Instructables
This instructable will show you how to build a LED flashlight.
 
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Step 1: Tools and materials needed

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Tools
Soldering Iron
Hot Glue gun
Nail clippers
Wire strippers
Marker

Materials
1/2" Pipe Cap
4.5" x 1/2" Threaded Pipe
1/2" to 3/4" Pipe adapter
Perforated circuit board
Spring
Wire
Solder
Hot glue sticks
10 5mm LEDs
Sheet of foam
Shears or Dremel with cutting wheel

Step 2: Cut the perforated circuit board

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Cut a circle out of the perforated circuit board that will fit inside the pipe adapter.

Step 3: Dry fit the LEDs

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Put the LEDs into your circular circuit board to see how they fit.  Then trim the LED leads and leave the longer lead slightly longer.

Step 4: Solder the LEDs

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First solder the LEDs to the circuit board.  Then solder all the positive and all the negative LED leads together.  Test your LED board with a 3 volt power source to make sure you have soldered the LEDs correctly.

Step 5: Create a spring

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Create a spring for the flashlight.

Step 6:

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Screw your LED board into the steel adapter.  Leave an uninsulated wire connected to the negative connection of the LED board hanging so it makes contact with the steel adapter when screwed in.

Test your connections.  If it is working properly make a contact with a washer and some solder.  Fill the area behind the contact with hot glue.

Step 7:

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Cut some foam spacers that go between the battery and the contact point.  The spacers create a switch that is on when the adapter is tightened.

Step 8:

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Tweak the number of foam spacers so that the flashlight turns on only when the adapter is tightened.