The Track-O-Lantern is based upon the Instructable done by DIYHacksAndHowTos. Please vote for them for the Halloween Props contest, without their Instructable, this one wouldn't be here. I used their code and circuit with one exception, I used two servos for the two eyes but they are wired together so the movement is in synch.
The Track-O-Lantern's eyes will follow you as you walk back and forth in front of it. The eyes will follow your movement as you cross in front of the light sensors. The sensors are read by the Arduino and the servo turns according to which resistor is triggered.
2 pieces of 1/2" copper pipe about 3" long
2 end caps for 1/2" copper pipe
2 Brackets (2" x 2")
2 Small Bolts with nuts and washers
Hot Melt Glue
You can get most of the parts at the Home Depot or on ebay.
I found these walking eyeballs at the Dollar Store that are a good size for a pumpkin and THEY GLOW IN THE DARK!.
You might find other eyes out there or just use ping pong balls and paint pupils on them.
I took them apart with a screw driver and took the walking mechanism out and them screwed them back together.
Glue them to the horn of the servo.
I set up the circuit and did a quick test as shown in the video below.
I then made a mount for the eyeballs out of the copper pipe and bracket. Drill a hole in the end cap for the small bolt.
Insert the bracket as shown and tighten then press onto the copper pipe.
Use the zip ties to secure the servo to the bracket, or just use electrical tape.
Carve your pumpkin. I only carved out the surface of the pumpkin for the nose and mouth so that the servo mechanism couldn't be seen.
I drilled out a hole in the bottom center of the pumpkin and inserted a small night light. I then inserted the copper pipe with the servos into the pumpin and adjusted them until they looked lined up in the pumpkin eye sockets.
I ended up putting the pumpkin on a table I had and hid the sensors under some black tape. The wiring came out of the back of the pumpkin and the Arduino is attached underneath the table out of sight. I plugged it in and then tested it.
It takes a bit for the sensors to adjust, so don't be discouraged. Also, make sure that the eyes are foward when the center sensor is activated.