Illuminated "Eyes That Follow" Optical Illusion

This classic "Eyes That Follow" optical illusion creates the effect that eyes are watching your every move.

This easy tutorial can be quickly assembled in 45 minutes. This is also easily adaptable. For example, add a set of "following eyes" to a pumpkin to create a creepy jack-o-lantern, or use a glow stick as a quick-to-setup light source.

Step 1: Materials

Materials
Pingpong ball (1 or 2)
Cardboard Box
Pencil
X-Acto knife or Scissors
Cutting Board
Hole Puncher
Single-Sided Tape
Double-Sided Tape
NeoPixel Strip (length of 10 LEDs)
Adafruit Gemma
3 x AAA Battery Pack
AAA x 3
Alligator Clip Test Leads x 3
Computer
USB Cable - A / MiniB
Black Sharpie Marker
Multimeter for Debugging Gemma and LED strip (in case you need to debug the electronics)

Step 2: Splitting the Pingpong Ball

Use an X-Acto knife (the preferred eye surgery utensil of Terminators everywhere) to carefully cut the pingpong ball in half along the circumference. If a seam exists on the ball, cut along this.

If you do not have an X-Acto knife or similar tool, you can use scissors. In my personal experience, I require two pingpong balls doing it this way. First, carefully poke a hole with the tip of the scissors, then start cutting finding your way to the seam. Continue cutting along the seam. Repeat with the second pingpong ball.

Step 3: Cutting Out the Eyes

Unflatten the box.

Place the two pingpong ball halves on the back side of the box and trace them with a pencil, creating two circles. 

In one of the circles, trace out the contours of your eye. Be sure to leave padding between your eye shape and the circle outline. Use your artistic ability to create something either menacing or a bit on the goofy.

Use the X-Acto knife to carefully cutout the outline of your drawn eye shape.

Flip the the cutout horizontally and place it in the other circle. Trace with your pencil. Cut again using the X-Acto knife.

Step 4: Finishing the Eyes

To create the pupils, use a hole punch to extract two dots from one of the eye cutouts.

Place a small square of double-sided tape on the inside of a pingpong half in the center.

Place the pupil right in the center, using tweezers if you have them, black side up. Push down slightly to ensure good contact with the adhesive. Repeat for the other half.

Tip. Make sure your hands are clean, otherwise you may leave smudge marks on the tape or the pingpong half dome.

Place the pingpong half over the circle outlines and secure with clear tape. 

Reassemble the box.

Step 5: Backlighting

There are two ways about going about doing the backlighting: The Easy Way and The Slightly More Involved but Better Looking Way.

The Easy Way

Put some glow sticks in the box. Close the box. Done.

The Slightly More Involved but Better Looking Way

The following steps assumes you have some knowledge of using Arduino-like products. This backlighting rig consists of an Adafruit Gemma, alligator clips, a NeoPixel strip of 10, and a AAA battery pack with batteries. Start by connect the Gemma to the NeoPixel strip using this configuration:

Gemma D0 to NeoPixel DIN (blue wire)
Gemma 3Vo to NeoPixel +5v (red wire)
Gemma GND to NeoPixel GND (black wire)

Plug the Gemma into your computer with a USB cable, boot the Arduino IDE, and upload the code to the Gemma. The code used to drive the Gemma and NeoPixels can be downloaded here. By default, it makes all the LEDs on the strip red. However, you can change the RGB values in line 10 of the program.

setAll(strip.Color(255, 0, 0));

Once the LEDs are lit up, disconnect the USB cable from the Gemma and connect the battery pack. The battery pack will provide many, many hours of light, enough to last you one Halloween evening.

Place the LEDs in the box. If needed, use tape to secure the LED strip and battery pack.

Tip. The Gemma can be swapped out for virtually any model of Arduino. I recommend doing this as the Gemma requires additional setup to get working with the Arduino IDE. On the other hand, the Gemma only costs $8, so go with this if you know what you're doing.

Step 6: Finishing Touches

Use a black wide-tip Sharpie to darken the label. You can try pulling the label and packaging tape off, but this can lead to tearing off the top layer of the box.

All that's left is to place your spooky box somewhere to catch the eyes of passers-by. Place in a bush, in a tree, on a bookshelf, out a window, etc. I prefer placing it higher up to give the sense that it's looking down on you, watching your every move.

Happy Halloween!