Introduction: Lighted Newton's Cradle

About: Professional work in various electrical and mechanical fields, obscure sense of humour and typically willing to help... Currently under contract designing environmental monitoring equipment.

OK I'll admit this one is a tricky build. It is all in the alignment and requires quite a bit of patience to get it right. Yes mine is not perfect... Yet!!!

Needs more work on the alignment of the balls!

Step 1: Materials

You will need 5 glass marbles about 1 inch in diameter.
1/8 inch brass welding rod.
Pine slats.
fine wire
5 LEDs
A couple of batteries.

You may also want to reference my knife switch instructable. A simple slider will ruin the effect!

Other materials will be presented as the build unfolds...

Step 2: Prepare the Marbles

You will need to remove the rounded tip of the LEDs in order to fasten them to the marbles. I used an abrasive cut off tool on a Dremel for this. The resulting surface was hazy and not optically pure. This was not of concern as I will explain in a moment.

The marbles will also need a small patch of roughed up area for contact. Again I used the Dremel and an abrasive wheel to grind a small flat on the surface.

The flat of the LED is glued to the ground spot on the marble using Cyano type super glue. This glue has the added benefit of filling all of the grind marks and making an optically pure connection. The last pic clearly shows the LED on the other side of the marble.

Step 3: Make the Base

The base is an open sided box made from glued pine slats. The slats are finished on one side then glued together the outside is then finished as desired. There are holes drilled to accommodate the control and supports. The box build details are in my knife switch instructable.

I decided to use a knife switch on top as well as a support rod set up that was 7 inches long on the top. The support rod holes are 1/8 inch for the brass welding rod and the 3 holes for the knife switch are 3/16.

If you follow my knife switch instructable you will see exactly how the switch works. A small wooden handle was made for the knife switch then the knife switch is assembled to the base.

The upright supports are fashioned from 1/8 inch brass welding rod bent into the proper shape.

The brass rod is pressed onto the holes in the base then a wire is attached to each using a soldering gun and standard solder. This makes the rods into a bus-bar.

The rods are then aligned using blocks of wood to ensure their uniform height. Once they are positioned correctly they are glued into place using super glue and left to dry.

Step 4: Prepare the Balls

The leads of the LEDs must be bent into small uniform circles for proper connection.These are soldered closed then the ends are trimmed off.

The wires used are single strand copper wire that was separated from multi-strand wire. This may not be the best choice but you need a light flexible wire.A single strand of wire is fed through the loops on the LEDs and then soldered in place the strand is then separated between the loops thus eliminating any short circuit.

Begin by marking the exact center of the hanging brass rails and hang one ball. The ends of the hanging wire are fastened with a half hitch. Test for center by placing a straight edge on the base and looking down from the top, gently swing the ball to make sure that it swings parallel to the brass rods.

Once you are satisfied with the ball position solder the ends of the hanging wire to the brass rods. You will need a lot of heat and make sure that this is not a cold solder joint.

Note the position of the anode on the LED as referenced by the flat. Take care to align all the LEDs the same way as you move forward with the build.

The next ball is aligned to the first so that it is just touching but not leaning on the first. This can be a painstaking process but it is absolutely necessary that all the balls are perfectly aligned. Solder this ball in place.

The third follows on the opposite side of the second and is aligned the soldered.

Alternate on the opposite side for the forth and fifth balls.

As I said this alignment is the most fiddly. Adjustments can be made by heating the solder connection at the brass bar and moving the half hitch of wire along the rod using a hobby knife.

The better the alignment the better the energy transfer. The balls will move longer and more uniform when the alignment is perfect.

Step 5: Wiring

If you have been following carefully you will notice my  wiring error...

The wiring is fairly simple. All of the LEDs are connected in parallel with the same polarity to the brass bars. These act as positive and negative leads. The switch is soldered in series with these and an appropriate resistor is chosen to determine the brightness of the LEDs.

The power comes from 2 AA batteries that no longer power my camera. There is still quite a bit of power in these. They are connected in series and taped together to form a 3V cell. This is held to the underside of the wood base by Velcro. Now when the switch is thrown the LEDs illuminate creating the effect.

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