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Page history last edited by PBworks 17 years, 9 months ago


photos - http://flickr.com/photos/13559856@N00/sets/72157594177077815/

word doc - http://electricity.pbwiki.com/f/TEActivity%20shakeflash%20light.doc

LED flashlight - http://www.mindspring.com/~jeffpo/ledlite.htm

Rough Science Make a flashlight - http://www.pbs.org/weta/roughscience/discover/powerplant.html#flashlight

Zoom Sci flashlight - http://pbskids.org/zoom/activities/sci/flashlight.html

Shake battery - http://www.halfbakery.com/idea/Battery-Shaped_20Shake_20Generator

Shake generator - http://www.creative-science.org.uk/gensimple1.html

Amazing Magnets - http://www.amazingmagnets.com/index.asp?PageAction=VIEWPROD&ProdID=90

Shake to charge flashlight - http://www.discovercircuits.com/forums/ultimatebb.cgi?ubb=get_topic;f=6;t=000005;p=0

Inventor of the shake flashlight? - http://www.appliedinnotech.com/

Capacitor source - http://www.maxwell.com/

Night Star Physics guide - http://home.comcast.net/~dcforums/nightstar_pysicsguide.pdf

Scitoys - http://scitoys.com/

power amplifiers and rectifiers - http://www.angelfire.com/electronic/funwithtubes/Amp-Power_Supply-More_Info.html

Schematic symbols - http://www.electronics-lab.com/articles/basics/theory/schem.htm




Introduction / Motivation

[Suggest how the teacher might prepare the students for the activity. Provide an engineering context. How do you grab the students' interest? This could be a demo, an example or real-world context.]


Every time I go to use a flashlight, the batteries seem to be dead. When I went to the convenience store, they had one of those shake flashlights for sale on the counter. When I looked at the light, it seemed so simple, but I shelled out ten bucks for it anyway. It worked fine for a while, but then it seemed to stop lighting the led. Upon closer inspection, it appears that the wires had broken away from the circuit, so I got to thinking. How can you make your own shake flashlight? How does it work? Why does it have a magnet and a coil of wire instead of batteries? Why does it have four diodes arranged in a rectifier? What is a rectifier?


Show the students a shake flashlight and ask them if they know how it works. explain and show that a dc electric motor, when turned, generates electricity. You can put an led to wires attached to the contacts of the motor, then turn it. You may have to turn the motor quite fast, but it works. With an led, it will only work with the correctly polarized current, so try turning the motor both directions.


How much do batteries cost? What are the inconveniences of dead batteries? What are the environmental consequences of batteries? What are batteries made of and how do they work?


How is electricity generated? How is electricity generated in a nuclear power plant, coal fired or oil fired plant? (heat is used to create hot water, which turns to steam, which then is used to turn a turbine. When the turbine turns, it moves either a wire coil surrounded by a fixed set of magnets, or it moves the magnets surrounded by a wire coil. The action of the movement between the magnet and coil causes the electrons to be forced along the wire, which results in electric generation.


In the Shake flashlight, the magnet is moving inside the tube, and the coil is stationary around the tube. When the magnet moves, it forces the electrons along the wire. If the voltage is high enough, it can do the work to light the led. If the voltage is not high enough then the user will not see any effect.


Some variables to be aware of:

Magnets - Ceramic magnets are inexpensive, but they are not very powerful relative to neodynium. The more expensive 'rare earth' neodynium, or rare earth magnets are very powerful. They can be found for free by carefully taking apart old discarded computer hard drives. You should be able to find at least two good sized rare earth magnets inside. These can be carefully broken into smaller sections and sandwiched between the cheaper ceramic magnets to build a more effective low cost magnet. If you have ring magnets with holes in the center, you can add a steel nail or other iron based material to the center to increase the power of the magnets.


