LED Ping Pong Ball Jack-O-Lantern

When it comes to pumpkins, I go for the classic look. A couple of round(ish) eyes, a triangle nose, and a mouth missing a couple of teeth. Voila! This year though, I wanted a little more. Thus the LED Ping Pong Ball Jack-O-Lantern was born. This little guy looks creepy in the daytime with the bulging white eyes and really creepy at night with red glowing orbs of death. Add a flickering candle effect and now we have a pumpkin that will make anyone stop and look.

The bits needed for this project are pretty straightforward.

• Pumpkin
• Pencil
• Knife
• Spoon
• Drill
• 1-1/2 inch drill bit
• 5/32 inch drill bit
• Soldering Iron
• Solder
• Wire
• Three ping pong balls
• Wire cutters and strippers
• Three 5mm red LEDs
• Two 5mm yellow LEDs
• 5 220 ohm resisters
• Micro-Controller, breadboard, and connection cable
• 5v power supply
• Electrical tape

I prefer using a pencil to mark my jack-o-lanterns before I cut them. The reason for this is that I don't usually follow the lines I drew and pencil marks are easy to erase. If I use a pen or a marker, I have to be much more precise in my cutting or I end up with unsightly dark lines that I should have removed.

Whatever method you chose do use, draw the face you want your jack-o-lantern to have. Don't worry too much about making sure that the eyes are perfectly round. We will take care of that when we cut them out.

Also, keep in mind that the inside of your pumpkin will have several wires hanging around. The more of your pumpkin that you remove, the harder the wires will be to hide.

Here is one of the best pumpkin carving tricks ever. Both my son and I hate, and I mean Hate with a capital "huh" to stick our hands in the tiny hole that inevitably gets cut out of the top to scrape the seeds out. If you cut the hole in the top but instead of making it round, cut down the back of the pumpkin also, you have a nice big space to dig the innards out. Easy as pi.

Of course, you could throw all those yummy pumpkin seeds away. On the other hand, how about a nice snack. Put your seeds aside and take a look at one of these fine Instructables on how to make that slimy mess into an excellent treat.

Using your knife, cut the nose and mouth out first. I like to use the nose as a reference point for everything else so I usually start there. If the mouth ends up a little skiwampus, that is ok. The effect of a slightly messed up jack-o-lantern is a little more unnerving than one that just happily grins at you.

For the eyes, here's the trick: Most ping pong balls are 40mm in size.
A 1-1/2 inch hole will barely be big enough to hold the ping pong ball. This allows the ping pong ball to stick out and give your jack-o-lantern the bulging eye look. If you want to sink your ping pong balls deeper into the eye holes, you will need a bigger drill bit. I didn't have a bigger bit so I wanted 1-1/2 inch holes.

When drilling, there are a few things to remember:

DO NOT DRILL TOO FAST

I can not stress this enough. If you push through the pumpkin too fast, you will end up with a very poor hole. You will likely tear the skin of your pumpkin around the hole. Look at the second picture of the eye holes and you will see a piece of skin missing from the 1 o'clock position. This happened for two reasons: I was pushing too fast and the drill was not spinning fast enough. This brings me to tip number 2.

MAKE YOUR DRILL SPIN AS FAST AS IT WILL GO

There is a downside to this. The faster your drill goes, the more you will splatter pumpkin guts everywhere around you. You win some, you lose some.

Once the eyes are done, clean up the back of your holes and you are done carving your pumpkin. Clean up your mess, sit back, and take five. It is time for circuitry.

First off, plug in your soldering iron and let it heat up. While that is going on, get your wires, LEDs, and resistors ready.

You will need 10 wires total. The first four (the red and black wires on the right in the first picture) should be long enough to go from the back of your pumpkin's eyeballs to the bottom of the inside of your pumpkin. The other six wires just need to be long enough to make sure that the ping pong ball that you will use for the "fireball" does not sit on top of the nano and the breadboard. I used red wires for the positive side and black wires for the negative side.

My black wires were too large to fit in the holes of my breadboard so to solve this problem I soldered the resistors to the ends of the black wires. The other ends of the black wires were soldered to the cathode (or negative) sides of the LEDs. The red wires were soldered to the anode (or positive) sides of the LEDs. Do this for all of the red and yellow LEDs. When you are done, you should have five separate LED lights with a black wire and resistor on one side and a red wire on the other.

I had a buddy tell me that if I generated too much heat from drilling holes in the ping pong balls they could catch on fire in my hand. I suppose that it is possible but I didn't experience it. At any rate, not letting your ping pong ball catch on fire might be a good idea so be careful.

Using a drill bit that is just a hair smaller than your LEDs (mine were 5mm so I used a 5/32 inch drill bit), drill a single hole the back of the two ping pong balls that you are going to use of the eyes of your jack-o-lantern.

Notice in the first picture on this page that there is a seam in the ping pong ball. When you light up the ball with an LED, that seam will be very visible. If you don't want that seam showing, you will need to make sure that the seam is hidden in the pumpkin. To do this, when you drill the holes for the LEDs drill the hole in the rear center of the ping pong ball. In other words, imagine that the seam is the equator. Drill the hole on the north or south pole.

Once the holes are drilled, insert one of the red LEDs into the hole in each ping pong ball.

Because ping pong balls are flammable, it would not be a good idea to use a candle in this jack-o-lantern. However, any self-respecting jack-o-lantern would be ashamed to not have a candle so we need to do something that will give your jack-o-lantern some street cred. Thus, the fireball:

On your remaining ping pong ball, drill three holes that are spaced far enough apart that the holes do not touch. Insert your two yellow LEDs and the last red LED into the three holes you just drilled. Cover the exposed connections with tape. This is your fireball and will give the flickering appearance of a candle that your jack-o-lantern so desperately needs.

Before you start connecting the lights to your breadboard, you will want to upload the sketch to your micro-controller. This is the sketch that I used. It is well documented so it should be pretty easy to understand. The values for the three LEDs in your fireball can be adjusted to make your "fire" more red or yellow. You can also change the delay to make the "fire" flicker more or less.

You could also get really creative and make the eyes do fun things as well.

Make whatever changes you want to the sketch then upload it to your micro-controller.

It's time to connect your jack-o-lantern's eyes and fireball to the micro-controller. I used a Chinese knockoff of the Arduino Nano because if it was stolen I would not be too upset. Connect the resistors on the black wires of the fireball LEDs to the negative rail on the breadboard. The red wires coming off of the fireball should be connected as follows:

• connect one yellow LED to pin 3 on the nano
• the other yellow LED to pin 5 on the nano
• the red LED on pin 6 of the nano.

Before you connect the wires for the eyes to the nano, you will need to insert the eyes into the eye holes you drilled in the pumpkin. First feed the wires for the eyeballs into the eye holes from the front. Fit the eyeball in place remembering to pay attention to where the seam ends up. The ping pong ball defuses the light from the LED quite nicely so if the LED is not lined up perfectly with the hole it will be OK. Just make sure that the wires from the LED are clear of the pumpkin and do not short out on each other.

Once the eyeballs are in place, connect the resistors on the black wires of both eyeballs to the negative rail on the breadboard. Connect the red wire from the left eyeball to pin 12 on the nano and the red wire from the right eyeball to pin 10 on the nano.

Below is both a schematic and a layout for your breadboard that you can follow.

That is it. You are done. Find a nice spot for your new creation and power it up. Have a Happy Halloween!