I'll do this in more than one installment, starting with the parts needed. I've put a lot of information here about the parts and their electrical operation, just for completeness if anyone needs it. Don't let it scare you into thinking this is complicated. It's not. Just skip over what you don't need or aren't interested in.
It is my hope in posting this that it can provide some experience with soldering. There will be an example of soldering to a piece of metal (the brass tube), which will absorb and radiate heat a little differently than wires do. It will involve tinning of wires and tack soldering techniques. We will start by tacking the parts together to make sure they work. This gives an opportunity to do a few connections that are only temporary, allowing you to get the feel of soldering before the final assembly.
Brass Tube
The brass tube used was obtained from Ace Hardware, although it might be obtained from a hobby shop or a home improvement center as well. It is 7/16 inch in diameter and 12 inches long. It was priced at $1.99. I have included a scan of the label that came on it.
(Brass Tubing Label)
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LED
LEDs are fascinating devices. At their heart is a tiny semiconductor chip, maybe the size of a large grain of salt, and only a thin slice of that used. The chip is mounted into a reflective cavity, not unlike the inner surface of a headlight assembly. The mounting absorbs and conducts heat away from the chip. A hair fine wire connects the top surface of the semiconductor chip to the other terminal. Heat from the glowing chip is then conducted down the negative or short lead, and out of the LED. A diagram of a typical LED is shown below.
(LED Diagram)
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LEDs now come in several colors. There have been red and green for decades, allowing both of these colors as well as yellow, by combining red and green. Years later in the nineties, the process for manufacturing blue LEDs was perfected. Finally, with the three primary colors available, white light became possible by combining all three colors.
You want a WHITE LED for this application. I have posted a scan of the LED package here, since it lists several useful pieces of information. It was obtained at Radio Shack and was priced at $2.49. You get 2 LEDs in the package. Hopefully you can find a Radio Shack near you that carries this exact item. If not, you may need to substitute something else, noting the information you find on the package.
(LED Package - Front and Back)
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LEDs of this particular style usually have a flat spot on one side of them and have one lead that is shorter. Both should be on the same side. The short lead is the negative (-) terminal. The other lead (longer) is positive (+). The 7000 mcd specification is the relative amount of light the LED is designed to emit. You want this to be as high as possible for a good amount of brightness. The 25 mA specification is critical to the correct operation of the LED. Too little current won't light the LED very brightly. Too much current will burn it out. We want to get as close as we can to the recommended amount of current, which will be determined by a resistor (coming up). The FW voltage is what would be measured across the LED during proper operation at the rated 25 mA.
Transformer
We obtained the transformer from a local thrift store. You can see it still has the label on it. Look for one that is 12 volts DC. You may want one that is as small as possible. Any 12 volt DC transformer above 25 mA will do. We paid 99 cents for this one.
(Transformer)
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Resistor
A resistor is used to limit the current that the LED draws. If it were a larger value (more ohms), less current would flow and the LED would not be as bright. If it were a lower value (fewer ohms), more current would flow and the LED would shine more brightly, perhaps overheating and burning out. The resistor is calculated to allow the specified 25 mA of current to flow when 12 volts DC is applied.
The value of the resistor used here is 560 ohms. This can be determined from the colored bands around it. With the colored bands toward the left, the bands should be green, blue, brown. If there is a fourth band, ignore it. In the color code scheme, the first two bands are digits, green for 5 and blue for 6. The third band is a multiplier, or an easier way to think of it is the number of zeros you add. Brown is 1, so add one zero. A 5 and 6 with one zero is 560 ohms.
Resistors come in different wattages, too. The higher the wattage, the larger a resistor is physically, the more heat it can dissipate and the more current it is able to carry without overheating. This resistor is an 1/8 watt size, small enough for it to fit inside the brass tube.
(Resistor)
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Almost any departures from the LED and transformer used here can be made up for by changing the value of the resistor. You might want to be sure you can get this particular LED and a 12 volt DC transformer before getting the resistor. Any variations you need or want to make will require a resistor having a different number of ohms, that's all.
More soon...
John