Who doesn't love a good skeleton prop for Halloween? This Instructable shows how to put together a pair of glowing red eyes for your skeleton (or just a skull) which dim and brighten, providing a creepy effect for your Trick or Treaters and other visitors.

Supplies

Begin with a skeleton from Walmart, Target, or one of the pop-up Spirit Halloween stores. The remainder of the supplies are listed within the Instructable.

Step 1: Introduction

After scouring Instructables and the Internet for an off-the-shelf circuit design for dimming LED circuits, I realized I would have to design my own. My circuit is assembled from scrounged parts that I already had, so my cost was zero. Experienced circuit builders will be able to put this together in an hour. Your mileage may vary. Add another hour or two for modifying the skeleton, depending on drying time for the paint.

Knowledge

If you are comfortable with circuit assembly, skip ahead to the schematic and start your project. If you don't know the difference between resistance and capacitance, call your nerd friend and show them this project. They will love you for it.

This project uses sharp objects like knives and saws as well as hot things like glue guns and soldering irons. Please supervise any young folks who build this project or assist you with yours.

Step 2: Materials

Five foot skeleton (from any Halloween store) - $20 to $30

Prototyping breadboard (from electronic supply or Amazon) - $3

9 volt power supply (from music store or Amazon) - $10 to $20 and mating socket - $2

Capacitors: 22uF, .01uF, 68uF (from electronic supply or Amazon)

1/4 Watt Resistors: 47K, 10K (3), 100K, 22K, 1K (2) (from electronic supply or Amazon)

LEDs (2) (from electronic supply or Amazon)

PNP Transistor, general purpose (from electronic supply or Amazon)

555 Timer or equivalent (from electronic supply or Amazon)

Heat shrink tubing (from Home Depot or Amazon) - $5

Reusable breadboard (optional)

Black Acrylic Paint (Walmart or any Hobby Supply) - $4

1 Ping pong ball or equivalent (I used a $2 package of Halloween eyes from Walmart)

Step 3: Tools

Utility Knife

Xacto Knife (optional)

Coping saw

Keyhole saw

Drill and drill bits

Awl

Masking tape or painters tape

Phillips head screw driver

Hot glue gun and glue stick

Wire stripper

Soldering iron and solder

Insulated wire, various colors, 22 to 26AWG

Step 4: Cut Ping Pong Ball in Half and Drill Hole

1. Using a coping saw or your favorite method of inflicting bodily harm, cut a ping pong ball in half.

2. Select a drill bit that will allow your LEDs to fit snugly. Use that bit to drill a hole in the center of both ping pong ball halves.

Step 5: Cut Eye Sockets in Skull

The skull was attached to the skeleton using two small screws. Remove these and detach the skull from the body. Pull the cord out of the skull.

Use a keyhole saw or utility knife to carve out the eye sockets in the skull.

Step 6: Cut Access Door in Back of Skull

The plastic skull is very thin. Use a utility knife or Xacto knife to cut a door large enough to fit your hand through.

Step 7: Glue Ping Pong Balls Into Eye Sockets

Use your hot glue gun to attach the ping pong ball halves into the eye socket holes cut in the previous step. There will be gaps that need to be filled in the next step, so don't worry.

Step 8: Fill in Eye Socket Gaps

Working from inside the skull, use painters tape or masking tape to wrap around ping pong ball halves.

Take the glue gun and glue over the tape from outside the skull to completely fill in any existing gaps where you see tape.

Step 9: Paint Eye Sockets

Use the black acrylic paint to completely paint in the eye sockets. They may require a touch up later on after inserting the LEDs.

This is a good time to add any other paint details to the skull. I darkened the gaps between the teeth so they would stand out.

Step 10: Start Assembling the Circuit

Use the schematic to assemble the circuit. Between errors, testing, and assembly, you will have to solder and unsolder connecting wires more than once. Since I was in a hurry, I made at least five wiring blunders, but luckily, the circuit components are very forgiving. Since the circuit is so small, I was able to cut off the unused portion of the perfboard.

Step 11: Assemble the LED Jumpers

You will need some longer wires to connect the circuit to the LEDs unless you plan on embedding the entire thing within the skull. I attached the 1K resistors directly to the LED anodes (marked + in the diagram). Over all LED connections, I placed heat shrink so there could be no short circuits.

After assembling the jumpers, attach them temporarily to your circuit from the previous step in order to test and ensure that they work. Reach inside the skull and press the working LEDs into the holes you drilled in the ping pong ball halves.

Step 12: It Is Alive!

Now we move to the fun part! Plug everything in and bask in the glow of those lovely red eyes. If you don't need an entire skeleton, you can be finished now and laugh at everyone else.

Step 13: Holes for Passing Wiring

Drill a small hole behind the spinal column to pass the LED jumpers though. Feed the jumper wiring through the hole and pull out any slack. Don't forget these wires will need to be soldered into the circuit board.

Step 14: Pull Hanging Cord Through Skull

I used a coat hanger wire to pull the hanging cord (removed previously) back through the top of the skull. Push the hanger through the hole on top of the skull through the spinal cord hole. Tape the cord to the hanger and carefully pull back out through the top. Detach the hanger.