For the LED contest, I wanted to put lights on something that moves. Poi are something I've been tempted to try for a while, and seemed like a good application for LEDs.

Step 1: Materials

These poi are constructed from a pair of hollow rubber balls on ropes. I've inserted 5 LEDs in each ball, powered by 12V batteries. The ball is covered with a balloon.

Things you'll need:

- 2 hollow balls - mine are around 3 inches in diameter
- 10 (or more) LEDs and some spares
- electrical wire
- 2 12V batteries (it's possible you'll need more power if you use more LEDs)
- rope
- 2 balloons - I used 12 inch balloons
- electrical tape
- four large washers (to add some weight to the balls)
- velcro and conductive thread (I used these to make a switch)
- glue

You'll also need a soldering iron, wire strippers, a drill, a utility knife, a needle, and pointed scissors.

Step 2: Test Your Circuit

First, decide how many LEDs you are going to use. It is helpful to use a breadboard or similar to test the LEDs with your intended power source.

I ended up deciding to wire the LEDs in series and not use a resistor, but your circuit may be different if you use more or fewer LEDs than I did.

My poi use standard 5mm green LEDs. (I was originally intending to use super bright LEDs, but I broke one and didn't have a spare.)

The 12V batteries are conveniently small enough to fit inside the balls, and 1 battery provides enough power for the 5 LEDs.

Step 3: Drill the Holes

You'll need one hole to attach the rope, and one hole for each LED.

Decide how you want to arrange the LEDs, and mark all the holes on the ball. Keep in mind that you're going to be cutting the ball in half to wire up the circuit. All the LEDs should be in one half, and the rope should attach to the other half

Then drill the holes using a bit that is very slightly smaller than the diameter of the LED. I did this on a drill press, but any type of drill should work as long as you're careful. A roll of electrical tape works well as a stand for the ball.

Next drill two smaller holes to run electrical wire through. One wire will come from each end of the circuit, so the holes should be near (but not too close to) the larger holes for the LEDs at the start and end of the series. Have a look at the third picture which shows how things are going to look from the inside of the ball.

Step 4: Start the Assembly

First, cut the ball in half. You can do this with a utility knife, and it doesn't matter if the cut is jagged. (It might make it easier to fit the pieces together later.) Make sure you don't cut too close to the holes, though, and remember that the hole for the rope should be in one half and the holes for the LEDs in the other half.

Now you can attach the rope. Tie a knot in one end of the rope, and put a little glue on it so it doesn't come untied. Thread a couple of large washers or similar items onto the rope to give the poi some weight. Then, thread the end of the rope through the rope hole and pull the washers up so they fit inside the half of the ball.

Step 5: Solder the LEDs

Push the LEDs into the holes from the inside of the ball. Keep track of which lead is which (the long one is the positive lead, and the short one is the negative lead). You're going to wire them up in series, meaning that the positive lead from one LED gets wired to the negative lead from the next LED.

My LEDs were close enough together that I just folded the leads down and soldered them together. If yours are further apart, you may need to use a short piece of electrical wire to connect them.

Cut two more pieces of electrical wire and strip the ends. Tape one wire to each end of a 12V battery. Squeeze the ends of the batteries to make sure the wire is making a good connection with the battery.

At this point, you can touch the positive lead from the battery to the un-soldered positive LED lead, and the negative lead from the battery to the un-soldered negative LED lead, and the LEDs should light up. If not, check your circuit for bad connections. (A multi-meter is useful here.)

Assuming your circuit works, you can finish the circuit. Cut another piece of electrical wire and strip the ends. Thread it through the small hole at the negative end of the circuit. Solder the inside end to the negative LED lead.

Then thread the negative battery lead through the other small hold. Solder the positive battery lead to the positive LED lead.

Use some electrical tape to hold the battery in place. At this point, touching the two wires together will light the LEDs.

Step 6: Assemble the Poi and Make the Switch

Fit the two halves ofthe ball together and use some tape to hold them in place. Run the two wire leads up the ball to the rope, and tape them down.

Cut the neck off a balloon and discard it. Stretch the balloon out, and insert the ball. The rope and the wires should come through the opening of the balloon. Using pointed scissors, trim the opening of the balloon so it lies flat against the ball. Then cut tiny holes for each LED. Be careful here - it's easy to make the holes too big. Cut a very tiny hole at the top of the LED and then pull it down so it stretches around the LED.

To make the switch, cut a small piece of velcro (both the loop and hook sides). Using conductive thread, sew back and forth across the loop side of the velcro. Form one of the wire leads into a loop, and stitch the conductive thread through the loop several times to make a good connection. Glue the loop side of the velcro down over the loop of wire. If you position it partially under the balloon, the balloon will help to hold it in place while the glue dries.

To close the switch, put the second wire on top of the conductive thread, then stick the hook side of the velcro on top of it to hold it in place. When the switch is off, you can stuff the wire and the hook side of the velcro under the edge of the balloon so you don't lose them.

Once the glue has set, you can trim the balloon if you need to expose more of the velcro.

Step 7: Tying Up Loose Ends

Now you just need to tie a loop in the rope to use as a handle, and you're ready to learn to spin your poi!

Unless, that is, you only made one. In that case, go back to the beginning and make the second one. =)

Credits:

Thanks to my dad for help working out the power requirements of the LEDs, and for the use of the drill press.

And thanks to Instructables user Kabapu for the excellent long-exposure photographs.