I whipped up this little project from scratch as a means to teach my thirteen-year-old cousin how to solder about a month and a half ago. He did all of the soldering that you see in this instructable (and not bad at all! He's a natural!) He liked the flashlight so much that I think he still carries it around with him!
Step 1: The Parts
What you will need:
1) Hard plastic 9v battery clip
2) tactile switch (tact switch)
3) Jumbo LED or really bright LED, whichever you prefer
4) proper resistor(s) for your LED
5) 9 volt battery - duh
6) hot glue gun and cheapo soldering iron with solder
The battery clip, LED, and resistor(s) can all be purchased at RadioShack or some other similar electronics store. The tact switch came out of an old broken VCR - check some old junk electronics that have buttons that click, and you'll probably find some tact switches inside. However, you could buy them new from digikey.com or something like that if you wanted to. If you are going to get your tact switch out of something, though, you'll probably need to use a desoldering iron (or something similar) to remove it. A solder sucker works just as well.
Step 2: What LED to Use and What Resistor to Use
As many of you know, any time you ever use an LED you should have a resistor in front of it. How do we know which one to use? Well, you could be a nerd and do the calculations yourself or simply go to this website and have it done for you. Word on the street is that's what all the cool kids do.
Step 3: Throwing It All Together
The easiest way to go about this would be to hot glue the tact switch, LED, and resistor in place before messing with any solder. If you do this, then you can cut the wires to just the perfect length and your friends will be very impressed with your soldering prowess. Oh, and make sure you do the next steps WITHOUT the clip attached to the battery. Whew, that would have been a bad idea...
Use a wire stripper to strip just a little bit off of the ends of the wires (after you've cut them to the right length), dip them in flux (or lemon juice if you prefer), and tin the wires (put some solder on them so that they'll attach easier when you're making your connections). The flux (or lemon juice) will make the solder spread nice and evenly over the wire. Trust me, even first-timers can figure this out.
In case you're totally new to this, your LED will have two leads coming out of it - one will be longer than the other. That one's positive, the other's negative. Also, sometimes the plastic of the LED will be slightly flat on one side. That side's negative.
The rest follows pretty logically - connect the black wire to the negative lead of the LED. Connect the red wire to one of the four leads coming off of the tact switch. Connect the resistor to the lead that is diagonally across the switch from where you connected the red wire. Then connect the other end of the resistor to your LED. After checking to make sure you connected everything correctly, snip off the extra two leads on the tact switch that you didn't use.
Throw on some more hot glue to make sure everything holds, add some red tape because it just rocks so hard (or leave it naked, that works too), and you have just made yourself one heck-of-a great beginners project / LED flashlight!
Step 4: Closing Comments
The point of this lil' project is that if you're trying to teach someone or yourself how to solder, this is a great project that isn't particularly dangerous and there shouldn't be too large a chance for failure (unless you burn out your LED because you wanted to see if it works without the resistor... that's a no no). Also, it's a useful project for a rainy day for you electronics hobbyists who probably have all the necessary parts just laying around already (like I did).
Obviously, there are ways to modify this project such as adding a switch to make it stay on without having to press the button, but I say this setup encourages energy conservation! Yeah, that's it - it's efficient and will make your battery last longer! Plus, since you didn't mangle the battery any and the entire thing is housed on the hard plastic battery clip, you just switch out batteries when you need to.
One definite way to cut the cost of this project is if you're making several of these (say for a Boy Scout troop going on a backpacking trip?). Since many parts come in packages of more than just one item, then you might as well make a few while you're at it!
Thanks for reading and I hope I inspired at least someone to burn their fingers with hot glue in an effort to make something that's fun and kinda useful!