Most flashlights are of no use if their batteries are dead. But you can build a flashlight that doesn’t need batteries, by harnessing the electrical power generated from a magnet passing through an electrical coil. This power will light an LED and provide light that is always available when you need it. All you need are a few parts from a hobby store, some household tools and an hour or two.
Spread newspaper on a table, and place a small sheet of cardboard on it. Take the lid off a 35mm plastic film canister, and trace a circle around the canister onto the cardboard. Trace another circle around the canister on another section of the cardboard.
Put the lid of your plastic film canister on top of one of the circles. Trace a circle around the lid. Repeat the procedure with the other circle that you drew. Cut the outer circles from the cardboard, using a utility knife, then cut along the inner circles to create cardboard bands.
Push one of the cardboard bands down over the top of your film canister until it is almost at the bottom. Apply white glue to the side of the film canister where it touches the cardboard, so it adheres. Do the same with the second cardboard band, but place it only a quarter of the way down the canister's sides.
Place one end of the 30-gauge enameled copper wire along the top of the bottom circle. Leave a tail of wire about 8 inches long. Wrap the wire continuously around the canister, moving up from the bottom circle until you come to the top circle, and then going back down again. Do this until you have wrapped it around the area between the two circles at least 200 times.
Cut off the end of the wire, using wire cutters, leaving about 3 extra inches. Strip 1/2 inch of insulation off from the ends of the wires that are at the top and at the bottom of your film canister.
Make a small hole in the lid with a utility knife, and push your LED into the hole from the inside of the lid, so it peeks out.
Solder one of the wires that have been stripped of insulation to one of the two contact pins at the bottom of the LED. Solder the other wire to the other contact pin of the LED. Make a small notch in the side of the lid with the utility knife.
Push the wires through the notch in the lid, and put the lid on the film canister. Wrap a strip of cellophane tape around the wires that are wrapped around the film canister to secure them in place.
Open the lid of the film canister, and insert two neodymium magnets into the canister so they are free to move. Put the lid back on.
Shake the film canister to cause the magnets to move back and forth and generate electricity to light up the LED.