FLASHLIGHT

OBJECTIVE

The objective of this project is to understand the principles of open and closed circuits and the basics of D.C. circuits.

SKILLS LEARNED

How to properly strip and prepare a wire for use.
How to solder.
How to construct a simple closed circuit.

TIME:     Four Hours

INSTRUCTOR NEEDS:

One instructor per five participants

PARTS LIST
One 1.1/2" P.V.C. extension tube w/nut
One 1.3/4" Rubber stopper
One Rotary switch
One 8" strip of metal repair tape
One 3" diameter circular piece of medium weight paper (similar to a manila envelope)
One Flashlight bulb Two "D" batteries
One 1' piece of 22 AWG magnet wire
One 1' piece of insulated connecting wire (22 AWG or smaller)

COST:     $10.00

TOOLS AND SUPPLIES
Wire stripper/cutter
Soldering iron
Solder
Sandpaper
Scissors
Needle-Nose pliers
Hack saw/file

ASSEMBLY PROCEDURE

  1. Provide each participant with the supplies and equipment listed above. Caution: The soldering irons are very Hot!

  2. Use the Hack saw or file to cut a groove running the length of the extension tube inside the tube. Note: If a hack saw is used it will be necessary to remove the blade and then replace it after inserting it through the tube. This groove will be used to accommodate the negative lead wire, so it should be deep enough to allow the batteries to be placed in the tube while the lead is in it. Caution: Do not cut or file all of the way through the tube!

  3. The tube should be constructed so that one end has a flange with threads for receiving the nut. It is on this end, between the beginning of the flange and the threads that a hole should be drilled to accommodate the rotary switch. After the hole is drilled the switch should be mounted. One lead of the switch should lay in the groove and exit the end opposite of the threads and the other should exit out the end with the treads. The leads to the switch may need to be extended by soldering longer wires to them.

  4. Two springs should now be made using the magnet wire. One should be small enough to fit inside the tube in the end opposite of the thread (negative end). The other should be just wide enough to allow the light bulb to fit inside, but still touch the spring. It should be just long enough to extend by one coil past the base of the bulb. Each spring needs to be sanded on an inch of its surface at one end to remove the insulating lacquer. The builder should be careful though to remember which end is the sanded one.

  5. Using the soldering iron each spring needs to be tinned on the sanded region. This is done by first applying a small amount of solder to the iron, touching the iron to the spring until the spring is hot and then applying a small bead of solder to the spring. After this is accomplished the same needs to be done to the leads of the switch mounted earlier. Once all of the wires have been properly tinned, the negative lead can be soldered to the spring made for the negative end of the tube and the lead on the thread (positive) end of the tube can be soldered to the spring made to fit the light bulb. Since a solder bead exists on the spring, to solder the wires to the springs it is only necessary to remelt the bead and push the wire through it while keeping the iron on the bead.

  6. Now that the basic wiring is complete, now the simple optics can be made. Take the metal repair tape and cover one side of the circular piece of paper. This will act as a reflector for the light bulb. Using a pair of scissors, make two cuts approximately 1/2" apart in the reflector paper. These cuts should begin at the edge and go to the center of the paper and should look as if a piece of pie has just been removed. Now bring the two edges of the paper together to form a cone. This should fit inside of the nut. If it is too wide overlap the edges of the even more until it does fit and use some of the left over repair tape to temporarily secure the cone on the back of the paper. Note: Do not press too hard on the securing tape so that it can be removed later.

  7. Place the batteries in the tube with the positive pole toward the threads. Make sure that they are pushed together inside of the tube so that a good connection is made and then place the spring on the negative end on the battery so that the soldered part is touching the negative pole of the battery. Then press the stopper over the negative end of the tube. It will be a snug fit, but it will go on. If it is too difficult some filing may be necessary.

  8. The trickiest part of this project is fitting the reflector paper to the tube with the batteries and the light bulb inside. With the reflector cone intact, cut a small amount off of the tip with the scissors. This forms a hole which should just be big enough to allow the light bulb to fit though from the back (non-metallic) side.Caution: Please remove only very small amounts (1/16") at a time until the light bulb fits. Once the light bulb is in place, place the spring on the stem of the bulb so that the soldered end is closest to the glass end of the light bulb. Then place this assembly inside of the nut and then attempt (do not force) to screw the nut onto the threads. If it does not fit because of the length of the reflector, disassemble it and trim a small amount from the outer edge of the paper then reassemble the flashlight and test again for fit. This should be done repeatedly until the nut is able to thread onto the tube and the stem of the light bulb is allowed to comfortably rest on the positive terminal of the battery while protruding through the hole of the retlector.

  9. Now turn the rotary switch and there should be light. If not, check the following:

      10. Are the batteries good and touching each other?
      Is the switch in the "on" position?
      Is the light bulb touching the positive pole of the battery and are the springs making good contact with the bulb and the battery?

North Carolina 4-H Electric Energy Lessons     ER- 21