Originally conceived of and deployed by the Graffiti Research Lab, LED Throwies are a cheap, quick way to create glowing orbs of goodness that stick to any ferro-magnetic surface. Since the parts are inexpensive and the concept is easily grasped, this is a great first electronics project or a fun challenge for seasoned makers. There are a ton of variations on the idea, everything from LED Jellies to another LED Floatie (in a balloon) and each is a unique response to the environment it lives in and the function it will perform.
When a group of friends decided to ring in the New Year in LA at our friend's house with a pool, we decided that our contribution should involve water. Hence, LED Floaties were born. Subtract the neodymium magnet, add a ping pong ball, and you have days of glowing circular pixels perfect for light wars or light art. We made 200, which was not nearly enough to fill the pool, but definitely enough for a week's work of LED fun.
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Step 1: Gather Materials
1) 5mm Diffused lens LEDs (I like the ones from Evil Mad Scientist)
A note on which LEDs you should get: For this particular project, I would suggest 5mm with a diffused lens. It has a wide viewing angle that allows the light to permeate the ping pong ball, giving it a soft, haloed appearance instead of a laser inside of a white ball.
2) 3 Volt battery (These are much cheaper bought online)
3) Masking or Electrical Tape
6) Exacto Knife
Step 2: Make Light!
First, look at your LED and identify the long leg, or anode, and the short leg, or cathode.
Next, examine your 3 volt battery and find the side with a ‘+’ on it. This is the positive side of the battery. You will want to connect the long leg of the LED to this side and the short leg to the negative side. If you connect it the right way, the LED should light up. If not, try switching the legs - this won’t hurt the LED since the voltage is so low.
Step 3: Attach the LED to the Battery
Hold the LED on the battery so you are looking at the anode. Position the LED so the top of the battery is at the midpoint of the LED leg.
Now we will want to tape the LED to the battery. Ideally the tape should be light-colored masking tape, duct tape, or electrical tape. Do not use transparent Scotch tape - it does not maintain as strong a connection and you may end up with unlit ping pong balls. Take about three inches of tape and wind it around the LED and battery. Be sure it is secure.
Step 4: Adjust the LED
Now we want to readjust the LED. Holding the battery, bend the LED so its legs make a 90 degree angle. This will make it easier to fit inside the ping pong ball and will allow the LED to move around inside it.
Step 5: Cut Open the Ping Pong Ball
This is an important step: messy slits will cause you massive frustration later!
Next, it’s finally time to open up the ping pong ball using a sharp Exacto knife. Let’s look at the ping pong ball. You should see a seam that goes around the circumference of the ball. Do not cut along or into this seam. Take your Exacto knife and make a small incision. Gentlely run the knife across the plastic in a straight line that has a length of about half the circumference. Remember that you will have to glue this later, so try to keep this cut as thin as possible. And do not cut the ball in half!
If you are making a lot of these and start a production line, you want your neatest, most neurotically meticulous people here.
Step 6: Insert the LED/battery
Placing your fingers at the edges of the cut, apply slight pressure so the slit opens. *Carefully* slide the LED/battery combo into the ping pong ball. This might take a little negotiation between you and the ping pong ball. Be sure not to force it in and make the cut larger in the process.
Step 7: Glue the Ping Pong Ball Closed
Using a low heat glue gun, apply a generous amount of glue across the cut to seal it up and hold for 20 seconds or until dry. Look for any holes and reapply.
Do not use a high heat glue gun - it will double the drying time. You will spend more time holding the ball closed and use more glue to seal up holes.
Step 8: Throw Them in the Water!
Throw them into the pool and let the light wars begin!