I do amateur astronomy, and one of the tools is a red flashlight (If you turn on your white light and ruin your astronomy buddies night vision, he'll probably knock your block off). But with the popularity of the new white LED's, red LED flashlights, especially inexpensive squeeze lights, are getting hard to find. This instructable will show you how to make your own squeeze light so cheap and easy, you won't mind loaning them to you friends that forget to bring things back...
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Step 1: Gather the Parts
There are so few parts, this shouldn't take long at all.
1 empty film canister (if you've gone all digital, go down to the local developer or camera store, they just throw these things away).
1 9vlt battery (doesn't even need to be a new one, I've found that ones run down to 7vlts will still light the LED's. So go replace the ones in your smoke detector, and use the old ones in your light.)
4 red LED's (I've used everything from the dimmer red "indicator" ones to the clear "Super-Ultra Bright") just make sure they are all the same.
A piece of packing foam, sponge, or packing "Peanut", about the size of the battery and about half as thick.
Step 2: Gather the Tools
This list is about the same length as the parts, and not nearly as picky.
Soldering iron and solder
hobby knife or scissors
paper, pencil, black and red marker or crayon (sorry not shown, but I figure you know what one looks like)
double-sticky tape or glue
needle nose pliers
wire cutters (or nail clippers)
Step 3: Make a Paper Pattern
Press the piece of paper over the lid to make a circle pattern to cut out. Cut out the smaller inner circle. If you want to take the time to measure and draw a circle with a compass, go ahead, but I'm moving on....
Step 4: Insert the LED's
Poke the LED's through the paper near the edge, be sure to leave enough room between the LED's so they sit flat and not on top of each other. The holes should be in a nice curved single file line. Again if you want to measure, the distance between the leads is 0.1" and give yourself a little more space than that between the LED's.
Take the LED's out, glue or tape the paper into the lid, and then using the pre-punched holes and the stick pin, poke holes in the lid. I use a cloth covered mouse pad to poke into instead of my fingers.
After all the holes are made, insert the LED's. Make sure to keep the short leads all on the same side, the short lead is the negative side, and we are going to wire the LED's in series, one long to one short. Make sure the leads go through the paper on the inside, this will come in handy later.
Step 5: Solder the LED's Together.
cut the middle leads short (about an 1/8"- 3/16" long depending on how far apart the LED's are) you want them long enough to get good contact with its neighbor, but not too long that it shorts out on the next lead. DO NOT CUT THE 2 OUTER LEADS. leave these long to touch the battery posts. Sorry the picture of silver leads on the white paper didn't turn out well, so I tried to enhance it.
Put a touch of solder on the leads that are touching each other, make good solder joints, but don't get it too hot, or you'll melt the plastic and/or ruin the LED's. The paper helps protect the plastic from the heat, but make sure not to melt the edge, or it'll be hard to put the lid on.
While you are here, mark the shorter lead with a black marker , and the longer lead with a red marker (a "+" would be good too).
Step 6: Finishing Up
Cut a second circle the same size as the first, and punch or cut a couple holes where the battery terminals are. this piece helps insulate the leads from the metal battery case.
Bend the 2 long leads over, and then down against the lid. The loop at the end helps make better contact with the battery.
Cover this with the second disk you cut, making sure the leads are under the holes. Glue or tape this disk in place, and mark the battery terminals again. I like to use a dotted black line for the negative side, cause it kinda reminds me of the crimped negative terminal on the battery.
Cut the piece of foam to fit down one side of the battery, and then tape or glue it to the canister. Don't glue it to the battery, you might need to change it one day. Although the battery lasts for quite some time.
The foam piece keeps the battery from rattling around, and also from turning in the canister.
Step 7: Put on the Top and Test It Out.
Make sure to line up the top properly, and snap it in place. Push down in the middle, and it should light, If not, pull the top off, and pull the leads away from the top some. There is some fine tuning required to get the right amount of squeeze pressure without the light staying on all the time. If it still doesn't work pull out the battery and touch it to the leads, if that works go back to fine tuning the leads, if not, see if you labeled the leads wrong, it wont hurt to hook the battery up backwards, it just wont work. Other than that, check your solder joints again or make sure you didn't insert an LED backwards.