting out (20mA * 6) because of the six chains of LEDs, but voltage running through the whole thing will still only be 12 for reasons I cannot explain.

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Thank you to John C. for providing an explanation of how to calculate the wattage in my
example circuit. If others out there would like to contribute, I welcome your input!

(last updated February 02, 2004)