Magnet wire - Thinner wire with more turns is more effective than thicker wire with fewer turns. 28 guage wire will work, but you may have greater success with 32 guage. 28 is easier to handle, than 32, but 32 will be more effective in the generation. An effective way to measure and store the wire is to have students wrap the wire directly from the spool onto a 1 foot long stick or paint paddle. The wire will stay in place better if the ends of the sticks have notches. The wire will settle into the notch and not slip off the paddle. Students will need to wrap at least 300 feet of wire onto the paddle, which can take most of a period to wrap and store. Any part of the magnet wire that will be electrically connected to the circuit must be stripped of its insulation. Do this by either sanding the emulsion off or you can try using nail polish remover. Be very careful to only remove the insulation from the sections of the wire you need to be electrically connected.


Tubes - In our development of the project, we started by using a white board marker with its felt ink carrier removed. To do this, pull the end off the pen with a pair of needle nose pliers. The ink carrier should fall out. Be careful not to get the ink all over the place. Set it aside, you can cut it and use it for bumpers at the end of the magnet's run. If you want to remove the tip of the pen, you should be able to pull the tip with the pliers. Inside the tip area, there is probably a metal pin that held the felt tip in place. If you are going to put the led in the tip, you will have to bend the pin out of the way or otherwise remove it.


Another idea, maybe simpler, is to use pvc pipe. The pipe is cheap, and the ends are available at most hardware stores. If you buy from a home center or plumbing supply store, you should be able to get the parts pretty inexpensively. With pvc, you can use end caps and 90 degree elbows to form the flashlight. Put foam, packing peanuts or crumpled up plastic bags in the end caps to act as a cushion. Most shake flashlights have a spring or bumper to bounce the magnet at the end of its run. You can drill holes in the fittings of the pvc to allow the wire to pass from the outside where the coil is to the inside where the wire will meet up with any circuitry, such as a switch or a rectifier


Soldering - Use the thinnest solder you can get. Thicker solder requires higher temperatures, and students tend to use a lot of it. You may also find it helpful to keep the roll of solder out of sight, and hand out only a foot or so at a time. This will help keep waste to a minumum. You should be able to buy the solder in a 1 pound roll through a catalog. If you go local, you may only be able to find smaller quantities. A 1lb roll should last a very long time. Use a soldering iron stand, or at the very least, have students do all of their soldering on top of a piece of heavy carboard or thin plywood. If you don't do this, you will get burn marks on your tables, which will help you remember this project for a very long time. Solder is an alloy, usually with a rosin or acid core. Acid core solder is usually not reccomended for electronic circuitry, so stick to rosin core. One of the common components of the alloy is lead, which is known to cause learning disabilities in small children. Students should be careful not to inhale too much of the fumes, and they should wash their hands after working with solder. Solder containing lead should never be used on domestic plumbing. The solder used in plumbing has a high silver content. There are some lead free options available for soldering electrical components. Look into it when you do your supply research.


Soldering Technique - Sand any insulation from the wires you want to connect. You can use a nail file or sandpaper, finer grit paper will do less damage to the wire than coarse grit paper. You could also strip the insulation with the edge of a pair of scissors or a knife. Try it out and see what works.


Make a solid mechanical connection between the parts. Don't expect the solder to hold the joint together by itself. You should probably wrap the wire around the legs of any components such as leds, diodes or capacitors. If the wire is already holding on, the solder will just help it to stay in place and assist in the conduction of electricity.


Apply heat to the joint with the soldering iron. What is often effective is to place the iron below the wires to be soldered, and allow them to heat up. When the wires are hot, you may notice that they change colors slightly. Touch the solder to the wires to be connected, and the solder should flow through the joint. If you do it this way, you will not be likely to have a 'cold soldered joint' which will be less likely to conduct and may cause the circuit to fail. Try not to apply the solder directly to the tip of the iron. This will melt the solder, but it may not adhere to the components.


Allow the soldered joint to cool, and either do the next one or try it out.


If you have any suspect connections - Examine the connections visually first. You can also pull lightly on the connectors to see if they fall apart. Next, you can use a continuity tester. Most multimeters have a continuity setting, which beeps when the two probes are both touching the same conductor. If you do not get continuity through the circuit, then you will want to rexamine the soldering.


