This is a really simple project. It only takes 5 parts, about 10 minutes and costs around $2. BUT it's fun and looks really cool.

I like LEDs (who doesn't?) and have acquired all different kinds to use in projects, we are going to use one you may not have used yet - a flashing RGB LED.

"Regular" RGB LEDs have 4 legs as opposed to single color LEDs that have 2 legs. Being able to control all 3 colors independently is cool but you do need 4 wires, 3 resistors and some type of controller.
There is a much simpler version out there - flashing RGB LEDs. These LEDs only have 2 LEGS ( + and -). So how do you control the colors? You don't. There is a teeny tiny chip wired up to the LEDs inside their plastic housing that turns each LED on in varying degrees creating a color changing flashing pattern. They come in 2 flavors, fast flash and slow flash.

One characteristic of LEDs is they are usually pretty directional. What I mean by that is when you look at them from the side you see one level of brightness and color and if you look at them head on it's completely different. They sell diffused LEDs that have a frosted epoxy case/lense/housing but a ping pong ball works even better for defusing the light!

Some of the most fun I have had with these is when I put them in unusual places at night like in the grass of my front yard or bushes or under my car. People have all kinds of reactions. Of course sometimes I just turn it on at my desk and stare into the abyss.

Step 1: Stuff Needed

Parts

Ping Pong Ball - I got mine from the Dollar Store 6 for $1
Coin Cell Battery Holder - eBay
Coin Cell Battery - you have a number of choices, the most important thing is that it fits your battery holder, CR2032 and CR2025 are the most popular, I used a rechargeable version of the CR2032
A Resistor - The value you use will be dependent on the battery and LED you choose, more on that later
Flashing RGB LED - Slow or Fast they work the same as far as this project goes

Tools

soldering iron
glue gun
hobby knife
compass (optional)

Notes and Links

The battery holders I used have 2 pins that stick out the back, here are some examples, you can get 10 from China for about $1 http://www.ebay.com/sch/i.html?_from=R40&_trksid=p...

The batteries themselves are very easy to come by, you can get 10 regular CR2032s (3V) from China for less that $2 http://www.ebay.com/sch/i.html?_from=R40&_trksid=p...
If you want the rechargeable coin cells look for LIR2032 (3.6V) I got 20 for around $10 make sure they say LIR and 3.6V http://www.ebay.com/sch/i.html?_odkw=cr2032+10pcs...
For the flashing LEDs make sure they are RGB LEDs not regular red or blue flashing LEDs You can get regular or diffused the regular ones will be a little brighter in the ping pong ball. Also decide on fast of slow flashing, personally, I like the effect of the slow flashing (it's more like morphing) LEDs http://www.ebay.com/sch/i.html?_odkw=lir2032&_osa...
Picking a resistor value can be a little confusing, the red LED wants one value, the blue wants a different value and of course most of the time more than one LED is being driven at a time so that would lead to yet more values. What to do? We pick an average and we understand what happens if we go to high or low. If the resistor value is too high, the blue LED will be faint or not on at all but the LED will last a loooooooong time. If the value is too low the red LED will be over driven, it will be too bright or orange/white and it will burn out. At 8 cents a LED and less than that for a resistor you can afford to experiment. With a 3V coin cell and flashing RGB LED start with something around 47-80 ohms. Get yourself a little resistor assortment of about 600 pieces and 30 differnt values for less than $3 http://www.ebay.com/sch/i.html?_from=R40&_trksid=...

Step 2: Cut a Hole in Your Ping Pong Ball

We want the ping pong ball to

fit over the LED
enclose the 2 pins
sit on the back of the battery holder without sliding over the side

Measure the distance between the 2 pins and cut your hole that size (actually a little bigger so it covers the 2 pins

I used a compass to gauge the distance then used it to draw the line I needed to cut with my knife

Cut out your hole and make sure it fits on your battery holder, if it's too small you can cut away a little more, if it's a little too big you can use hot glue to fill in the gap

Tip: if you hold the ball up to the light you can see the seam where the two halves are joined, it's easier to cut the ball if you don't have to cut through the seam

Step 3: Connect Your LED, Resistor and Battery Holder

Solder your resistor to your LED

Your LED will have one leg longer than the other, the longer leg will be the + leg

We will solder the resistor to the + leg of the LED

Wrap one leg of the resistor (it doesn't matter which leg) around the + leg of the LED this will make it easier to solder the resistor to the LED

Solder the pieces together then clip off the excess (top) of the resistor leg and (bottom) of the LED leg, when done it should look like the picture

Solder your LED/resistor to the battery holder

Your battery holder has a + and - pin (see picture) it's important to get the polarity right between the LED and battery holder - to - and + to +

Find the - pin of the battery holder and put a little bit of solder on it (tinning it), you can also tin the + pin as well

Put a little solder on the - leg (the one without the resistor) of your LED

Hold the - leg of the LED against the - pin of the battery holder and solder them together

Now take the + leg of the LED which is actually the resistor leg and bend it so it comes up right against the + pin of the battery holder, solder the two together

You might have to gently bend the legs so the LED is towards the middle of the battery holder making it easy to fit the LED inside the ping pong ball

Test before you move on, put the battery in the holder and make sure your connections are working properly and the LED starts to flash

Step 4: Finish Up

So your LED hasn't burned out and you can see blue in your colors and your LED will fit inside your ping pong ball. The future is ours!

Just put a bead of hot glue around the edge of your ping pong ball and glue it against the back of the battery holder

Congratulations you just made a flashing glowball!

Tip: when I sit my glowball on a flat surface the positive side of the battery holder is a little higher than the negative side so I add a little bead of hot glue on the negative rim of the battery holder to even it up. This makes the base a little more stable and less slippery

I think this is a great project to get started with electronics and maker projects, it's very easy and inexpensive with a pretty good payoff in the end. Please don't burn yourself with the soldering iron or poke yourself with the exacto knife, if you can do that, success is pretty much guaranteed