Halloween Skull Window Display

Special thanks to long-time Parallax friend and contributor Carol Hazlett for this spooky Halloween project idea!

This is a display of a laughing skull with a moving jaw for putting on your window sill during Halloween. The skull is simple to make with a 3D printer, but you can also purchase a skull decoration at places like Hobby Lobby, JoAnn’s and Michaels. My first incarnation of this was with a store-bought skull and did not have an articulated jaw.

Some soldering is required for the (#28085) RGB LEDs used in this project. Instructions assume the LED modules are fully assembled and ready to use.

Items needed:

(1) - Parallax Propeller Activity Board WX (#32912) [1].
(1) - Portable Mini Hamburger Speaker (#900-00018) [2]
(1) - ActivityBot Speaker Mount (#725-32905) [3]
(3) - WS2812 RGB LEDs (#28085) [4] Also available as a 10-pack.
(3) - 3-pin extension cables [5], of lengths needed to connect the LEDs for your project.
(1) - Parallax Standard Servo (#900-00005) [6]
Skull - which I downloaded from Thingiverse [7].
Mounting platform for skull. I have a 3D printed one on Thingiverse [8] or you can make one from plastic, wood, or heavy cardboard. If you print it use the design with the cut out for the jaw.
Jaw holder for mounting jaw on servo horn. Again there is a 3D printed version but it is also easy to fabricate in other ways.
Holders for the RGB LEDs which will hold them in place inside the skull [9]. As with the platform they are simple to make out of other materials if you cannot 3D print them.
Various spacers and hardware such as screws and nuts. For the skull I mounted it 40mm above the Propeller ABWX with stacked combo of a 1” and a ½” spacer.
Download any spooky noise wav file you would like. I used a laugh and timed the jaw to match the laugh to give it a little more realism.
- If you have SimpleIDE installed, follow the directions provided in the Play WAV Files tutorial here [10] to load the wav file of your choice to your SD card.
- If you do not have SimpleIDE installed, you will need an SD card/USB adapter you can plug into your computer to load in your wav file. See the tutorial above for filename limits and other restrictions.

Skull Mounting and Coding

One of the first things to do is to cut the jaw from the skull, if possible.

It is fairly easy with the printed skull but may be harder with a purchased skull. If it's not possible, it will still make a nice display, even without a moveable jaw.

The skull's jaw was removed so that it could be attached to the Standard Servo.

Attach the servo to the bottom of platform with screws and nuts trying to get the servo horn as near the center of the platform underside as you can.
- If you use the 3D file there are servo holders built in that already locate the servo in the correct position.

Do not attach the jaw yet.

Skull Display RGB LED wiring.

Wire the RGB LEDs by using servo wires to go from SI side of circuit board to SO side.
Use three LEDs and leave the SO side of last one open.
On the Propeller ABWX breadboard install a 1000uf capacitor in between VCC and GND of servo wire at beginning of LED chain.

RGB LED Schematic for the Skull Display.

The collage picture also illustrates putting an LED into eye holder. I did not glue LEDs into the sockets, so they could be removed if need be.

Place the plastic spacers behind the eye sockets and glue in place.

Install the round spacers with glue behind the eye sockets. CA glue works well on PLA.

If you have wired the LEDs ahead of this step, you should be able to turn them on to locate them precisely. There is quick-start code for the RGB LEDs in the BlocklyProp for Propeller Boards Reference section [11].

The assembled base for the Skull.

Assemble the stand with the servo being under the platform you will be mounting the jaw on. Make sure to have the Propeller Activity Board on the back side of your assembly (facing the platform the skull sits on) to give the jaw room to move.
Then zero your servo using BlocklyProp. Refer to the first image on this page for placement of the jaw lever. Again, there is a lever in the 3D printing files, but you may choose to make your own. I used screws and nuts to attach it to servo horn and CA glue to attach it to jaw.
After jaw is on carefully place skull on top of platform, moving it around until it lines up with jaw.

Skull on Display Platform.

This is how mine ended up looking.

Install the speaker on the side of the platform using the mounting hardware, and plug it into the Propeller ABWX's audio jack.

You should have loaded your SD card with sound already as was mentioned on the list on the front page. Do not forget to turn the speaker on when activating your display!

Side profile of the Skull Display.

This a copy of my Blocklyprop for this project. Please feel free to improve it!

BlocklyProp code for the Skull Window Display Project.

Happy Halloween and I hope you enjoy this project.