LEDs - Light Emitting Diodes are a semiconductor that allow current to pass in only one direction while they emit light. White and blue led's require a higher amount of voltage compared to red, yellow and greens. If you want your shakelight to use a white led, you will need around 4 volts. If you use one of the other colors, you can get away with a lower voltage. The strength of the magnet, the thinness of the wire and the number of turns are all factors in voltage level. You can get something to work easier by going with cheaper, lower voltage leds.



Vocabulary / Definitions (optional)


lines of force

tesla (unit of measurement)







[Clearly explain the actual procedure to follow to conduct the hands-on activity.]

Make two cardboard circles that will fit tightly around a 1 1/4 inch film canister. Using fine sand paper, sand 1 inch of insulation off of the magnet wire. Start turning the wire around the spool leaving 3 inches of wire on the sanded end. You will need to wind 500 – 1000 turns. After completing the turns sand 1 inch of insulation off the other end. Next solder each end of the LED to bare magnet wire. Place a magnet in the film canister and shake.

Measure out 300 ft of magnet wire

Neatly wrap the wire around the 4 inch lenth of PVC pipe.

Leave approximately 6 inches on each end of the coil outside the coil.

Once the coil is wound sand the insulation off each end of the magnet wire.

Drill a small hole in the underside of the 90 degree elbow.

If you are going to use a switch, drill some holes to wire the contacts to the switch. The switch will need to be secured to the body of the flashlight.

Assemble the pieces of PVC , fish both ends of the magnet wire through the 90 degree elbow, drill a hole in one of the PVC end caps so the LED can “poke” through the end cap.

Next solder one end of the magnet wire to one of the leads on the LED and solder the other end of magnet wire to the other end of the LED. solder the switch into the circuit if you are using it.

Place a shock absorber at the 90 degree elbow and the other end cap.

Slide the magnet into the PVC pipe and shake.

The LED should flicker as you shake the pipe. It does not stay lit continuously because the flashlight generates alternating current and the LED is a diode.



Rectifier circuit and storage







Does the LED light when you shake it?

Is the soldering neat, solid and does it use a minimum of solder?

Is the wire neatly and carefully wrapped?

Does the whole project appear to be done with care and attention to detail?



Do you have a schematic drawing of the electric circuit?

Do you have a drawing of the assembly of the flashlight?

Can you explain the difference between ac and dc current?

Can you name and explain the function of each of the circuit's components? magnet wire/coil, led, diode, capacitor, rectifier, switch

Can you explain the reasons why this device works?



Testing and evaluation

How many volts does the generator make when you shake it?

How many volts does the LED require?

If you have a rectifier and storage feature, how many shakes does it take to light the LED for one minute?




Here is a drawing of a design for the flashlight:

Here is a picture of the flashlight, mostly done, but in process:

If you wrap the coil with tape like this, it will keep the wire from getting tangled:

You can pass the wires from the outside to the inside by drilling a small hole in the pvc:

Use a drill press and a vise if you have it, otherwise, you can use a finish nail in a drill to get a small hole.

Drill some holes on the side of the 90 degree elbow to accomodate the switch.

If the fittings are too loose, you can add some tape to the pipe to make a snug fit:

Wrap the wire on the paddle for measurement and storage, then it will be easy to wrap it on the tube as well.

Here is a photo comparing two flashlights, one fully functional with a rectifier and capacitor (not visible), the other was only partially completed in the factory. Both work off the shelf, but only one will charge the battery through shaking.

Out of the lower flashlight, you can see the bumpers and the neodynium 'rare earth' magnet.

This pen is about to become a donor to the shake flashlight project.

Here the magnet is wrapped with electrical tape to keep it running smoothly in the raceway.

The cardboard helps keep your wire wrapping organized and relatively neat.

This system doesn't allow you to measure the wire. A painter's paddle makes a great measuring stick/storage system. The paddle is 2' for a complete rotation and can be stored indefinitely. 75 wraps on the paddle is 150 feet. Put it in the locker with your name on it and you can finish it later

Scrape the insulation from the magnet wire or it will not conduct.

Cut the ink cartridge from the pen and put two little pieces on either end of the raceway to serve as bumpers.

This light works with a pen for a body, 4 3/8 inch ceramic magnets and 32 guage wire. It does not have a rectifier or a storage capacitor.

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