Halloween is quickly approaching, and it's, of course, my favorite DIY time of year. I wanted to introduce my visitors to the holiday festivities and what better way than a creepy skull!

Adafruit has created "The world's most esoteric Pi accessory"! So yes, I'll order one of these "Animated Snake Eyes Bonnet for Raspberry Pi". I am really excited to see what other people will do with these things, but I found a plastic skull that seemed to be a great fit!

Here's what I did...

Step 1: Bill of Materials

Here's what you'll need.

Plastic Skull (or Pumpkin)
Raspberry Pi 3 Model B or 3 B+ (I used a 2 with no problem)
Adafruit Animated Eyes Bonnet for Raspberry Pi
2 - Adafruit TFT 1.54" Screens (I bought the kit and these came with it along with the wiring)
3D Printed Eye Holder (Custom Designed and printed, files in description)
2 - 1.5" Acrylic Cabachons (These were difficult to find otherwise)
Silicon Sealant or equivalent (Home Depot)
Lithium Battery or USB Cable (Amazon or other)

Step 2: A Trip to the Craft Store

So I found an expensive plastic skull at a big box craft store and I used the coupon on my phone to acquire it inexpensively. I carefully carved out the eyes and cut out the base. My criteria was a skull that was mildly realistic, easy to cut/carve and sufficient size to hold some 1.5 screens, Raspberry Pi with the Shield and maybe a battery.

Step 3: 3D Printing

This was a tricky part and I ended up making a number of prototypes in Fusion 360. Getting the fit right for the acrylic cabochons was an iterative process. Eventually, I settled on a design that had the wires come out the back and from the top.

I printed it in black PLA and screwed the parts together gently. The LCDs are fragile so care needs to be taken. The cabochons I settled on were a bit more expensive than finding them on Amazon and I highly recommend the ones from Tap Plastics. The extra depth is important for the 3d view. I was unimpressed with the ones I originally bought on Amazon.

The STL files are included. I'll post them on Thingiverse as well.

Step 4: Electronics

Adafruit is an outstanding resource for those of us who are not electrical engineers. They have an excellent resource for their Animated Snake Eyes Bonnet for the Raspberry Pi. With a few soldering skills, the shield is very easy to put together. The wiring is straightforward but just double check your work and the orientation. The wires come from the top of the LCDs at least with the TFT displays. They have a 3D carrier to print for their boards and some acrylic cabochons if you can get them. It's awesome when they first power up.

Step 5: Programming/Software Installation

Before you get fancy and start modifying code, etc., follow Adafruit's Software Installation Procedure. You'll need some familiarity with Raspberry Pi's and their setup. Not tricky but pay attention to the details especially to what screens you have and how they are installed.

When you get it all working, pat yourself on the back.

Now you can make it your own.

I played around with this project for a few weeks and eventually settled on a design and behavior. I liked the eyelids and the blinking effect, but I wanted the skull with no blinking. The eyes seem to float in the sockets creepily. If you're a dead skull you don't have any eyelids anyways, right? To remove the eyelids, adjust the code in /boot/Pi_Eyes/eyes.py lines 567-570 labeled right and left upperEyelid.draw() lowerEyelid.draw() can just be commented out with a # sign before each line.

I changed the eye itself with the dragon eye, etc., but the non-realism just seemed cartoonish so I left the default eye in place.

Step 6: Installing the Eyes

I put a lot of thought into this step. You need an adhesive that will bind to the plastics and give it some bulk. I thought my choices were museum putty, silicon sealant, and spray foam. My museum putty couldn't be found but that would only be a temporary fix. The spray foam would be messy and I wasn't sure it would stick. I settled on silicon sealant with a long nozzle to get down in there. I also put a little sealant on the wires so they wouldn't come off. I let it set for 24 hours with ventilation.

Step 7: Finishing Touches

After the eyes are installed, and the sealant is dry, you can put the computer inside. I had some concerns about the heat the RPi 2 would generate, but even after a few days of running nonstop, the skull was barely warm. I wonder if RPi 3 would cause more heat issues, but I doubt it. The RPi 3 can be a little more sensitive to current delivered so often a beefier and shorter micro USB cable is necessary. I had no trouble running the skull off a six foot USB cable and a lithium battery. If I am going to use this for a costume accessory, I'd definitely use a Lithium USB battery. I have an Anker 1300mAh battery that will run the skull for >5h. Plenty of time for a Halloween party.

Step 8: Displaying the Creepy Cranium

So whether you bring Creepy Cranium to the party or sit her on a shelf, you're sure to please the guests. The eyes are really quite bright. Which makes it difficult to photograph because your eyes do such a better job of equalizing the contrast. The extra brightness gives it an unworldly effect in person. It really looks like two globes suspended in space complete with blood shot sclera. The detail is exquisite. I am very pleased with the effect.

Best of luck making your own Creepy Cranium. It's totally worth it.