Soldering Can Be Simple and Easy
If you're willing to undertake this small project, by the time you are done you will feel confident enough to pick up a soldering iron whenever the need arises. Soldering is not difficult if you follow a few common guidelines and I'd like to offer a couple of important tips. I've been involved with electronics and soldering for a long time and believe I can make you feel comfortable with it very quickly.
Use a soldering tip that is a good size for the work you are doing. A temperature of 700 degrees Fahrenheit is about right if you have any choice.
Use only 60%tin/40%lead solder, and a small enough diameter to let you regulate its application and flow easily.
If you get too much solder on a wire, simply swipe it away with the tip, letting the tip collect it. For larger items, such as the brass tube, heat the solder until it s liquid and then quickly move it to the edge of a wastebasket (or other safe place) and tap it gently. The solder will fly off. You have to be fast before it cools. Be careful doing this. Protect or avert your eyes. Another thing you can try is wiping away excessive liquid solder with a wet paper towel. The solder is hot, so if you try this, watch where it goes. Keep it in the paper towel or let it drop somewhere safe. For difficult solder removal, there are suction devices, called solder pullers, which will remove hot liquid solder from a connection.
There can't be ANY movement in a soldered connection until it cools and hardens. Usually three to five seconds. If there is, it will be a bad solder connection. It may be dull and may come apart. Reheat it and let it cool without movement. Look for a more smooth and shiny appearance.
Tip#1 - Use a damp sponge to wipe the tip before each connection that you solder.
A clean tip transfers heat much better. Make it a habit to pick up the iron, wipe both sides of the tip, then continue on to your soldering. Dedicate a small sponge as part of your soldering kit. Keep it just damp, gently squeezed out. It will get dirty and collect old solder. It will sizzle when you clean the tip. That's normal.
Tip#2 - Use the iron to heat your work. Let the work melt the solder.
Metal must be up to a certain temperature for the solder to "wet" the metal and bond to it. Flowing hot solder onto colder metal creates what are called "cold solder" connections. Solder, on cold metal, behaves like water drops on a waxed surface. It won't adhere.
Do more than "touch" your work with the soldering tip. Slight pressure will help the heat to flow. If two items are being soldered, try to find a corner or "V" where you can place the tip to heat both items at the same time.
Items with little mass, such as wires, heat and cool more quickly. And the heat will travel through them more quickly. Items with more mass, such as a brass tube, will take longer to heat up and longer to cool down.
With these things in mind, you're ready to start soldering.
Tinning the Resistor
Get the soldering iron warmed up and have solder ready. And a sponge. I suggest a small piece of wood to solder on. It doesn't pull heat out of what you're soldering. And, little burn marks let you know you're soldering at a good temperature.
(Tinning the resistor)
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Place the resistor on the wood. Place the soldering iron tip at the end of the resistor's wire, pressing gently. Apply the solder to the wire slightly above the tip. Let the solder flow onto the wire. As soon as it does, take the iron away. Let it cool. You should have a blob of solder firmly adhering to the wire. It should look fairly shiny. You can re-heat it a second time if you need.
(Resistor after tinning)
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When satisfied, do the other end too.
As you're doing this, try to think how the heat flows. You heated the end of the wire. Heat traveled up the wire, past the place you soldered, but also beyond, into whatever component is further up the wire. That's why you don't want to apply heat for any longer than necessary.
A resistor is a good component to learn with because they're designed to get warm and dissipate heat. If you think you need more practice, cut a 1/2 inch or so off each end of the resistor and try it again.
Tinning the LED
Tinning the LED will be much like the resistor, but you want to get it done without taking too long. LEDs are more heat sensitive. You'll be OK if you don't have the iron on it for a long time. Probably no more than a couple of seconds, less time if you can.
(Tinning the LED)
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Do both wire leads. You can separate them a bit to make it easier if you want.
Below is a picture of what the results of your tinning the resistor and the LED.
(Both LED and resistor tinned)
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Transformer
Remove the connector by clipping it from the end of the transformer's cord and discard it. Split the two wires apart for a few inches. Strip and twist the ends of the wires.
(Transformer with stripped wires)
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With the wires stripped, tin them too, like you did with the resistor and LED. The wire is very long so you don't have any heat concerns.
Tack Soldering the Parts Together
To be sure everything works, and to give some tack soldering practice, we will temporarily tack solder the parts together.
Place the resistor and the LONGER wire of the LED together, parallel and overlapping a quarter inch or so. If you have trouble and want to tape down or lay something on the components, that's OK. Anything's fair.
Only a brief moment with the iron should cause the solder on the two wires to melt together. Do not move them at all until the solder is cool. As before, it should look fairly shiny. If there was movement during cooling, the solder may look dull and the connection may even crumble. Re-do anything you're not certain of, allowing cooling between tries.
(Tacking LED and resistor together)
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When the resistor and LED are together, it will make a convenient test device for what we need to do next.
Schematic Diagram
(Light probe schematic)
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Above is a schematic diagram of the light probe circuit. We are going to tack together the essential parts, without the brass tube, just to be sure they work.
First off, we need to determine the polarity of the transformer wires. We can do this by trial and error, using what was just put together. We know that the short lead and flat side of the LED is negative(-). A unique feature of LEDs is that they don't care if you connect them backward. They simply don't work.
Connection points:
Opposite end of the resistor from the LED (+)
Short LED lead (-)
DON'T CONNECT ANYTHING to the LED/resistor soldered connection.
You may want to tack solder the wires. Crosswise tacking is sometimes easier, and works for temporary purposes just as well.
You can also touch the wires to the LED and resistor by hand, to get them right before you tack solder. The isolated 12 volts is completely safe to do this with, even with the transformer plugged in. Just don't let the transformer wires touch each other.
With the wires connected one way or the other, it should work. When you find it, mark the wire connected to the resistor as (+). No need to mark both wires, but the wire connected to the short lead of the LED is (-).
(Light probe component test)
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Soldering Brass Is Fun
If you've made it this far, you have proven that you have the right parts and that they work together. And you've proven that you can solder. Next post we'll get the parts fitted and soldered into the brass tube and the light probe will be finished.
When you see how easy brass material is to solder, you may think of other craftsy kinds of things to do with it.
More soon...
John