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Blink an LED without a battery!

The battery-less L.E.D. blinker

I came up with this little device because I was looking for something that clearly demonstrates the principal that a magnetic field passing through a conductor produces electricity. While a galvanometer will demonstrate the same principal, the L.E.D. blinker seems to really bring the idea home, especially for younger students. Everyone recognizes L.E.D.s as being an indication of electricity.

Construction of the device is simple. All you will need is:

1* 3/8" by 3" carriage bolt. It must be attracted to a magnet. Just about any size bolt will work.
Magnet wire, 24 - 30 gauge is perfect, other gauges will work fine too.
2 * 3/8" fiber washers. Not metal washers. Make sure they fit your bolt.
1 * 3/8" nut, make sure it fits the bolt too.
1 L.E.D., whatever color you like. Not ultra bright types.
1 magnet. Note that NIB magnets are too strong for most students
Electrical tape
Hot glue (epoxy and similar glues will work fine)

Radio Shack sells an assortment pack of magnet wire, part #278-1345B. It has enough wire to make this and all the other electricity and magnetism projects on these pages. They also have the L.E.D. and the magnets. The fiber washers can be a little trickier to find, but a good hardware store should have them. Nylon would work fine too.

All images can be clicked for a larger view.

Start by taking one of the washers, and making a notch and a hole in it as shown. The hole should be at the height that you want the coil to stop. Make sure it is far enough from the edge to be strong. I use a push pin to make the hole, and a small file to make the notch.

Wrap some electrical tape around the bolt, just about an inch.

Now slide the modified fiber washer up to the edge of the electrical tape. The tape should help hold it snugly. Thread the wire through the notch in the washer as shown. Leave a tail of an inch or two, and bend it gently as shown.

Slide the other fiber washer onto the bolt, and sandwich the wire between the two washers. Then thread the nut on and hand tighten it to hold the wire while you wrap.

The number of turns really doesn't matter. I wrap my coils until the wire gets up to the level of the hole in the fiber washer. I make only the most rudimentary efforts to keep the coils neat. Once you are done wrapping, remove the nut and the second fiber washer, and thread the wire through the hole in the first fiber washer. It's a good idea to tape the coil, or at least be very careful during this and the following operations, so that coil doesn't unravel

Snip the wires to an inch. Remove the insulation from the ends of the magnet wire, but make sure to leave 3/8" or so next to the modified washer. I use the edge of a pair of scissors to perform this operation, but be very careful not to cut the wire. Now, bend the leads of the diode like a bowlegged cowboy so they go around the bolt. It is of course essential for there to be no contact between the leads and the bolt. Wrap the stripped end of the wires around the leads of the L.E.D.s. Solder them in place, and snip the excess off. Line the L.E.D. up so that it is right at the edge of the washer.

Check again that the leads are away from the bolts. Squirt some hot glue onto the washer and diode leads, then quickly put the other washer on. Hold it all tight until the glue starts to harden, then remove any excess before it hardens completely. You can always warm it up to soften it again. Now thread the nut on snugly. I use a drop of low strength thread locker to make sure the nut stays in place without having to tighten it too much.

Take the magnet, and wrap a few layers of tape around it. You are now ready to blink! There are (at least) two ways to make the L.E.D. blink. You can pass the magnet quickly past the head of the bolt as shown below.

Using this method, the L.E.D. will blink when you pass the magnet by in either direction, regardless of which side of the magnet faces the L.E.D., and produces a nice bright flash easily seen indoors.

The second method is to bring the magnet in contact with the head of the bolt along the axis of the bolt, i.e. bring the bolt head and the magnet together quickly, but not hard enough to break the magnet. You will find that this method demonstrates that diodes only allow electricity to flow in one direction, as the blinker will only light up in this fashion using one side of the magnets. Using the other side does not produce a blink.

Many variations in material and methods will work. I coat the wire wraps with a liquid electrical tape product to protect the wires. If you will be using the blinker with students I recommend do this or something similar. You could also wrap the wires with tape. I like the liquid rubber stuff because you can still see that it is a bunch of wire wrapped on a bolt, and the point of this device is to make the process as plain and visible as possible. I plan to try some see-through product at some point.

Originally the bolt and L.E.D. were separate, with the L.E.D. being mounted on a small piece of wood. This allowed the bolt to be used as both an electromagnet and a generator. The draw back was that students often hooked up a battery to the L.E.D., And poof, another blown L.E.D.. The model shown above has withstood many students and they all still work.

Why does it work?

The magnet is surrounded by an invisible magnetic field. Whenever a magnetic field passes through a conductor, an electrical charge is generated. So, as the magnetic field passes through the wires wrapped around the bolt, it makes a current flow, and the L.E.D. blinks. For more information about this process, click HERE.